[alg.modifying.operations]

# 26 Algorithms library [[algorithms]](./#algorithms)

## 26.7 Mutating sequence operations [alg.modifying.operations]

### [26.7.1](#alg.copy) Copy [[alg.copy]](alg.copy)

[🔗](#lib:copy)

`template<class InputIterator, class OutputIterator>
  constexpr OutputIterator copy(InputIterator first, InputIterator last,
                                OutputIterator result);

template<[input_iterator](iterator.concept.input#concept:input_iterator "24.3.4.9 Concept input_­iterator [iterator.concept.input]") I, [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7 Concept sentinel_­for [iterator.concept.sentinel]")<I> S, [weakly_incrementable](iterator.concept.winc#concept:weakly_incrementable "24.3.4.4 Concept weakly_­incrementable [iterator.concept.winc]") O>
  requires [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3 Concept indirectly_­copyable [alg.req.ind.copy]")<I, O>
  constexpr ranges::copy_result<I, O> ranges::copy(I first, S last, O result);
template<[input_range](range.refinements#concept:input_range "25.4.6 Other range refinements [range.refinements]") R, [weakly_incrementable](iterator.concept.winc#concept:weakly_incrementable "24.3.4.4 Concept weakly_­incrementable [iterator.concept.winc]") O>
  requires [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3 Concept indirectly_­copyable [alg.req.ind.copy]")<iterator_t<R>, O>
  constexpr ranges::copy_result<borrowed_iterator_t<R>, O> ranges::copy(R&& r, O result);
`

[1](#alg.copy-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6361)

Let N be last - first[.](#alg.copy-1.sentence-1)

[2](#alg.copy-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6364)

*Preconditions*: result is not in the range [first, last)[.](#alg.copy-2.sentence-1)

[3](#alg.copy-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6368)

*Effects*: Copies elements in the range [first, last)
into the range [result, result + N)
starting from first and proceeding to last[.](#alg.copy-3.sentence-1)

For each non-negative integer n<N,
performs *(result + n) = *(first + n)[.](#alg.copy-3.sentence-2)

[4](#alg.copy-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6376)

*Returns*: 

- [(4.1)](#alg.copy-4.1)

  result + N for the overload in namespace std[.](#alg.copy-4.1.sentence-1)

- [(4.2)](#alg.copy-4.2)

  {last, result + N} for the overloads in namespace ranges[.](#alg.copy-4.2.sentence-1)

[5](#alg.copy-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6385)

*Complexity*: Exactly N assignments[.](#alg.copy-5.sentence-1)

[🔗](#lib:copy_)

`template<class ExecutionPolicy, class ForwardIterator1, class ForwardIterator2>
  ForwardIterator2 copy(ExecutionPolicy&& exec,
                        ForwardIterator1 first, ForwardIterator1 last,
                        ForwardIterator2 result);

template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]") I, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<I> S,
         [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]") O, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<O> OutS>
  requires [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3 Concept indirectly_­copyable [alg.req.ind.copy]")<I, O>
  ranges::copy_result<I, O>
    ranges::copy(Ep&& exec, I first, S last, O result, OutS result_last);
template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6 Other range refinements [range.refinements]") R, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6 Other range refinements [range.refinements]") OutR>
  requires [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3 Concept indirectly_­copyable [alg.req.ind.copy]")<iterator_t<R>, iterator_t<OutR>>
  ranges::copy_result<borrowed_iterator_t<R>, borrowed_iterator_t<OutR>>
    ranges::copy(Ep&& exec, R&& r, OutR&& result_r);
`

[6](#alg.copy-6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6409)

Let result_last be result + (last - first) for the overload in namespace std[.](#alg.copy-6.sentence-1)

[7](#alg.copy-7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6413)

Let N be min(last - first, result_last - result)[.](#alg.copy-7.sentence-1)

[8](#alg.copy-8)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6416)

*Preconditions*: The ranges [first, last) and [result, result + N)
do not overlap[.](#alg.copy-8.sentence-1)

[9](#alg.copy-9)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6421)

*Effects*: Copies elements in the range [first, first + N)
into the range [result, result + N)[.](#alg.copy-9.sentence-1)

For each non-negative integer n<N,
performs *(result + n) = *(first + n)[.](#alg.copy-9.sentence-2)

[10](#alg.copy-10)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6428)

*Returns*: 

- [(10.1)](#alg.copy-10.1)

  result + N for the overload in namespace std[.](#alg.copy-10.1.sentence-1)

- [(10.2)](#alg.copy-10.2)

  {first + N, result + N} for the overloads in namespace ranges[.](#alg.copy-10.2.sentence-1)

[11](#alg.copy-11)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6437)

*Complexity*: Exactly N assignments[.](#alg.copy-11.sentence-1)

[🔗](#lib:copy_n)

`template<class InputIterator, class Size, class OutputIterator>
  constexpr OutputIterator copy_n(InputIterator first, Size n,
                                  OutputIterator result);
template<class ExecutionPolicy, class ForwardIterator1, class Size, class ForwardIterator2>
  ForwardIterator2 copy_n(ExecutionPolicy&& exec,
                          ForwardIterator1 first, Size n,
                          ForwardIterator2 result);

template<[input_iterator](iterator.concept.input#concept:input_iterator "24.3.4.9 Concept input_­iterator [iterator.concept.input]") I, [weakly_incrementable](iterator.concept.winc#concept:weakly_incrementable "24.3.4.4 Concept weakly_­incrementable [iterator.concept.winc]") O>
  requires [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3 Concept indirectly_­copyable [alg.req.ind.copy]")<I, O>
  constexpr ranges::copy_n_result<I, O>
    ranges::copy_n(I first, iter_difference_t<I> n, O result);

template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]") I, [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]") O,
         [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<O> OutS>
  requires [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3 Concept indirectly_­copyable [alg.req.ind.copy]")<I, O>
  ranges::copy_n_result<I, O>
    ranges::copy_n(Ep&& exec, I first, iter_difference_t<I> n, O result, OutS result_last);
`

[12](#alg.copy-12)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6465)

Let M be max(0, n)[.](#alg.copy-12.sentence-1)

[13](#alg.copy-13)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6468)

Let result_last be result + M for the overloads with no parameter result_last[.](#alg.copy-13.sentence-1)

[14](#alg.copy-14)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6472)

Let N be min(result_last - result,M)[.](#alg.copy-14.sentence-1)

[15](#alg.copy-15)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6475)

*Mandates*: The type Size is convertible
to an integral type ([[conv.integral]](conv.integral "7.3.9 Integral conversions"), [[class.conv]](class.conv "11.4.8 Conversions"))[.](#alg.copy-15.sentence-1)

[16](#alg.copy-16)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6480)

*Effects*: For each non-negative integer i<N,
performs *(result + i) = *(first + i)[.](#alg.copy-16.sentence-1)

[17](#alg.copy-17)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6485)

*Returns*: 

- [(17.1)](#alg.copy-17.1)

  result + N for the overloads in namespace std[.](#alg.copy-17.1.sentence-1)

- [(17.2)](#alg.copy-17.2)

  {first + N, result + N} for the overload in namespace ranges[.](#alg.copy-17.2.sentence-1)

[18](#alg.copy-18)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6496)

*Complexity*: Exactly N assignments[.](#alg.copy-18.sentence-1)

[🔗](#lib:copy_if)

`template<class InputIterator, class OutputIterator, class Predicate>
  constexpr OutputIterator copy_if(InputIterator first, InputIterator last,
                                   OutputIterator result, Predicate pred);
template<class ExecutionPolicy, class ForwardIterator1, class ForwardIterator2,
         class Predicate>
  ForwardIterator2 copy_if(ExecutionPolicy&& exec,
                           ForwardIterator1 first, ForwardIterator1 last,
                           ForwardIterator2 result, Predicate pred);

template<[input_iterator](iterator.concept.input#concept:input_iterator "24.3.4.9 Concept input_­iterator [iterator.concept.input]") I, [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7 Concept sentinel_­for [iterator.concept.sentinel]")<I> S, [weakly_incrementable](iterator.concept.winc#concept:weakly_incrementable "24.3.4.4 Concept weakly_­incrementable [iterator.concept.winc]") O, class Proj = identity,
         [indirect_unary_predicate](indirectcallable.indirectinvocable#concept:indirect_unary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<projected<I, Proj>> Pred>
  requires [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3 Concept indirectly_­copyable [alg.req.ind.copy]")<I, O>
  constexpr ranges::copy_if_result<I, O>
    ranges::copy_if(I first, S last, O result, Pred pred, Proj proj = {});
template<[input_range](range.refinements#concept:input_range "25.4.6 Other range refinements [range.refinements]") R, [weakly_incrementable](iterator.concept.winc#concept:weakly_incrementable "24.3.4.4 Concept weakly_­incrementable [iterator.concept.winc]") O, class Proj = identity,
         [indirect_unary_predicate](indirectcallable.indirectinvocable#concept:indirect_unary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<projected<iterator_t<R>, Proj>> Pred>
  requires [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3 Concept indirectly_­copyable [alg.req.ind.copy]")<iterator_t<R>, O>
  constexpr ranges::copy_if_result<borrowed_iterator_t<R>, O>
    ranges::copy_if(R&& r, O result, Pred pred, Proj proj = {});

template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]") I, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<I> S,
          [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]") O, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<O> OutS,
          class Proj = identity, [indirect_unary_predicate](indirectcallable.indirectinvocable#concept:indirect_unary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<projected<I, Proj>> Pred>
  requires [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3 Concept indirectly_­copyable [alg.req.ind.copy]")<I, O>
  ranges::copy_if_result<I, O>
    ranges::copy_if(Ep&& exec, I first, S last, O result, OutS result_last,
                    Pred pred, Proj proj = {});
template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6 Other range refinements [range.refinements]") R, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6 Other range refinements [range.refinements]") OutR,
          class Proj = identity,
          [indirect_unary_predicate](indirectcallable.indirectinvocable#concept:indirect_unary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<projected<iterator_t<R>, Proj>> Pred>
  requires [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3 Concept indirectly_­copyable [alg.req.ind.copy]")<iterator_t<R>, iterator_t<OutR>>
  ranges::copy_if_result<borrowed_iterator_t<R>, borrowed_iterator_t<OutR>>
    ranges::copy_if(Ep&& exec, R&& r, OutR&& result_r, Pred pred, Proj proj = {});
`

[19](#alg.copy-19)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6539)

Let E(i) be:

- [(19.1)](#alg.copy-19.1)

bool(pred(*i)) for the overloads in namespace std;

- [(19.2)](#alg.copy-19.2)

bool(invoke(pred, invoke(proj, *i))) for the overloads in namespace ranges[.](#alg.copy-19.sentence-1)

[20](#alg.copy-20)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6550)

Let:

- [(20.1)](#alg.copy-20.1)

M be the number of iterators i in the range [first, last)
 for which the condition E(i) holds;

- [(20.2)](#alg.copy-20.2)

result_last be result + M for the overloads with no parameter result_last or result_r;

- [(20.3)](#alg.copy-20.3)

N be min(M, result_last - result)[.](#alg.copy-20.sentence-1)

[21](#alg.copy-21)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6563)

*Preconditions*: The ranges [first, last) and [result, result + N)
do not overlap[.](#alg.copy-21.sentence-1)

[*Note [1](#alg.copy-note-1)*:

For the parallel algorithm overload in namespace std,
there can be a performance cost
if iterator_traits<ForwardIterator1>​::​value_type does not meet the *Cpp17MoveConstructible* (Table [31](utility.arg.requirements#tab:cpp17.moveconstructible "Table 31: Cpp17MoveConstructible requirements")) requirements[.](#alg.copy-21.sentence-2)

For the parallel algorithm overloads in namespace ranges,
there can be a performance cost
if iter_value_t<I> does not model [move_constructible](concept.moveconstructible#concept:move_constructible "18.4.13 Concept move_­constructible [concept.moveconstructible]")[.](#alg.copy-21.sentence-3)

— *end note*]

[22](#alg.copy-22)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6577)

*Effects*: Copies the first N elements referred to
by the iterator i in the range [first, last)
for which E(i) is true into the range [result, result + N)[.](#alg.copy-22.sentence-1)

[23](#alg.copy-23)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6584)

*Returns*: 

- [(23.1)](#alg.copy-23.1)

  result + N for the overloads in namespace std[.](#alg.copy-23.1.sentence-1)

- [(23.2)](#alg.copy-23.2)

  {last, result + N} for the overloads in namespace ranges, if N is equal to M[.](#alg.copy-23.2.sentence-1)

- [(23.3)](#alg.copy-23.3)

  Otherwise, {j, result_last} for the overloads in namespace ranges,
 where j is the iterator in [first, last)
 for which E(j) holds
 and there are exactly N iterators i in [first, j) for which E(i) holds[.](#alg.copy-23.3.sentence-1)

[24](#alg.copy-24)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6602)

*Complexity*: At most last - first applications
of the corresponding predicate and any projection[.](#alg.copy-24.sentence-1)

[25](#alg.copy-25)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6607)

*Remarks*: Stable ([[algorithm.stable]](algorithm.stable "16.4.6.8 Requirements for stable algorithms"))[.](#alg.copy-25.sentence-1)

[🔗](#lib:copy_backward)

`template<class BidirectionalIterator1, class BidirectionalIterator2>
  constexpr BidirectionalIterator2
    copy_backward(BidirectionalIterator1 first,
                  BidirectionalIterator1 last,
                  BidirectionalIterator2 result);

template<[bidirectional_iterator](iterator.concept.bidir#concept:bidirectional_iterator "24.3.4.12 Concept bidirectional_­iterator [iterator.concept.bidir]") I1, [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7 Concept sentinel_­for [iterator.concept.sentinel]")<I1> S1, [bidirectional_iterator](iterator.concept.bidir#concept:bidirectional_iterator "24.3.4.12 Concept bidirectional_­iterator [iterator.concept.bidir]") I2>
  requires [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3 Concept indirectly_­copyable [alg.req.ind.copy]")<I1, I2>
  constexpr ranges::copy_backward_result<I1, I2>
    ranges::copy_backward(I1 first, S1 last, I2 result);
template<[bidirectional_range](range.refinements#concept:bidirectional_range "25.4.6 Other range refinements [range.refinements]") R, [bidirectional_iterator](iterator.concept.bidir#concept:bidirectional_iterator "24.3.4.12 Concept bidirectional_­iterator [iterator.concept.bidir]") I>
  requires [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3 Concept indirectly_­copyable [alg.req.ind.copy]")<iterator_t<R>, I>
  constexpr ranges::copy_backward_result<borrowed_iterator_t<R>, I>
    ranges::copy_backward(R&& r, I result);
`

[26](#alg.copy-26)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6631)

Let N be last - first[.](#alg.copy-26.sentence-1)

[27](#alg.copy-27)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6634)

*Preconditions*: result is not in the range (first, last][.](#alg.copy-27.sentence-1)

[28](#alg.copy-28)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6638)

*Effects*: Copies elements in the range [first, last)
into the range [result - N, result)
starting from last - 1 and proceeding to first[.](#alg.copy-28.sentence-1)[201](#footnote-201 "copy_­backward can be used instead of copy when last is in the range [result - N, result).")

For each positive integer n ≤ N,
performs *(result - n) = *(last - n)[.](#alg.copy-28.sentence-2)

[29](#alg.copy-29)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6650)

*Returns*: 

- [(29.1)](#alg.copy-29.1)

  result - N for the overload in namespace std[.](#alg.copy-29.1.sentence-1)

- [(29.2)](#alg.copy-29.2)

  {last, result - N} for the overloads in namespace ranges[.](#alg.copy-29.2.sentence-1)

[30](#alg.copy-30)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6661)

*Complexity*: Exactly N assignments[.](#alg.copy-30.sentence-1)

[201)](#footnote-201)[201)](#footnoteref-201)

copy_backward can be used instead of copy when last is in the range [result - N, result)[.](#footnote-201.sentence-1)

### [26.7.2](#alg.move) Move [[alg.move]](alg.move)

[🔗](#lib:move,algorithm)

`template<class InputIterator, class OutputIterator>
  constexpr OutputIterator move(InputIterator first, InputIterator last,
                                OutputIterator result);

template<[input_iterator](iterator.concept.input#concept:input_iterator "24.3.4.9 Concept input_­iterator [iterator.concept.input]") I, [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7 Concept sentinel_­for [iterator.concept.sentinel]")<I> S, [weakly_incrementable](iterator.concept.winc#concept:weakly_incrementable "24.3.4.4 Concept weakly_­incrementable [iterator.concept.winc]") O>
  requires [indirectly_movable](alg.req.ind.move#concept:indirectly_movable "24.3.7.2 Concept indirectly_­movable [alg.req.ind.move]")<I, O>
  constexpr ranges::move_result<I, O>
    ranges::move(I first, S last, O result);
template<[input_range](range.refinements#concept:input_range "25.4.6 Other range refinements [range.refinements]") R, [weakly_incrementable](iterator.concept.winc#concept:weakly_incrementable "24.3.4.4 Concept weakly_­incrementable [iterator.concept.winc]") O>
  requires [indirectly_movable](alg.req.ind.move#concept:indirectly_movable "24.3.7.2 Concept indirectly_­movable [alg.req.ind.move]")<iterator_t<R>, O>
  constexpr ranges::move_result<borrowed_iterator_t<R>, O>
    ranges::move(R&& r, O result);
`

[1](#alg.move-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6685)

Let E(n) be

- [(1.1)](#alg.move-1.1)

std​::​move(*(first + n)) for the overload in namespace std;

- [(1.2)](#alg.move-1.2)

ranges​::​iter_move(first + n) for the overloads in namespace ranges[.](#alg.move-1.sentence-1)

Let N be last - first[.](#alg.move-1.sentence-2)

[2](#alg.move-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6697)

*Preconditions*: result is not in the range [first, last)[.](#alg.move-2.sentence-1)

[3](#alg.move-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6701)

*Effects*: Moves elements in the range [first, last)
into the range [result, result + N)
starting from first and proceeding to last[.](#alg.move-3.sentence-1)

For each non-negative integer n<N, performs *(result + n) = E(n)[.](#alg.move-3.sentence-2)

[4](#alg.move-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6708)

*Returns*: 

- [(4.1)](#alg.move-4.1)

  result + N for the overload in namespace std[.](#alg.move-4.1.sentence-1)

- [(4.2)](#alg.move-4.2)

  {last, result + N} for the overloads in namespace ranges[.](#alg.move-4.2.sentence-1)

[5](#alg.move-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6719)

*Complexity*: Exactly N assignments[.](#alg.move-5.sentence-1)

[🔗](#lib:move,algorithm_)

`template<class ExecutionPolicy, class ForwardIterator1, class ForwardIterator2>
  ForwardIterator2 move(ExecutionPolicy&& exec,
                        ForwardIterator1 first, ForwardIterator1 last,
                        ForwardIterator2 result);

template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]") I, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<I> S,
         [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]") O, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<O> OutS>
  requires [indirectly_movable](alg.req.ind.move#concept:indirectly_movable "24.3.7.2 Concept indirectly_­movable [alg.req.ind.move]")<I, O>
  ranges::move_result<I, O>
    ranges::move(Ep&& exec, I first, S last, O result, OutS result_last);
template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6 Other range refinements [range.refinements]") R, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6 Other range refinements [range.refinements]") OutR>
  requires [indirectly_movable](alg.req.ind.move#concept:indirectly_movable "24.3.7.2 Concept indirectly_­movable [alg.req.ind.move]")<iterator_t<R>, iterator_t<OutR>>
  ranges::move_result<borrowed_iterator_t<R>, borrowed_iterator_t<OutR>>
    ranges::move(Ep&& exec, R&& r, OutR&& result_r);
`

[6](#alg.move-6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6743)

Let E(n) be:

- [(6.1)](#alg.move-6.1)

std​::​move(*(first + n)) for the overload in namespace std;

- [(6.2)](#alg.move-6.2)

ranges​::​iter_move(first + n) for the overloads in namespace ranges[.](#alg.move-6.sentence-1)

[7](#alg.move-7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6754)

Let result_last be result + (last - first) for the overloads in namespace std[.](#alg.move-7.sentence-1)

[8](#alg.move-8)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6758)

Let N be min(last - first, result_last - result)[.](#alg.move-8.sentence-1)

[9](#alg.move-9)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6761)

*Preconditions*: The ranges [first, last) and [result, result + N)
do not overlap[.](#alg.move-9.sentence-1)

[10](#alg.move-10)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6766)

*Effects*: Moves elements in the range [first, first + N)
into the range [result, result + N)[.](#alg.move-10.sentence-1)

For each non-negative integer n<N,
performs *(result + n) = E(n)[.](#alg.move-10.sentence-2)

[11](#alg.move-11)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6773)

*Returns*: 

- [(11.1)](#alg.move-11.1)

  result + N for the overload in namespace std[.](#alg.move-11.1.sentence-1)

- [(11.2)](#alg.move-11.2)

  {first + N, result + N} for the overloads in namespace ranges[.](#alg.move-11.2.sentence-1)

[12](#alg.move-12)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6784)

*Complexity*: Exactly N assignments[.](#alg.move-12.sentence-1)

[🔗](#lib:move_backward)

`template<class BidirectionalIterator1, class BidirectionalIterator2>
  constexpr BidirectionalIterator2
    move_backward(BidirectionalIterator1 first, BidirectionalIterator1 last,
                  BidirectionalIterator2 result);

template<[bidirectional_iterator](iterator.concept.bidir#concept:bidirectional_iterator "24.3.4.12 Concept bidirectional_­iterator [iterator.concept.bidir]") I1, [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7 Concept sentinel_­for [iterator.concept.sentinel]")<I1> S1, [bidirectional_iterator](iterator.concept.bidir#concept:bidirectional_iterator "24.3.4.12 Concept bidirectional_­iterator [iterator.concept.bidir]") I2>
  requires [indirectly_movable](alg.req.ind.move#concept:indirectly_movable "24.3.7.2 Concept indirectly_­movable [alg.req.ind.move]")<I1, I2>
  constexpr ranges::move_backward_result<I1, I2>
    ranges::move_backward(I1 first, S1 last, I2 result);
template<[bidirectional_range](range.refinements#concept:bidirectional_range "25.4.6 Other range refinements [range.refinements]") R, [bidirectional_iterator](iterator.concept.bidir#concept:bidirectional_iterator "24.3.4.12 Concept bidirectional_­iterator [iterator.concept.bidir]") I>
  requires [indirectly_movable](alg.req.ind.move#concept:indirectly_movable "24.3.7.2 Concept indirectly_­movable [alg.req.ind.move]")<iterator_t<R>, I>
  constexpr ranges::move_backward_result<borrowed_iterator_t<R>, I>
    ranges::move_backward(R&& r, I result);
`

[13](#alg.move-13)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6807)

Let E(n) be

- [(13.1)](#alg.move-13.1)

std​::​move(*(last - n)) for the overload in namespace std;

- [(13.2)](#alg.move-13.2)

ranges​::​iter_move(last - n) for the overloads in namespace ranges[.](#alg.move-13.sentence-1)

Let N be last - first[.](#alg.move-13.sentence-2)

[14](#alg.move-14)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6819)

*Preconditions*: result is not in the range (first, last][.](#alg.move-14.sentence-1)

[15](#alg.move-15)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6823)

*Effects*: Moves elements in the range [first, last)
into the range [result - N, result)
starting from last - 1 and proceeding to first[.](#alg.move-15.sentence-1)[202](#footnote-202 "move_­backward can be used instead of move when last is in the range [result - N, result).")

For each positive integer n ≤ N,
performs *(result - n) = E(n)[.](#alg.move-15.sentence-2)

[16](#alg.move-16)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6835)

*Returns*: 

- [(16.1)](#alg.move-16.1)

  result - N for the overload in namespace std[.](#alg.move-16.1.sentence-1)

- [(16.2)](#alg.move-16.2)

  {last, result - N} for the overloads in namespace ranges[.](#alg.move-16.2.sentence-1)

[17](#alg.move-17)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6846)

*Complexity*: Exactly N assignments[.](#alg.move-17.sentence-1)

[202)](#footnote-202)[202)](#footnoteref-202)

move_backward can be used instead of move when last is in the range [result - N, result)[.](#footnote-202.sentence-1)

### [26.7.3](#alg.swap) Swap [[alg.swap]](alg.swap)

[🔗](#lib:swap_ranges)

`template<class ForwardIterator1, class ForwardIterator2>
  constexpr ForwardIterator2
    swap_ranges(ForwardIterator1 first1, ForwardIterator1 last1,
                ForwardIterator2 first2);
template<class ExecutionPolicy, class ForwardIterator1, class ForwardIterator2>
  ForwardIterator2
    swap_ranges(ExecutionPolicy&& exec,
                ForwardIterator1 first1, ForwardIterator1 last1,
                ForwardIterator2 first2);

template<[input_iterator](iterator.concept.input#concept:input_iterator "24.3.4.9 Concept input_­iterator [iterator.concept.input]") I1, [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7 Concept sentinel_­for [iterator.concept.sentinel]")<I1> S1, [input_iterator](iterator.concept.input#concept:input_iterator "24.3.4.9 Concept input_­iterator [iterator.concept.input]") I2, [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7 Concept sentinel_­for [iterator.concept.sentinel]")<I2> S2>
  requires [indirectly_swappable](alg.req.ind.swap#concept:indirectly_swappable "24.3.7.4 Concept indirectly_­swappable [alg.req.ind.swap]")<I1, I2>
  constexpr ranges::swap_ranges_result<I1, I2>
    ranges::swap_ranges(I1 first1, S1 last1, I2 first2, S2 last2);
template<[input_range](range.refinements#concept:input_range "25.4.6 Other range refinements [range.refinements]") R1, [input_range](range.refinements#concept:input_range "25.4.6 Other range refinements [range.refinements]") R2>
  requires [indirectly_swappable](alg.req.ind.swap#concept:indirectly_swappable "24.3.7.4 Concept indirectly_­swappable [alg.req.ind.swap]")<iterator_t<R1>, iterator_t<R2>>
  constexpr ranges::swap_ranges_result<borrowed_iterator_t<R1>, borrowed_iterator_t<R2>>
    ranges::swap_ranges(R1&& r1, R2&& r2);

template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]") I1, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<I1> S1,
         [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]") I2, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<I2> S2>
  requires [indirectly_swappable](alg.req.ind.swap#concept:indirectly_swappable "24.3.7.4 Concept indirectly_­swappable [alg.req.ind.swap]")<I1, I2>
  ranges::swap_ranges_result<I1, I2>
    ranges::swap_ranges(Ep&& exec, I1 first1, S1 last1, I2 first2, S2 last2);
template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6 Other range refinements [range.refinements]") R1, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6 Other range refinements [range.refinements]") R2>
  requires [indirectly_swappable](alg.req.ind.swap#concept:indirectly_swappable "24.3.7.4 Concept indirectly_­swappable [alg.req.ind.swap]")<iterator_t<R1>, iterator_t<R2>>
  ranges::swap_ranges_result<borrowed_iterator_t<R1>, borrowed_iterator_t<R2>>
    ranges::swap_ranges(Ep&& exec, R1&& r1, R2&& r2);
`

[1](#alg.swap-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6886)

Let:

- [(1.1)](#alg.swap-1.1)

last2 be first2 + (last1 - first1) for the overloads in namespace std with no parameter named last2;

- [(1.2)](#alg.swap-1.2)

M be min(last1 - first1, last2 - first2)[.](#alg.swap-1.sentence-1)

[2](#alg.swap-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6896)

*Preconditions*: The two ranges [first1, last1) and [first2, last2)
do not overlap[.](#alg.swap-2.sentence-1)

For the overloads in namespace std,*(first1 + n) is swappable with ([[swappable.requirements]](swappable.requirements "16.4.4.3 Swappable requirements"))*(first2 + n)[.](#alg.swap-2.sentence-2)

[3](#alg.swap-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6904)

*Effects*: For each non-negative integer n<M performs:

- [(3.1)](#alg.swap-3.1)

swap(*(first1 + n), *(first2 + n)) for the overloads in namespace std;

- [(3.2)](#alg.swap-3.2)

ranges​::​iter_swap(first1 + n, first2 + n) for the overloads in namespace ranges[.](#alg.swap-3.sentence-1)

[4](#alg.swap-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6916)

*Returns*: 

- [(4.1)](#alg.swap-4.1)

  last2 for the overloads in namespace std[.](#alg.swap-4.1.sentence-1)

- [(4.2)](#alg.swap-4.2)

  {first1 + M, first2 + M} for the overloads in namespace ranges[.](#alg.swap-4.2.sentence-1)

[5](#alg.swap-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6927)

*Complexity*: Exactly M swaps[.](#alg.swap-5.sentence-1)

[🔗](#lib:iter_swap)

`template<class ForwardIterator1, class ForwardIterator2>
  constexpr void iter_swap(ForwardIterator1 a, ForwardIterator2 b);
`

[6](#alg.swap-6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6939)

*Preconditions*: a and b are dereferenceable[.](#alg.swap-6.sentence-1)

*a is
swappable with ([[swappable.requirements]](swappable.requirements "16.4.4.3 Swappable requirements")) *b[.](#alg.swap-6.sentence-2)

[7](#alg.swap-7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L6944)

*Effects*: As if by swap(*a, *b)[.](#alg.swap-7.sentence-1)

### [26.7.4](#alg.transform) Transform [[alg.transform]](alg.transform)

[🔗](#lib:transform)

`template<class InputIterator, class OutputIterator,
         class UnaryOperation>
  constexpr OutputIterator
    transform(InputIterator first1, InputIterator last1,
              OutputIterator result, UnaryOperation op);
template<class ExecutionPolicy, class ForwardIterator1, class ForwardIterator2,
         class UnaryOperation>
  ForwardIterator2
    transform(ExecutionPolicy&& exec,
              ForwardIterator1 first1, ForwardIterator1 last1,
              ForwardIterator2 result, UnaryOperation op);

template<class InputIterator1, class InputIterator2,
         class OutputIterator, class BinaryOperation>
  constexpr OutputIterator
    transform(InputIterator1 first1, InputIterator1 last1,
              InputIterator2 first2, OutputIterator result,
              BinaryOperation binary_op);
template<class ExecutionPolicy, class ForwardIterator1, class ForwardIterator2,
         class ForwardIterator, class BinaryOperation>
  ForwardIterator
    transform(ExecutionPolicy&& exec,
              ForwardIterator1 first1, ForwardIterator1 last1,
              ForwardIterator2 first2, ForwardIterator result,
              BinaryOperation binary_op);

template<[input_iterator](iterator.concept.input#concept:input_iterator "24.3.4.9 Concept input_­iterator [iterator.concept.input]") I, [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7 Concept sentinel_­for [iterator.concept.sentinel]")<I> S, [weakly_incrementable](iterator.concept.winc#concept:weakly_incrementable "24.3.4.4 Concept weakly_­incrementable [iterator.concept.winc]") O,
         [copy_constructible](concept.copyconstructible#concept:copy_constructible "18.4.14 Concept copy_­constructible [concept.copyconstructible]") F, class Proj = identity>
  requires [indirectly_writable](iterator.concept.writable#concept:indirectly_writable "24.3.4.3 Concept indirectly_­writable [iterator.concept.writable]")<O, indirect_result_t<F&, projected<I, Proj>>>
  constexpr ranges::unary_transform_result<I, O>
    ranges::transform(I first1, S last1, O result, F op, Proj proj = {});
template<[input_range](range.refinements#concept:input_range "25.4.6 Other range refinements [range.refinements]") R, [weakly_incrementable](iterator.concept.winc#concept:weakly_incrementable "24.3.4.4 Concept weakly_­incrementable [iterator.concept.winc]") O, [copy_constructible](concept.copyconstructible#concept:copy_constructible "18.4.14 Concept copy_­constructible [concept.copyconstructible]") F,
         class Proj = identity>
  requires [indirectly_writable](iterator.concept.writable#concept:indirectly_writable "24.3.4.3 Concept indirectly_­writable [iterator.concept.writable]")<O, indirect_result_t<F&, projected<iterator_t<R>, Proj>>>
  constexpr ranges::unary_transform_result<borrowed_iterator_t<R>, O>
    ranges::transform(R&& r, O result, F op, Proj proj = {});

template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]") I, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<I> S,
         [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]") O, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<O> OutS,
         [copy_constructible](concept.copyconstructible#concept:copy_constructible "18.4.14 Concept copy_­constructible [concept.copyconstructible]") F, class Proj = identity>
  requires [indirectly_writable](iterator.concept.writable#concept:indirectly_writable "24.3.4.3 Concept indirectly_­writable [iterator.concept.writable]")<O, indirect_result_t<F&, projected<I, Proj>>>
  ranges::unary_transform_result<I, O>
    ranges::transform(Ep&& exec, I first1, S last1, O result, OutS result_last,
                      F op, Proj proj = {});
template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6 Other range refinements [range.refinements]") R, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6 Other range refinements [range.refinements]") OutR,
          [copy_constructible](concept.copyconstructible#concept:copy_constructible "18.4.14 Concept copy_­constructible [concept.copyconstructible]") F, class Proj = identity>
  requires [indirectly_writable](iterator.concept.writable#concept:indirectly_writable "24.3.4.3 Concept indirectly_­writable [iterator.concept.writable]")<iterator_t<OutR>,
                                indirect_result_t<F&, projected<iterator_t<R>, Proj>>>
  ranges::unary_transform_result<borrowed_iterator_t<R>, borrowed_iterator_t<OutR>>
    ranges::transform(Ep&& exec, R&& r, OutR&& result_r, F op, Proj proj = {});

template<[input_iterator](iterator.concept.input#concept:input_iterator "24.3.4.9 Concept input_­iterator [iterator.concept.input]") I1, [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7 Concept sentinel_­for [iterator.concept.sentinel]")<I1> S1, [input_iterator](iterator.concept.input#concept:input_iterator "24.3.4.9 Concept input_­iterator [iterator.concept.input]") I2, [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7 Concept sentinel_­for [iterator.concept.sentinel]")<I2> S2,
         [weakly_incrementable](iterator.concept.winc#concept:weakly_incrementable "24.3.4.4 Concept weakly_­incrementable [iterator.concept.winc]") O, [copy_constructible](concept.copyconstructible#concept:copy_constructible "18.4.14 Concept copy_­constructible [concept.copyconstructible]") F, class Proj1 = identity,
         class Proj2 = identity>
  requires [indirectly_writable](iterator.concept.writable#concept:indirectly_writable "24.3.4.3 Concept indirectly_­writable [iterator.concept.writable]")<O, indirect_result_t<F&, projected<I1, Proj1>,
                               projected<I2, Proj2>>>
  constexpr ranges::binary_transform_result<I1, I2, O>
    ranges::transform(I1 first1, S1 last1, I2 first2, S2 last2, O result,
                      F binary_op, Proj1 proj1 = {}, Proj2 proj2 = {});
template<[input_range](range.refinements#concept:input_range "25.4.6 Other range refinements [range.refinements]") R1, [input_range](range.refinements#concept:input_range "25.4.6 Other range refinements [range.refinements]") R2, [weakly_incrementable](iterator.concept.winc#concept:weakly_incrementable "24.3.4.4 Concept weakly_­incrementable [iterator.concept.winc]") O,
         [copy_constructible](concept.copyconstructible#concept:copy_constructible "18.4.14 Concept copy_­constructible [concept.copyconstructible]") F, class Proj1 = identity, class Proj2 = identity>
  requires [indirectly_writable](iterator.concept.writable#concept:indirectly_writable "24.3.4.3 Concept indirectly_­writable [iterator.concept.writable]")<O, indirect_result_t<F&, projected<iterator_t<R1>, Proj1>,
                               projected<iterator_t<R2>, Proj2>>>
  constexpr ranges::binary_transform_result<borrowed_iterator_t<R1>, borrowed_iterator_t<R2>, O>
    ranges::transform(R1&& r1, R2&& r2, O result,
                      F binary_op, Proj1 proj1 = {}, Proj2 proj2 = {});

template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]") I1, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<I1> S1,
         [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]") I2, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<I2> S2,
         [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]") O, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<O> OutS,
         [copy_constructible](concept.copyconstructible#concept:copy_constructible "18.4.14 Concept copy_­constructible [concept.copyconstructible]") F, class Proj1 = identity, class Proj2 = identity>
  requires [indirectly_writable](iterator.concept.writable#concept:indirectly_writable "24.3.4.3 Concept indirectly_­writable [iterator.concept.writable]")<O, indirect_result_t<F&, projected<I1, Proj1>,
                                projected<I2, Proj2>>>
  ranges::binary_transform_result<I1, I2, O>
    ranges::transform(Ep&& exec, I1 first1, S1 last1, I2 first2, S2 last2,
                      O result, OutS result_last,
                      F binary_op, Proj1 proj1 = {}, Proj2 proj2 = {});
template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6 Other range refinements [range.refinements]") R1, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6 Other range refinements [range.refinements]") R2,
         [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6 Other range refinements [range.refinements]") OutR, [copy_constructible](concept.copyconstructible#concept:copy_constructible "18.4.14 Concept copy_­constructible [concept.copyconstructible]") F,
          class Proj1 = identity, class Proj2 = identity>
  requires [indirectly_writable](iterator.concept.writable#concept:indirectly_writable "24.3.4.3 Concept indirectly_­writable [iterator.concept.writable]")<iterator_t<OutR>,
                                indirect_result_t<F&, projected<iterator_t<R1>, Proj1>,
                                projected<iterator_t<R2>, Proj2>>>
  ranges::binary_transform_result<borrowed_iterator_t<R1>, borrowed_iterator_t<R2>,
                                  borrowed_iterator_t<OutR>>
    ranges::transform(Ep&& exec, R1&& r1, R2&& r2, OutR&& result_r,
                      F binary_op, Proj1 proj1 = {}, Proj2 proj2 = {});
`

[1](#alg.transform-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7043)

Let:

- [(1.1)](#alg.transform-1.1)

last2 be first2 + (last1 - first1) for the overloads in namespace std with parameter first2 but no parameter last2;

- [(1.2)](#alg.transform-1.2)

M be last1 - first1 for unary transforms, or min(last1 - first1, last2 - first2) for binary transforms;

- [(1.3)](#alg.transform-1.3)

result_last be result + M for the overloads with no parameter result_last or result_r;

- [(1.4)](#alg.transform-1.4)

N be min(M, result_last - result);

- [(1.5)](#alg.transform-1.5)

E(i) be
  * [(1.5.1)](#alg.transform-1.5.1)

op(*(first1 + (i - result))) for unary transforms defined in namespace std;

  * [(1.5.2)](#alg.transform-1.5.2)

binary_op(*(first1 + (i - result)), *(first2 + (i - result))) for binary transforms defined in namespace std;

  * [(1.5.3)](#alg.transform-1.5.3)

invoke(op, invoke(proj, *(first1 + (i - result)))) for unary transforms defined in namespace ranges;

  * [(1.5.4)](#alg.transform-1.5.4)

invoke(binary_op, invoke(proj1, *(first1 + (i - result))), invoke(proj2, *(first2 + (i - result)))) for binary transforms defined in namespace ranges[.](#alg.transform-1.sentence-1)

[2](#alg.transform-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7078)

*Preconditions*: For parallel algorithm overloadsop and binary_op satisfy the requirements
specified in [[algorithms.parallel.user]](algorithms.parallel.user "26.3.2 Requirements on user-provided function objects")[.](#alg.transform-2.sentence-1)

op and binary_op do not invalidate iterators or subranges, nor
modify elements in the ranges

- [(2.1)](#alg.transform-2.1)

[first1, first1 + N],

- [(2.2)](#alg.transform-2.2)

[first2, first2 + N], and

- [(2.3)](#alg.transform-2.3)

[result, result + N][.](#alg.transform-2.sentence-2)[203](#footnote-203 "The use of fully closed ranges is intentional.")

[3](#alg.transform-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7094)

*Effects*: Assigns through every iterator i in the range [result, result + N)
a new corresponding value equal to E(i)[.](#alg.transform-3.sentence-1)

[4](#alg.transform-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7100)

*Returns*: 

- [(4.1)](#alg.transform-4.1)

  result + N for the overloads defined in namespace std[.](#alg.transform-4.1.sentence-1)

- [(4.2)](#alg.transform-4.2)

  {first1 + N, result + N} for unary transforms defined in namespace ranges[.](#alg.transform-4.2.sentence-1)

- [(4.3)](#alg.transform-4.3)

  {first1 + N, first2 + N, result + N} for binary transforms defined in namespace ranges[.](#alg.transform-4.3.sentence-1)

[5](#alg.transform-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7114)

*Complexity*: Exactly N applications of op or binary_op, and
any projections[.](#alg.transform-5.sentence-1)

This requirement also applies to the parallel algorithm overloads[.](#alg.transform-5.sentence-2)

[6](#alg.transform-6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7120)

*Remarks*: result may be equal to first1 or first2[.](#alg.transform-6.sentence-1)

[203)](#footnote-203)[203)](#footnoteref-203)

The use of fully closed ranges is intentional[.](#footnote-203.sentence-1)

### [26.7.5](#alg.replace) Replace [[alg.replace]](alg.replace)

[🔗](#lib:replace)

`template<class ForwardIterator, class T = iterator_traits<ForwardIterator>::value_type>
  constexpr void replace(ForwardIterator first, ForwardIterator last,
                         const T& old_value, const T& new_value);
template<class ExecutionPolicy, class ForwardIterator,
         class T = iterator_traits<ForwardIterator>::value_type>
  void replace(ExecutionPolicy&& exec,
               ForwardIterator first, ForwardIterator last,
               const T& old_value, const T& new_value);

template<class ForwardIterator, class Predicate,
         class T = iterator_traits<ForwardIterator>::value_type>
  constexpr void replace_if(ForwardIterator first, ForwardIterator last,
                            Predicate pred, const T& new_value);
template<class ExecutionPolicy, class ForwardIterator, class Predicate,
         class T = iterator_traits<ForwardIterator>::value_type>
  void replace_if(ExecutionPolicy&& exec,
                  ForwardIterator first, ForwardIterator last,
                  Predicate pred, const T& new_value);

template<[input_iterator](iterator.concept.input#concept:input_iterator "24.3.4.9 Concept input_­iterator [iterator.concept.input]") I, [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7 Concept sentinel_­for [iterator.concept.sentinel]")<I> S, class Proj = identity,
         class T1 = projected_value_t<I, Proj>, class T2 = T1>
  requires [indirectly_writable](iterator.concept.writable#concept:indirectly_writable "24.3.4.3 Concept indirectly_­writable [iterator.concept.writable]")<I, const T2&> &&
           [indirect_binary_predicate](indirectcallable.indirectinvocable#concept:indirect_binary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<ranges::equal_to, projected<I, Proj>, const T1*>
  constexpr I
    ranges::replace(I first, S last, const T1& old_value, const T2& new_value, Proj proj = {});
template<[input_range](range.refinements#concept:input_range "25.4.6 Other range refinements [range.refinements]") R, class Proj = identity,
         class T1 = projected_value_t<iterator_t<R>, Proj>, class T2 = T1>
  requires [indirectly_writable](iterator.concept.writable#concept:indirectly_writable "24.3.4.3 Concept indirectly_­writable [iterator.concept.writable]")<iterator_t<R>, const T2&> &&
           [indirect_binary_predicate](indirectcallable.indirectinvocable#concept:indirect_binary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<ranges::equal_to, projected<iterator_t<R>, Proj>, const T1*>
  constexpr borrowed_iterator_t<R>
    ranges::replace(R&& r, const T1& old_value, const T2& new_value, Proj proj = {});

template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]") I, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<I> S,
         class Proj = identity, class T1 = projected_value_t<I, Proj>, class T2 = T1>
  requires [indirectly_writable](iterator.concept.writable#concept:indirectly_writable "24.3.4.3 Concept indirectly_­writable [iterator.concept.writable]")<I, const T2&> &&
           [indirect_binary_predicate](indirectcallable.indirectinvocable#concept:indirect_binary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<ranges::equal_to, projected<I, Proj>, const T1*>
  I ranges::replace(Ep&& exec, I first, S last,
                    const T1& old_value, const T2& new_value, Proj proj = {});
template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6 Other range refinements [range.refinements]") R, class Proj = identity,
         class T1 = projected_value_t<iterator_t<R>, Proj>, class T2 = T1>
  requires [indirectly_writable](iterator.concept.writable#concept:indirectly_writable "24.3.4.3 Concept indirectly_­writable [iterator.concept.writable]")<iterator_t<R>, const T2&> &&
            [indirect_binary_predicate](indirectcallable.indirectinvocable#concept:indirect_binary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<ranges::equal_to,
                                      projected<iterator_t<R>, Proj>, const T1*>
  borrowed_iterator_t<R>
    ranges::replace(Ep&& exec, R&& r, const T1& old_value, const T2& new_value,
                    Proj proj = {});

template<[input_iterator](iterator.concept.input#concept:input_iterator "24.3.4.9 Concept input_­iterator [iterator.concept.input]") I, [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7 Concept sentinel_­for [iterator.concept.sentinel]")<I> S, class Proj = identity,
         class T = projected_value_t<I, Proj>,
         [indirect_unary_predicate](indirectcallable.indirectinvocable#concept:indirect_unary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<projected<I, Proj>> Pred>
  requires [indirectly_writable](iterator.concept.writable#concept:indirectly_writable "24.3.4.3 Concept indirectly_­writable [iterator.concept.writable]")<I, const T&>
  constexpr I ranges::replace_if(I first, S last, Pred pred, const T& new_value, Proj proj = {});
template<[input_range](range.refinements#concept:input_range "25.4.6 Other range refinements [range.refinements]") R, class Proj = identity, class T = projected_value_t<iterator_t<R>, Proj>,
         [indirect_unary_predicate](indirectcallable.indirectinvocable#concept:indirect_unary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<projected<iterator_t<R>, Proj>> Pred>
  requires [indirectly_writable](iterator.concept.writable#concept:indirectly_writable "24.3.4.3 Concept indirectly_­writable [iterator.concept.writable]")<iterator_t<R>, const T&>
  constexpr borrowed_iterator_t<R>
    ranges::replace_if(R&& r, Pred pred, const T& new_value, Proj proj = {});

template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]") I, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<I> S,
         class Proj = identity, class T = projected_value_t<I, Proj>,
         [indirect_unary_predicate](indirectcallable.indirectinvocable#concept:indirect_unary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<projected<I, Proj>> Pred>
  requires [indirectly_writable](iterator.concept.writable#concept:indirectly_writable "24.3.4.3 Concept indirectly_­writable [iterator.concept.writable]")<I, const T&>
  I ranges::replace_if(Ep&& exec, I first, S last, Pred pred,
                       const T& new_value, Proj proj = {});
template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6 Other range refinements [range.refinements]") R, class Proj = identity,
         class T = projected_value_t<iterator_t<R>, Proj>,
         [indirect_unary_predicate](indirectcallable.indirectinvocable#concept:indirect_unary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<projected<iterator_t<R>, Proj>> Pred>
  requires [indirectly_writable](iterator.concept.writable#concept:indirectly_writable "24.3.4.3 Concept indirectly_­writable [iterator.concept.writable]")<iterator_t<R>, const T&>
  borrowed_iterator_t<R>
    ranges::replace_if(Ep&& exec, R&& r, Pred pred, const T& new_value, Proj proj = {});
`

[1](#alg.replace-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7203)

Let E(i) be

- [(1.1)](#alg.replace-1.1)

bool(*i == old_value) for replace;

- [(1.2)](#alg.replace-1.2)

bool(pred(*i)) for replace_if;

- [(1.3)](#alg.replace-1.3)

bool(invoke(proj, *i) == old_value) for ranges​::​replace;

- [(1.4)](#alg.replace-1.4)

bool(invoke(pred, invoke(proj, *i))) for ranges​::​replace_if[.](#alg.replace-1.sentence-1)

[2](#alg.replace-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7212)

*Mandates*: new_value is writable ([[iterator.requirements.general]](iterator.requirements.general "24.3.1 General")) to first[.](#alg.replace-2.sentence-1)

[3](#alg.replace-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7216)

*Effects*: Substitutes elements referred by the iterator i in the range [first, last) with new_value,
when E(i) is true[.](#alg.replace-3.sentence-1)

[4](#alg.replace-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7222)

*Returns*: last for the overloads in namespace ranges[.](#alg.replace-4.sentence-1)

[5](#alg.replace-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7226)

*Complexity*: Exactly last - first applications
of the corresponding predicate and any projection[.](#alg.replace-5.sentence-1)

[🔗](#lib:replace_copy)

`template<class InputIterator, class OutputIterator, class T>
  constexpr OutputIterator
    replace_copy(InputIterator first, InputIterator last,
                 OutputIterator result,
                 const T& old_value, const T& new_value);
template<class ExecutionPolicy, class ForwardIterator1, class ForwardIterator2, class T>
  ForwardIterator2
    replace_copy(ExecutionPolicy&& exec,
                 ForwardIterator1 first, ForwardIterator1 last,
                 ForwardIterator2 result,
                 const T& old_value, const T& new_value);

template<class InputIterator, class OutputIterator, class Predicate, class T>
  constexpr OutputIterator
    replace_copy_if(InputIterator first, InputIterator last,
                    OutputIterator result,
                    Predicate pred, const T& new_value);
template<class ExecutionPolicy, class ForwardIterator1, class ForwardIterator2,
         class Predicate, class T>
  ForwardIterator2
    replace_copy_if(ExecutionPolicy&& exec,
                    ForwardIterator1 first, ForwardIterator1 last,
                    ForwardIterator2 result,
                    Predicate pred, const T& new_value);

template<[input_iterator](iterator.concept.input#concept:input_iterator "24.3.4.9 Concept input_­iterator [iterator.concept.input]") I, [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7 Concept sentinel_­for [iterator.concept.sentinel]")<I> S, class O,
         class Proj = identity, class T1 = projected_value_t<I, Proj>, class T2 = iter_value_t<O>>
  requires [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3 Concept indirectly_­copyable [alg.req.ind.copy]")<I, O> &&
           [indirect_binary_predicate](indirectcallable.indirectinvocable#concept:indirect_binary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<ranges::equal_to, projected<I, Proj>, const T1*> &&
           [output_iterator](iterator.concept.output#concept:output_iterator "24.3.4.10 Concept output_­iterator [iterator.concept.output]")<O, const T2&>
  constexpr ranges::replace_copy_result<I, O>
    ranges::replace_copy(I first, S last, O result, const T1& old_value, const T2& new_value,
                         Proj proj = {});
template<[input_range](range.refinements#concept:input_range "25.4.6 Other range refinements [range.refinements]") R, class O, class Proj = identity,
         class T1 = projected_value_t<iterator_t<R>, Proj>, class T2 = iter_value_t<O>>
  requires [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3 Concept indirectly_­copyable [alg.req.ind.copy]")<iterator_t<R>, O> &&
           [indirect_binary_predicate](indirectcallable.indirectinvocable#concept:indirect_binary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<ranges::equal_to, projected<iterator_t<R>, Proj>, const T1*>
           && [output_iterator](iterator.concept.output#concept:output_iterator "24.3.4.10 Concept output_­iterator [iterator.concept.output]")<O, const T2&>
  constexpr ranges::replace_copy_result<borrowed_iterator_t<R>, O>
    ranges::replace_copy(R&& r, O result, const T1& old_value, const T2& new_value,
                         Proj proj = {});

template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]") I, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<I> S,
         [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]") O, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<O> OutS,
         class Proj = identity,
         class T1 = projected_value_t<I, Proj>, class T2 = iter_value_t<O>>
  requires [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3 Concept indirectly_­copyable [alg.req.ind.copy]")<I, O> &&
           [indirect_binary_predicate](indirectcallable.indirectinvocable#concept:indirect_binary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<ranges::equal_to, projected<I, Proj>, const T1*> &&
           [indirectly_writable](iterator.concept.writable#concept:indirectly_writable "24.3.4.3 Concept indirectly_­writable [iterator.concept.writable]")<O, const T2&>
  ranges::replace_copy_result<I, O>
    ranges::replace_copy(Ep&& exec, I first, S last, O result, OutS result_last,
                         const T1& old_value, const T2& new_value, Proj proj = {});
template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6 Other range refinements [range.refinements]") R, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6 Other range refinements [range.refinements]") OutR,
         class Proj = identity, class T1 = projected_value_t<iterator_t<R>, Proj>,
         class T2 = range_value_t<OutR>>
  requires [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3 Concept indirectly_­copyable [alg.req.ind.copy]")<iterator_t<R>, iterator_t<OutR>> &&
           [indirect_binary_predicate](indirectcallable.indirectinvocable#concept:indirect_binary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<ranges::equal_to,
                                      projected<iterator_t<R>, Proj>, const T1*> &&
           [indirectly_writable](iterator.concept.writable#concept:indirectly_writable "24.3.4.3 Concept indirectly_­writable [iterator.concept.writable]")<iterator_t<OutR>, const T2&>
  ranges::replace_copy_result<borrowed_iterator_t<R>, borrowed_iterator_t<OutR>>
    ranges::replace_copy(Ep&& exec, R&& r, OutR&& result_r, const T1& old_value,
                         const T2& new_value, Proj proj = {});

template<[input_iterator](iterator.concept.input#concept:input_iterator "24.3.4.9 Concept input_­iterator [iterator.concept.input]") I, [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7 Concept sentinel_­for [iterator.concept.sentinel]")<I> S,class O, class T = iter_value_t<O>,
         class Proj = identity, [indirect_unary_predicate](indirectcallable.indirectinvocable#concept:indirect_unary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<projected<I, Proj>> Pred>
  requires [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3 Concept indirectly_­copyable [alg.req.ind.copy]")<I, O> && [output_iterator](iterator.concept.output#concept:output_iterator "24.3.4.10 Concept output_­iterator [iterator.concept.output]")<O, const T&>
  constexpr ranges::replace_copy_if_result<I, O>
    ranges::replace_copy_if(I first, S last, O result, Pred pred, const T& new_value,
                            Proj proj = {});
template<[input_range](range.refinements#concept:input_range "25.4.6 Other range refinements [range.refinements]") R, class O, class T = iter_value_t<O>, class Proj = identity,
         [indirect_unary_predicate](indirectcallable.indirectinvocable#concept:indirect_unary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<projected<iterator_t<R>, Proj>> Pred>
  requires [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3 Concept indirectly_­copyable [alg.req.ind.copy]")<iterator_t<R>, O> && [output_iterator](iterator.concept.output#concept:output_iterator "24.3.4.10 Concept output_­iterator [iterator.concept.output]")<O, const T&>
  constexpr ranges::replace_copy_if_result<borrowed_iterator_t<R>, O>
    ranges::replace_copy_if(R&& r, O result, Pred pred, const T& new_value,
                            Proj proj = {});

template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]") I, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<I> S,
         [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]") O, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<O> OutS, class T = iter_value_t<O>,
         class Proj = identity, [indirect_unary_predicate](indirectcallable.indirectinvocable#concept:indirect_unary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<projected<I, Proj>> Pred>
  requires [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3 Concept indirectly_­copyable [alg.req.ind.copy]")<I, O> && [indirectly_writable](iterator.concept.writable#concept:indirectly_writable "24.3.4.3 Concept indirectly_­writable [iterator.concept.writable]")<O, const T&>
  ranges::replace_copy_if_result<I, O>
    ranges::replace_copy_if(Ep&& exec, I first, S last, O result, OutS result_last,
                            Pred pred, const T& new_value, Proj proj = {});
template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6 Other range refinements [range.refinements]") R, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6 Other range refinements [range.refinements]") OutR,
         class T = range_value_t<OutR>, class Proj = identity,
         [indirect_unary_predicate](indirectcallable.indirectinvocable#concept:indirect_unary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<projected<iterator_t<R>, Proj>> Pred>
  requires [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3 Concept indirectly_­copyable [alg.req.ind.copy]")<iterator_t<R>, iterator_t<OutR>> &&
           [indirectly_writable](iterator.concept.writable#concept:indirectly_writable "24.3.4.3 Concept indirectly_­writable [iterator.concept.writable]")<OutR, const T&>
  ranges::replace_copy_if_result<borrowed_iterator_t<R>, borrowed_iterator_t<OutR>>
    ranges::replace_copy_if(Ep&& exec, R&& r, OutR&& result_r, Pred pred, const T& new_value,
                            Proj proj = {});
`

[6](#alg.replace-6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7330)

Let E(i) be

- [(6.1)](#alg.replace-6.1)

bool(*(first + (i - result)) == old_value) for replace_copy;

- [(6.2)](#alg.replace-6.2)

bool(pred(*(first + (i - result)))) for replace_copy_if;

- [(6.3)](#alg.replace-6.3)

bool(invoke(proj, *(first + (i - result))) == old_value) for ranges​::​replace_copy;

- [(6.4)](#alg.replace-6.4)

bool(invoke(pred, invoke(proj, *(first + (i - result))))) for ranges​::​replace_copy_if[.](#alg.replace-6.sentence-1)

[7](#alg.replace-7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7343)

Let:

- [(7.1)](#alg.replace-7.1)

result_last be result + (last - first) for the overloads with no parameter result_last or result_r;

- [(7.2)](#alg.replace-7.2)

N be min(last - first, result_last - result)[.](#alg.replace-7.sentence-1)

[8](#alg.replace-8)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7353)

*Mandates*: The results of the expressions *first and new_value are writable ([[iterator.requirements.general]](iterator.requirements.general "24.3.1 General")) to result[.](#alg.replace-8.sentence-1)

[9](#alg.replace-9)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7358)

*Preconditions*: The ranges [first, last) and [result, result + N)
do not overlap[.](#alg.replace-9.sentence-1)

[10](#alg.replace-10)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7363)

*Effects*: Assigns through every iterator i in the range [result, result + N)
a new corresponding value

- [(10.1)](#alg.replace-10.1)

new_value if E(i) is true or

- [(10.2)](#alg.replace-10.2)

*(first + (i - result)) otherwise[.](#alg.replace-10.sentence-1)

[11](#alg.replace-11)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7373)

*Returns*: 

- [(11.1)](#alg.replace-11.1)

  result + N for the overloads in namespace std[.](#alg.replace-11.1.sentence-1)

- [(11.2)](#alg.replace-11.2)

  {first + N, result + N} for the overloads in namespace ranges[.](#alg.replace-11.2.sentence-1)

[12](#alg.replace-12)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7384)

*Complexity*: Exactly N applications
of the corresponding predicate and any projection[.](#alg.replace-12.sentence-1)

### [26.7.6](#alg.fill) Fill [[alg.fill]](alg.fill)

[🔗](#lib:fill)

`template<class ForwardIterator, class T = iterator_traits<ForwardIterator>::value_type>
  constexpr void fill(ForwardIterator first, ForwardIterator last, const T& value);
template<class ExecutionPolicy, class ForwardIterator,
         class T = iterator_traits<ForwardIterator>::value_type>
  void fill(ExecutionPolicy&& exec,
            ForwardIterator first, ForwardIterator last, const T& value);

template<class OutputIterator, class Size, class T = iterator_traits<OutputIterator>::value_type>
  constexpr OutputIterator fill_n(OutputIterator first, Size n, const T& value);
template<class ExecutionPolicy, class ForwardIterator, class Size,
         class T = iterator_traits<ForwardIterator>::value_type>
  ForwardIterator fill_n(ExecutionPolicy&& exec,
                         ForwardIterator first, Size n, const T& value);

template<class O, [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7 Concept sentinel_­for [iterator.concept.sentinel]")<O> S, class T = iter_value_t<O>>
  requires [output_iterator](iterator.concept.output#concept:output_iterator "24.3.4.10 Concept output_­iterator [iterator.concept.output]")<O, const T&>
  constexpr O ranges::fill(O first, S last, const T& value);
template<class R, class T = range_value_t<R>>
  requires [output_range](range.refinements#concept:output_range "25.4.6 Other range refinements [range.refinements]")<R, const T&>
  constexpr borrowed_iterator_t<R> ranges::fill(R&& r, const T& value);
template<class O, class T = iter_value_t<O>>
  requires [output_iterator](iterator.concept.output#concept:output_iterator "24.3.4.10 Concept output_­iterator [iterator.concept.output]")<O, const T&>
  constexpr O ranges::fill_n(O first, iter_difference_t<O> n, const T& value);

template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]") O, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<O> S,
         class T = iter_value_t<O>>
  requires [indirectly_writable](iterator.concept.writable#concept:indirectly_writable "24.3.4.3 Concept indirectly_­writable [iterator.concept.writable]")<O, const T&>
  O ranges::fill(Ep&& exec, O first, S last, const T& value);
template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6 Other range refinements [range.refinements]") R, class T = range_value_t<R>>
  requires [indirectly_writable](iterator.concept.writable#concept:indirectly_writable "24.3.4.3 Concept indirectly_­writable [iterator.concept.writable]")<iterator_t<R>, const T&>
  borrowed_iterator_t<R> fill(Ep&& exec, R&& r, const T& value);
template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]") O, class T = iter_value_t<O>>
  requires [indirectly_writable](iterator.concept.writable#concept:indirectly_writable "24.3.4.3 Concept indirectly_­writable [iterator.concept.writable]")<O, const T&>
  O ranges::fill_n(Ep&& exec, O first, iter_difference_t<O> n, const T& value);
`

[1](#alg.fill-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7432)

Let N be max(0, n) for the fill_n algorithms, andlast - first for the fill algorithms[.](#alg.fill-1.sentence-1)

[2](#alg.fill-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7436)

*Mandates*: The expression value is writable ([[iterator.requirements.general]](iterator.requirements.general "24.3.1 General")) to the output iterator[.](#alg.fill-2.sentence-1)

The type Size is convertible
to an integral type ([[conv.integral]](conv.integral "7.3.9 Integral conversions"), [[class.conv]](class.conv "11.4.8 Conversions"))[.](#alg.fill-2.sentence-2)

[3](#alg.fill-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7443)

*Effects*: Assigns value through all the iterators in the range [first, first + N)[.](#alg.fill-3.sentence-1)

[4](#alg.fill-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7448)

*Returns*: first + N[.](#alg.fill-4.sentence-1)

[5](#alg.fill-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7452)

*Complexity*: Exactly N assignments[.](#alg.fill-5.sentence-1)

### [26.7.7](#alg.generate) Generate [[alg.generate]](alg.generate)

[🔗](#lib:generate)

`template<class ForwardIterator, class Generator>
  constexpr void generate(ForwardIterator first, ForwardIterator last,
                          Generator gen);
template<class ExecutionPolicy, class ForwardIterator, class Generator>
  void generate(ExecutionPolicy&& exec,
                ForwardIterator first, ForwardIterator last,
                Generator gen);

template<class OutputIterator, class Size, class Generator>
  constexpr OutputIterator generate_n(OutputIterator first, Size n, Generator gen);
template<class ExecutionPolicy, class ForwardIterator, class Size, class Generator>
  ForwardIterator generate_n(ExecutionPolicy&& exec,
                             ForwardIterator first, Size n, Generator gen);

template<[input_or_output_iterator](iterator.concept.iterator#concept:input_or_output_iterator "24.3.4.6 Concept input_­or_­output_­iterator [iterator.concept.iterator]") O, [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7 Concept sentinel_­for [iterator.concept.sentinel]")<O> S, [copy_constructible](concept.copyconstructible#concept:copy_constructible "18.4.14 Concept copy_­constructible [concept.copyconstructible]") F>
  requires [invocable](concept.invocable#concept:invocable "18.7.2 Concept invocable [concept.invocable]")<F&> && [indirectly_writable](iterator.concept.writable#concept:indirectly_writable "24.3.4.3 Concept indirectly_­writable [iterator.concept.writable]")<O, invoke_result_t<F&>>
  constexpr O ranges::generate(O first, S last, F gen);
template<class R, [copy_constructible](concept.copyconstructible#concept:copy_constructible "18.4.14 Concept copy_­constructible [concept.copyconstructible]") F>
  requires [invocable](concept.invocable#concept:invocable "18.7.2 Concept invocable [concept.invocable]")<F&> && [output_range](range.refinements#concept:output_range "25.4.6 Other range refinements [range.refinements]")<R, invoke_result_t<F&>>
  constexpr borrowed_iterator_t<R> ranges::generate(R&& r, F gen);
template<[input_or_output_iterator](iterator.concept.iterator#concept:input_or_output_iterator "24.3.4.6 Concept input_­or_­output_­iterator [iterator.concept.iterator]") O, [copy_constructible](concept.copyconstructible#concept:copy_constructible "18.4.14 Concept copy_­constructible [concept.copyconstructible]") F>
  requires [invocable](concept.invocable#concept:invocable "18.7.2 Concept invocable [concept.invocable]")<F&> && [indirectly_writable](iterator.concept.writable#concept:indirectly_writable "24.3.4.3 Concept indirectly_­writable [iterator.concept.writable]")<O, invoke_result_t<F&>>
  constexpr O ranges::generate_n(O first, iter_difference_t<O> n, F gen);

template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]") O, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<O> S,
         [copy_constructible](concept.copyconstructible#concept:copy_constructible "18.4.14 Concept copy_­constructible [concept.copyconstructible]") F>
  requires [invocable](concept.invocable#concept:invocable "18.7.2 Concept invocable [concept.invocable]")<F&> && [indirectly_writable](iterator.concept.writable#concept:indirectly_writable "24.3.4.3 Concept indirectly_­writable [iterator.concept.writable]")<O, invoke_result_t<F&>>
  O ranges::generate(Ep&& exec, O first, S last, F gen);
template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6 Other range refinements [range.refinements]") R, [copy_constructible](concept.copyconstructible#concept:copy_constructible "18.4.14 Concept copy_­constructible [concept.copyconstructible]") F>
  requires [invocable](concept.invocable#concept:invocable "18.7.2 Concept invocable [concept.invocable]")<F&> && [indirectly_writable](iterator.concept.writable#concept:indirectly_writable "24.3.4.3 Concept indirectly_­writable [iterator.concept.writable]")<iterator_t<R>, invoke_result_t<F&>>
  borrowed_iterator_t<R> ranges::generate(Ep&& exec, R&& r, F gen);
template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]") O, [copy_constructible](concept.copyconstructible#concept:copy_constructible "18.4.14 Concept copy_­constructible [concept.copyconstructible]") F>
  requires [invocable](concept.invocable#concept:invocable "18.7.2 Concept invocable [concept.invocable]")<F&> && [indirectly_writable](iterator.concept.writable#concept:indirectly_writable "24.3.4.3 Concept indirectly_­writable [iterator.concept.writable]")<O, invoke_result_t<F&>>
  O ranges::generate_n(Ep&& exec, O first, iter_difference_t<O> n, F gen);
`

[1](#alg.generate-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7499)

Let N be max(0, n) for the generate_n algorithms, andlast - first for the generate algorithms[.](#alg.generate-1.sentence-1)

[2](#alg.generate-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7503)

*Mandates*: Size is convertible
to an integral type ([[conv.integral]](conv.integral "7.3.9 Integral conversions"), [[class.conv]](class.conv "11.4.8 Conversions"))[.](#alg.generate-2.sentence-1)

[3](#alg.generate-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7508)

*Effects*: Assigns the result of successive evaluations of gen() through each iterator in the range [first, first + N)[.](#alg.generate-3.sentence-1)

[4](#alg.generate-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7513)

*Returns*: first + N[.](#alg.generate-4.sentence-1)

[5](#alg.generate-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7517)

*Complexity*: Exactly N evaluations of gen() and assignments[.](#alg.generate-5.sentence-1)

[6](#alg.generate-6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7521)

*Remarks*: gen may modify objects via its arguments
for parallel algorithm overloads ([[algorithms.parallel.user]](algorithms.parallel.user "26.3.2 Requirements on user-provided function objects"))[.](#alg.generate-6.sentence-1)

### [26.7.8](#alg.remove) Remove [[alg.remove]](alg.remove)

[🔗](#lib:remove)

`template<class ForwardIterator, class T = iterator_traits<ForwardIterator>::value_type>
  constexpr ForwardIterator remove(ForwardIterator first, ForwardIterator last,
                                   const T& value);
template<class ExecutionPolicy, class ForwardIterator,
         class T = iterator_traits<ForwardIterator>::value_type>
  ForwardIterator remove(ExecutionPolicy&& exec,
                         ForwardIterator first, ForwardIterator last,
                         const T& value);

template<class ForwardIterator, class Predicate>
  constexpr ForwardIterator remove_if(ForwardIterator first, ForwardIterator last,
                                      Predicate pred);
template<class ExecutionPolicy, class ForwardIterator, class Predicate>
  ForwardIterator remove_if(ExecutionPolicy&& exec,
                            ForwardIterator first, ForwardIterator last,
                            Predicate pred);

template<[permutable](alg.req.permutable#concept:permutable "24.3.7.6 Concept permutable [alg.req.permutable]") I, [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7 Concept sentinel_­for [iterator.concept.sentinel]")<I> S, class Proj = identity,
         class T = projected_value_t<I, Proj>>
  requires [indirect_binary_predicate](indirectcallable.indirectinvocable#concept:indirect_binary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<ranges::equal_to, projected<I, Proj>, const T*>
  constexpr subrange<I> ranges::remove(I first, S last, const T& value, Proj proj = {});
template<[forward_range](range.refinements#concept:forward_range "25.4.6 Other range refinements [range.refinements]") R, class Proj = identity,
         class T = projected_value_t<iterator_t<R>, Proj>>
  requires [permutable](alg.req.permutable#concept:permutable "24.3.7.6 Concept permutable [alg.req.permutable]")<iterator_t<R>> &&
           [indirect_binary_predicate](indirectcallable.indirectinvocable#concept:indirect_binary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<ranges::equal_to, projected<iterator_t<R>, Proj>, const T*>
  constexpr borrowed_subrange_t<R>
    ranges::remove(R&& r, const T& value, Proj proj = {});

template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]") I, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<I> S,
         class Proj = identity, class T = projected_value_t<I, Proj>>
  requires [indirect_binary_predicate](indirectcallable.indirectinvocable#concept:indirect_binary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<ranges::equal_to, projected<I, Proj>, const T*>
  subrange<I>
    ranges::remove(Ep&& exec, I first, S last, const T& value, Proj proj = {});
template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6 Other range refinements [range.refinements]") R, class Proj = identity,
         class T = projected_value_t<iterator_t<R>, Proj>>
  requires [permutable](alg.req.permutable#concept:permutable "24.3.7.6 Concept permutable [alg.req.permutable]")<iterator_t<R>> &&
           [indirect_binary_predicate](indirectcallable.indirectinvocable#concept:indirect_binary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<ranges::equal_to,
                                      projected<iterator_t<R>, Proj>, const T*>
  borrowed_subrange_t<R>
    ranges::remove(Ep&& exec, R&& r, const T& value, Proj proj = {});

template<[permutable](alg.req.permutable#concept:permutable "24.3.7.6 Concept permutable [alg.req.permutable]") I, [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7 Concept sentinel_­for [iterator.concept.sentinel]")<I> S, class Proj = identity,
         [indirect_unary_predicate](indirectcallable.indirectinvocable#concept:indirect_unary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<projected<I, Proj>> Pred>
  constexpr subrange<I> ranges::remove_if(I first, S last, Pred pred, Proj proj = {});
template<[forward_range](range.refinements#concept:forward_range "25.4.6 Other range refinements [range.refinements]") R, class Proj = identity,
         [indirect_unary_predicate](indirectcallable.indirectinvocable#concept:indirect_unary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<projected<iterator_t<R>, Proj>> Pred>
  requires [permutable](alg.req.permutable#concept:permutable "24.3.7.6 Concept permutable [alg.req.permutable]")<iterator_t<R>>
  constexpr borrowed_subrange_t<R>
    ranges::remove_if(R&& r, Pred pred, Proj proj = {});

template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]") I, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<I> S,
         class Proj = identity, [indirect_unary_predicate](indirectcallable.indirectinvocable#concept:indirect_unary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<projected<I, Proj>> Pred>
  subrange<I>
    ranges::remove_if(Ep&& exec, I first, S last, Pred pred, Proj proj = {});
template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6 Other range refinements [range.refinements]") R, class Proj = identity,
         [indirect_unary_predicate](indirectcallable.indirectinvocable#concept:indirect_unary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<projected<iterator_t<R>, Proj>> Pred>
  requires [permutable](alg.req.permutable#concept:permutable "24.3.7.6 Concept permutable [alg.req.permutable]")<iterator_t<R>>
  borrowed_subrange_t<R>
    ranges::remove_if(Ep&& exec, R&& r, Pred pred, Proj proj = {});
`

[1](#alg.remove-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7594)

Let E be

- [(1.1)](#alg.remove-1.1)

bool(*i == value) for remove;

- [(1.2)](#alg.remove-1.2)

bool(pred(*i)) for remove_if;

- [(1.3)](#alg.remove-1.3)

bool(invoke(proj, *i) == value) for ranges​::​remove;

- [(1.4)](#alg.remove-1.4)

bool(invoke(pred, invoke(proj, *i))) for ranges​::​remove_if[.](#alg.remove-1.sentence-1)

[2](#alg.remove-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7603)

*Preconditions*: For the algorithms in namespace std,
the type of *first meets the [*Cpp17MoveAssignable*](utility.arg.requirements#:Cpp17MoveAssignable "16.4.4.2 Template argument requirements [utility.arg.requirements]") requirements (Table [33](utility.arg.requirements#tab:cpp17.moveassignable "Table 33: Cpp17MoveAssignable requirements"))[.](#alg.remove-2.sentence-1)

[3](#alg.remove-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7609)

*Effects*: Eliminates all the elements referred to by iterator i in the range [first, last) for which E holds[.](#alg.remove-3.sentence-1)

[4](#alg.remove-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7614)

*Returns*: Let j be the end of the resulting range[.](#alg.remove-4.sentence-1)

Returns:

- [(4.1)](#alg.remove-4.1)

  j for the overloads in namespace std[.](#alg.remove-4.1.sentence-1)

- [(4.2)](#alg.remove-4.2)

  {j, last} for the overloads in namespace ranges[.](#alg.remove-4.2.sentence-1)

[5](#alg.remove-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7622)

*Complexity*: Exactly last - first applications
of the corresponding predicate and any projection[.](#alg.remove-5.sentence-1)

[6](#alg.remove-6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7627)

*Remarks*: Stable ([[algorithm.stable]](algorithm.stable "16.4.6.8 Requirements for stable algorithms"))[.](#alg.remove-6.sentence-1)

[7](#alg.remove-7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7631)

[*Note [1](#alg.remove-note-1)*:

Each element in the range [ret, last),
where ret is the returned value,
has a valid but unspecified state,
because the algorithms can eliminate elements
by moving from elements that were originally in that range[.](#alg.remove-7.sentence-1)

— *end note*]

[🔗](#lib:remove_copy)

`template<class InputIterator, class OutputIterator,
         class T = iterator_traits<InputIterator>::value_type>
  constexpr OutputIterator
    remove_copy(InputIterator first, InputIterator last,
                OutputIterator result, const T& value);
template<class ExecutionPolicy, class ForwardIterator1, class ForwardIterator2,
         class T = iterator_traits<ForwardIterator1>::value_type>
  ForwardIterator2
    remove_copy(ExecutionPolicy&& exec,
                ForwardIterator1 first, ForwardIterator1 last,
                ForwardIterator2 result, const T& value);

template<class InputIterator, class OutputIterator, class Predicate>
  constexpr OutputIterator
    remove_copy_if(InputIterator first, InputIterator last,
                   OutputIterator result, Predicate pred);
template<class ExecutionPolicy, class ForwardIterator1, class ForwardIterator2,
         class Predicate>
  ForwardIterator2
    remove_copy_if(ExecutionPolicy&& exec,
                   ForwardIterator1 first, ForwardIterator1 last,
                   ForwardIterator2 result, Predicate pred);

template<[input_iterator](iterator.concept.input#concept:input_iterator "24.3.4.9 Concept input_­iterator [iterator.concept.input]") I, [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7 Concept sentinel_­for [iterator.concept.sentinel]")<I> S, [weakly_incrementable](iterator.concept.winc#concept:weakly_incrementable "24.3.4.4 Concept weakly_­incrementable [iterator.concept.winc]") O,
         class Proj = identity, class T = projected_value_t<I, Proj>>
  requires [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3 Concept indirectly_­copyable [alg.req.ind.copy]")<I, O> &&
           [indirect_binary_predicate](indirectcallable.indirectinvocable#concept:indirect_binary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<ranges::equal_to, projected<I, Proj>, const T*>
  constexpr ranges::remove_copy_result<I, O>
    ranges::remove_copy(I first, S last, O result, const T& value, Proj proj = {});
template<[input_range](range.refinements#concept:input_range "25.4.6 Other range refinements [range.refinements]") R, [weakly_incrementable](iterator.concept.winc#concept:weakly_incrementable "24.3.4.4 Concept weakly_­incrementable [iterator.concept.winc]") O, class Proj = identity,
         class T = projected_value_t<iterator_t<R>, Proj>>
  requires [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3 Concept indirectly_­copyable [alg.req.ind.copy]")<iterator_t<R>, O> &&
           [indirect_binary_predicate](indirectcallable.indirectinvocable#concept:indirect_binary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<ranges::equal_to, projected<iterator_t<R>, Proj>, const T*>
  constexpr ranges::remove_copy_result<borrowed_iterator_t<R>, O>
    ranges::remove_copy(R&& r, O result, const T& value, Proj proj = {});

template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]") I, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<I> S,
         [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]") O, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<O> OutS,
         class Proj = identity, class T = projected_value_t<I, Proj>>
  requires [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3 Concept indirectly_­copyable [alg.req.ind.copy]")<I, O> &&
           [indirect_binary_predicate](indirectcallable.indirectinvocable#concept:indirect_binary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<ranges::equal_to, projected<I, Proj>, const T*>
  ranges::remove_copy_result<I, O>
    ranges::remove_copy(Ep&& exec, I first, S last, O result, OutS result_last,
                        const T& value, Proj proj = {});
template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6 Other range refinements [range.refinements]") R, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6 Other range refinements [range.refinements]") OutR,
         class Proj = identity, class T = projected_value_t<iterator_t<R>, Proj>>
  requires [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3 Concept indirectly_­copyable [alg.req.ind.copy]")<iterator_t<R>, iterator_t<OutR>> &&
           [indirect_binary_predicate](indirectcallable.indirectinvocable#concept:indirect_binary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<ranges::equal_to,
                                      projected<iterator_t<R>, Proj>, const T*>
  ranges::remove_copy_result<borrowed_iterator_t<R>, borrowed_iterator_t<OutR>>
    ranges::remove_copy(Ep&& exec, R&& r, OutR&& result_r, const T& value, Proj proj = {});

template<[input_iterator](iterator.concept.input#concept:input_iterator "24.3.4.9 Concept input_­iterator [iterator.concept.input]") I, [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7 Concept sentinel_­for [iterator.concept.sentinel]")<I> S, [weakly_incrementable](iterator.concept.winc#concept:weakly_incrementable "24.3.4.4 Concept weakly_­incrementable [iterator.concept.winc]") O,
         class Proj = identity, [indirect_unary_predicate](indirectcallable.indirectinvocable#concept:indirect_unary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<projected<I, Proj>> Pred>
  requires [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3 Concept indirectly_­copyable [alg.req.ind.copy]")<I, O>
  constexpr ranges::remove_copy_if_result<I, O>
    ranges::remove_copy_if(I first, S last, O result, Pred pred, Proj proj = {});
template<[input_range](range.refinements#concept:input_range "25.4.6 Other range refinements [range.refinements]") R, [weakly_incrementable](iterator.concept.winc#concept:weakly_incrementable "24.3.4.4 Concept weakly_­incrementable [iterator.concept.winc]") O, class Proj = identity,
         [indirect_unary_predicate](indirectcallable.indirectinvocable#concept:indirect_unary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<projected<iterator_t<R>, Proj>> Pred>
  requires [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3 Concept indirectly_­copyable [alg.req.ind.copy]")<iterator_t<R>, O>
  constexpr ranges::remove_copy_if_result<borrowed_iterator_t<R>, O>
    ranges::remove_copy_if(R&& r, O result, Pred pred, Proj proj = {});

template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]") I, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<I> S,
         [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]") O, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<O> OutS,
         class Proj = identity, [indirect_unary_predicate](indirectcallable.indirectinvocable#concept:indirect_unary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<projected<I, Proj>> Pred>
  requires [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3 Concept indirectly_­copyable [alg.req.ind.copy]")<I, O>
  ranges::remove_copy_if_result<I, O>
    ranges::remove_copy_if(Ep&& exec, I first, S last, O result, OutS result_last,
                           Pred pred, Proj proj = {});
template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6 Other range refinements [range.refinements]") R, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6 Other range refinements [range.refinements]") OutR,
         class Proj = identity,
         [indirect_unary_predicate](indirectcallable.indirectinvocable#concept:indirect_unary_predicate "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<projected<iterator_t<R>, Proj>> Pred>
  requires [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3 Concept indirectly_­copyable [alg.req.ind.copy]")<iterator_t<R>, iterator_t<OutR>>
  ranges::remove_copy_if_result<borrowed_iterator_t<R>, borrowed_iterator_t<OutR>>
    ranges::remove_copy_if(Ep&& exec, R&& r, OutR&& result_r, Pred pred, Proj proj = {});
`

[8](#alg.remove-8)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7723)

Let E(i) be

- [(8.1)](#alg.remove-8.1)

bool(*i == value) for remove_copy;

- [(8.2)](#alg.remove-8.2)

bool(pred(*i)) for remove_copy_if;

- [(8.3)](#alg.remove-8.3)

bool(invoke(proj, *i) == value) for ranges​::​remove_copy;

- [(8.4)](#alg.remove-8.4)

bool(invoke(pred, invoke(proj, *i))) for ranges​::​remove_copy_if[.](#alg.remove-8.sentence-1)

[9](#alg.remove-9)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7732)

Let:

- [(9.1)](#alg.remove-9.1)

M be the number of iterators i in [first, last)
 for which E(i) is false;

- [(9.2)](#alg.remove-9.2)

result_last be result + M for the overloads with no parameter result_last or result_r;

- [(9.3)](#alg.remove-9.3)

N be min(M, result_last - result)[.](#alg.remove-9.sentence-1)

[10](#alg.remove-10)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7745)

*Mandates*: *first is writable ([[iterator.requirements.general]](iterator.requirements.general "24.3.1 General")) to result[.](#alg.remove-10.sentence-1)

[11](#alg.remove-11)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7749)

*Preconditions*: The ranges [first, last) and [result, result + N)
do not overlap[.](#alg.remove-11.sentence-1)

[*Note [2](#alg.remove-note-2)*:

For the parallel algorithm overloads in namespace std,
there can be a performance cost
if iterator_traits<ForwardIterator1>​::​value_type does not meet
the *Cpp17MoveConstructible* (Table [31](utility.arg.requirements#tab:cpp17.moveconstructible "Table 31: Cpp17MoveConstructible requirements")) requirements[.](#alg.remove-11.sentence-2)

For the parallel algorithm overloads in namespace ranges,
there can be a performance cost
if iter_value_t<I> does not model [move_constructible](concept.moveconstructible#concept:move_constructible "18.4.13 Concept move_­constructible [concept.moveconstructible]")[.](#alg.remove-11.sentence-3)

— *end note*]

[12](#alg.remove-12)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7763)

*Effects*: Copies the first N elements referred to by the iterator i in the range [first, last) for which E(i) is false into the range [result, result + N)[.](#alg.remove-12.sentence-1)

[13](#alg.remove-13)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7769)

*Returns*: 

- [(13.1)](#alg.remove-13.1)

  result + N,
 for the algorithms in namespace std[.](#alg.remove-13.1.sentence-1)

- [(13.2)](#alg.remove-13.2)

  {last, result + N},
 for the algorithms in namespace ranges,
 if N is equal to M[.](#alg.remove-13.2.sentence-1)

- [(13.3)](#alg.remove-13.3)

  Otherwise, {j, result_last},
 for the algorithms in namespace ranges,
 where j is the iterator in [first, last)
 for which E(j) is false and there are exactly N iterators i in [first, j)
 for which E(i) is false[.](#alg.remove-13.3.sentence-1)

[14](#alg.remove-14)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7788)

*Complexity*: At most last - first applications
of the corresponding predicate and any projection[.](#alg.remove-14.sentence-1)

[15](#alg.remove-15)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7793)

*Remarks*: Stable ([[algorithm.stable]](algorithm.stable "16.4.6.8 Requirements for stable algorithms"))[.](#alg.remove-15.sentence-1)

### [26.7.9](#alg.unique) Unique [[alg.unique]](alg.unique)

[🔗](#lib:unique)

`template<class ForwardIterator>
  constexpr ForwardIterator unique(ForwardIterator first, ForwardIterator last);
template<class ExecutionPolicy, class ForwardIterator>
  ForwardIterator unique(ExecutionPolicy&& exec,
                         ForwardIterator first, ForwardIterator last);

template<class ForwardIterator, class BinaryPredicate>
  constexpr ForwardIterator unique(ForwardIterator first, ForwardIterator last,
                                   BinaryPredicate pred);
template<class ExecutionPolicy, class ForwardIterator, class BinaryPredicate>
  ForwardIterator unique(ExecutionPolicy&& exec,
                         ForwardIterator first, ForwardIterator last,
                         BinaryPredicate pred);

template<[permutable](alg.req.permutable#concept:permutable "24.3.7.6 Concept permutable [alg.req.permutable]") I, [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7 Concept sentinel_­for [iterator.concept.sentinel]")<I> S, class Proj = identity,
         [indirect_equivalence_relation](indirectcallable.indirectinvocable#concept:indirect_equivalence_relation "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<projected<I, Proj>> C = ranges::equal_to>
  constexpr subrange<I> ranges::unique(I first, S last, C comp = {}, Proj proj = {});
template<[forward_range](range.refinements#concept:forward_range "25.4.6 Other range refinements [range.refinements]") R, class Proj = identity,
         [indirect_equivalence_relation](indirectcallable.indirectinvocable#concept:indirect_equivalence_relation "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<projected<iterator_t<R>, Proj>> C = ranges::equal_to>
  requires [permutable](alg.req.permutable#concept:permutable "24.3.7.6 Concept permutable [alg.req.permutable]")<iterator_t<R>>
  constexpr borrowed_subrange_t<R>
    ranges::unique(R&& r, C comp = {}, Proj proj = {});

template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]") I, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<I> S,
         class Proj = identity,
         [indirect_equivalence_relation](indirectcallable.indirectinvocable#concept:indirect_equivalence_relation "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<projected<I, Proj>> C = ranges::equal_to>
  requires [permutable](alg.req.permutable#concept:permutable "24.3.7.6 Concept permutable [alg.req.permutable]")<I>
  subrange<I> ranges::unique(Ep&& exec, I first, S last, C comp = {}, Proj proj = {});
template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6 Other range refinements [range.refinements]") R, class Proj = identity,
         [indirect_equivalence_relation](indirectcallable.indirectinvocable#concept:indirect_equivalence_relation "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<projected<iterator_t<R>, Proj>> C = ranges::equal_to>
  requires [permutable](alg.req.permutable#concept:permutable "24.3.7.6 Concept permutable [alg.req.permutable]")<iterator_t<R>>
  borrowed_subrange_t<R> ranges::unique(Ep&& exec, R&& r, C comp = {}, Proj proj = {});
`

[1](#alg.unique-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7837)

Let pred be equal_to{} for the overloads with no parameter pred, and
let E be

- [(1.1)](#alg.unique-1.1)

bool(pred(*(i - 1), *i)) for the overloads in namespace std;

- [(1.2)](#alg.unique-1.2)

bool(invoke(comp, invoke(proj, *(i - 1)), invoke(proj, *i))) for the overloads in namespace ranges[.](#alg.unique-1.sentence-1)

[2](#alg.unique-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7851)

*Preconditions*: For the overloads in namespace std,pred is an equivalence relation and
the type of *first meets
the [*Cpp17MoveAssignable*](utility.arg.requirements#:Cpp17MoveAssignable "16.4.4.2 Template argument requirements [utility.arg.requirements]") requirements (Table [33](utility.arg.requirements#tab:cpp17.moveassignable "Table 33: Cpp17MoveAssignable requirements"))[.](#alg.unique-2.sentence-1)

[3](#alg.unique-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7858)

*Effects*: For a nonempty range, eliminates all but the first element
from every consecutive group of equivalent elements referred to
by the iterator i in the range [first + 1, last)
for which E is true[.](#alg.unique-3.sentence-1)

[4](#alg.unique-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7865)

*Returns*: Let j be the end of the resulting range[.](#alg.unique-4.sentence-1)

Returns:

- [(4.1)](#alg.unique-4.1)

  j for the overloads in namespace std[.](#alg.unique-4.1.sentence-1)

- [(4.2)](#alg.unique-4.2)

  {j, last} for the overloads in namespace ranges[.](#alg.unique-4.2.sentence-1)

[5](#alg.unique-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7873)

*Complexity*: For nonempty ranges, exactly (last - first) - 1 applications
of the corresponding predicate and
no more than twice as many applications of any projection[.](#alg.unique-5.sentence-1)

[🔗](#lib:unique_copy)

`template<class InputIterator, class OutputIterator>
  constexpr OutputIterator
    unique_copy(InputIterator first, InputIterator last,
                OutputIterator result);
template<class ExecutionPolicy, class ForwardIterator1, class ForwardIterator2>
  ForwardIterator2
    unique_copy(ExecutionPolicy&& exec,
                ForwardIterator1 first, ForwardIterator1 last,
                ForwardIterator2 result);

template<class InputIterator, class OutputIterator,
         class BinaryPredicate>
  constexpr OutputIterator
    unique_copy(InputIterator first, InputIterator last,
                OutputIterator result, BinaryPredicate pred);
template<class ExecutionPolicy, class ForwardIterator1, class ForwardIterator2,
         class BinaryPredicate>
  ForwardIterator2
    unique_copy(ExecutionPolicy&& exec,
                ForwardIterator1 first, ForwardIterator1 last,
                ForwardIterator2 result, BinaryPredicate pred);

template<[input_iterator](iterator.concept.input#concept:input_iterator "24.3.4.9 Concept input_­iterator [iterator.concept.input]") I, [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7 Concept sentinel_­for [iterator.concept.sentinel]")<I> S, [weakly_incrementable](iterator.concept.winc#concept:weakly_incrementable "24.3.4.4 Concept weakly_­incrementable [iterator.concept.winc]") O, class Proj = identity,
         [indirect_equivalence_relation](indirectcallable.indirectinvocable#concept:indirect_equivalence_relation "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<projected<I, Proj>> C = ranges::equal_to>
  requires [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3 Concept indirectly_­copyable [alg.req.ind.copy]")<I, O> &&
           ([forward_iterator](iterator.concept.forward#concept:forward_iterator "24.3.4.11 Concept forward_­iterator [iterator.concept.forward]")<I> ||
            ([input_iterator](iterator.concept.input#concept:input_iterator "24.3.4.9 Concept input_­iterator [iterator.concept.input]")<O> && [same_as](concept.same#concept:same_as "18.4.2 Concept same_­as [concept.same]")<iter_value_t<I>, iter_value_t<O>>) ||
            [indirectly_copyable_storable](alg.req.ind.copy#concept:indirectly_copyable_storable "24.3.7.3 Concept indirectly_­copyable [alg.req.ind.copy]")<I, O>)
  constexpr ranges::unique_copy_result<I, O>
    ranges::unique_copy(I first, S last, O result, C comp = {}, Proj proj = {});
template<[input_range](range.refinements#concept:input_range "25.4.6 Other range refinements [range.refinements]") R, [weakly_incrementable](iterator.concept.winc#concept:weakly_incrementable "24.3.4.4 Concept weakly_­incrementable [iterator.concept.winc]") O, class Proj = identity,
         [indirect_equivalence_relation](indirectcallable.indirectinvocable#concept:indirect_equivalence_relation "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<projected<iterator_t<R>, Proj>> C = ranges::equal_to>
  requires [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3 Concept indirectly_­copyable [alg.req.ind.copy]")<iterator_t<R>, O> &&
           ([forward_iterator](iterator.concept.forward#concept:forward_iterator "24.3.4.11 Concept forward_­iterator [iterator.concept.forward]")<iterator_t<R>> ||
            ([input_iterator](iterator.concept.input#concept:input_iterator "24.3.4.9 Concept input_­iterator [iterator.concept.input]")<O> && [same_as](concept.same#concept:same_as "18.4.2 Concept same_­as [concept.same]")<range_value_t<R>, iter_value_t<O>>) ||
            [indirectly_copyable_storable](alg.req.ind.copy#concept:indirectly_copyable_storable "24.3.7.3 Concept indirectly_­copyable [alg.req.ind.copy]")<iterator_t<R>, O>)
  constexpr ranges::unique_copy_result<borrowed_iterator_t<R>, O>
    ranges::unique_copy(R&& r, O result, C comp = {}, Proj proj = {});

template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]") I, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<I> S,
         [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]") O, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<O> OutS, class Proj = identity,
         [indirect_equivalence_relation](indirectcallable.indirectinvocable#concept:indirect_equivalence_relation "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<projected<I, Proj>> C = ranges::equal_to>
  requires [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3 Concept indirectly_­copyable [alg.req.ind.copy]")<I, O>
  ranges::unique_copy_result<I, O>
    ranges::unique_copy(Ep&& exec, I first, S last, O result, OutS result_last,
                        C comp = {}, Proj proj = {});
template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6 Other range refinements [range.refinements]") R, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6 Other range refinements [range.refinements]") OutR,
         class Proj = identity,
         [indirect_equivalence_relation](indirectcallable.indirectinvocable#concept:indirect_equivalence_relation "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<projected<iterator_t<R>, Proj>> C = ranges::equal_to>
  requires [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3 Concept indirectly_­copyable [alg.req.ind.copy]")<iterator_t<R>, iterator_t<OutR>>
  ranges::unique_copy_result<borrowed_iterator_t<R>, borrowed_iterator_t<OutR>>
    ranges::unique_copy(Ep&& exec, R&& r, OutR&& result_r, C comp = {}, Proj proj = {});
`

[6](#alg.unique-6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7937)

Let pred be equal_to{} for the overloads
in namespace std with no parameter pred, and
let E(i) be

- [(6.1)](#alg.unique-6.1)

bool(pred(*i, *(i - 1))) for the overloads in namespace std;

- [(6.2)](#alg.unique-6.2)

bool(invoke(comp, invoke(proj, *i), invoke(proj, *(i - 1)))) for the overloads in namespace ranges[.](#alg.unique-6.sentence-1)

[7](#alg.unique-7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7951)

Let:

- [(7.1)](#alg.unique-7.1)

M be the number of iterators i in the range [first + 1, last)
 for which E(i) is false;

- [(7.2)](#alg.unique-7.2)

result_last be result + M + 1 for the overloads with no parameter result_last or result_r;

- [(7.3)](#alg.unique-7.3)

N be min(M+1, result_last - result)[.](#alg.unique-7.sentence-1)

[8](#alg.unique-8)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7964)

*Mandates*: *first is writable ([[iterator.requirements.general]](iterator.requirements.general "24.3.1 General")) to result[.](#alg.unique-8.sentence-1)

[9](#alg.unique-9)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L7968)

*Preconditions*: 

- [(9.1)](#alg.unique-9.1)

  The ranges [first, last) and [result, result + N)
 do not overlap[.](#alg.unique-9.1.sentence-1)

- [(9.2)](#alg.unique-9.2)

  For the overloads in namespace std:
  * [(9.2.1)](#alg.unique-9.2.1)

      The comparison function is an equivalence relation[.](#alg.unique-9.2.1.sentence-1)

  * [(9.2.2)](#alg.unique-9.2.2)

      For the overloads with no ExecutionPolicy,
 let T be the value type of InputIterator[.](#alg.unique-9.2.2.sentence-1)
      If InputIterator models [forward_iterator](iterator.concept.forward#concept:forward_iterator "24.3.4.11 Concept forward_­iterator [iterator.concept.forward]") ([[iterator.concept.forward]](iterator.concept.forward "24.3.4.11 Concept forward_­iterator")),
 then there are no additional requirements for T[.](#alg.unique-9.2.2.sentence-2)
      Otherwise, if OutputIterator meets
 the [*Cpp17ForwardIterator*](forward.iterators#:Cpp17ForwardIterator "24.3.5.5 Forward iterators [forward.iterators]") requirements and
 its value type is the same as T,
 then T meets
 the [*Cpp17CopyAssignable*](utility.arg.requirements#:Cpp17CopyAssignable "16.4.4.2 Template argument requirements [utility.arg.requirements]") (Table [34](utility.arg.requirements#tab:cpp17.copyassignable "Table 34: Cpp17CopyAssignable requirements (in addition to Cpp17MoveAssignable)")) requirements[.](#alg.unique-9.2.2.sentence-3)
      Otherwise, T meets both
 the *Cpp17CopyConstructible* (Table [32](utility.arg.requirements#tab:cpp17.copyconstructible "Table 32: Cpp17CopyConstructible requirements (in addition to Cpp17MoveConstructible)")) and *Cpp17CopyAssignable* requirements[.](#alg.unique-9.2.2.sentence-4)

[*Note [1](#alg.unique-note-1)*:

For the parallel algorithm overloads in namespace std,
there can be a performance cost
if the value type of ForwardIterator1 does not meet both the*Cpp17CopyConstructible* and *Cpp17CopyAssignable* requirements[.](#alg.unique-9.sentence-2)

For the parallel algorithm overloads in namespace ranges,
there can be a performance cost if iter_value_t<I> does not model [copyable](concepts.object#concept:copyable "18.6 Object concepts [concepts.object]")[.](#alg.unique-9.sentence-3)

— *end note*]

[10](#alg.unique-10)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8005)

*Effects*: Copies only the first element from N consecutive groups of equivalent elements
referred to by the iterator i in the range [first + 1, last)
for which E(i) holds
into the range [result, result + N)[.](#alg.unique-10.sentence-1)

[11](#alg.unique-11)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8012)

*Returns*: 

- [(11.1)](#alg.unique-11.1)

  result + N for the overloads in namespace std[.](#alg.unique-11.1.sentence-1)

- [(11.2)](#alg.unique-11.2)

  {last, result + N} for the overloads in namespace ranges,
 if N is equal to M+1[.](#alg.unique-11.2.sentence-1)

- [(11.3)](#alg.unique-11.3)

  Otherwise, {j, result_last} for the overloads in namespace ranges,
 where j is the iterator in [first + 1, last)
 for which E(j) is false and there are exactly N−1 iterators i in [first + 1, j)
 for which E(i) is false[.](#alg.unique-11.3.sentence-1)

[12](#alg.unique-12)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8031)

*Complexity*: At most last - first - 1 applications
of the corresponding predicate
and no more than twice as many applications of any projection[.](#alg.unique-12.sentence-1)

### [26.7.10](#alg.reverse) Reverse [[alg.reverse]](alg.reverse)

[🔗](#lib:reverse)

`template<class BidirectionalIterator>
  constexpr void reverse(BidirectionalIterator first, BidirectionalIterator last);
template<class ExecutionPolicy, class BidirectionalIterator>
  void reverse(ExecutionPolicy&& exec,
               BidirectionalIterator first, BidirectionalIterator last);

template<[bidirectional_iterator](iterator.concept.bidir#concept:bidirectional_iterator "24.3.4.12 Concept bidirectional_­iterator [iterator.concept.bidir]") I, [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7 Concept sentinel_­for [iterator.concept.sentinel]")<I> S>
  requires [permutable](alg.req.permutable#concept:permutable "24.3.7.6 Concept permutable [alg.req.permutable]")<I>
  constexpr I ranges::reverse(I first, S last);
template<[bidirectional_range](range.refinements#concept:bidirectional_range "25.4.6 Other range refinements [range.refinements]") R>
  requires [permutable](alg.req.permutable#concept:permutable "24.3.7.6 Concept permutable [alg.req.permutable]")<iterator_t<R>>
  constexpr borrowed_iterator_t<R> ranges::reverse(R&& r);

template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]") I, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<I> S>
  requires [permutable](alg.req.permutable#concept:permutable "24.3.7.6 Concept permutable [alg.req.permutable]")<I>
  I ranges::reverse(Ep&& exec, I first, S last);
template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6 Other range refinements [range.refinements]") R>
  requires [permutable](alg.req.permutable#concept:permutable "24.3.7.6 Concept permutable [alg.req.permutable]")<iterator_t<R>>
  borrowed_iterator_t<R> ranges::reverse(Ep&& exec, R&& r);
`

[1](#alg.reverse-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8064)

*Preconditions*: For the overloads in namespace std,BidirectionalIterator meets
the [*Cpp17ValueSwappable*](swappable.requirements#:Cpp17ValueSwappable "16.4.4.3 Swappable requirements [swappable.requirements]") requirements ([[swappable.requirements]](swappable.requirements "16.4.4.3 Swappable requirements"))[.](#alg.reverse-1.sentence-1)

[2](#alg.reverse-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8070)

*Effects*: For each non-negative integer i < (last - first) / 2,
applies std​::​iter_swap, orranges​::​​iter_swap for the overloads in namespace ranges,
to all pairs of iterators first + i, (last - i) - 1[.](#alg.reverse-2.sentence-1)

[3](#alg.reverse-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8077)

*Returns*: last for the overloads in namespace ranges[.](#alg.reverse-3.sentence-1)

[4](#alg.reverse-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8081)

*Complexity*: Exactly (last - first)/2 swaps[.](#alg.reverse-4.sentence-1)

[🔗](#lib:reverse_copy)

`template<class BidirectionalIterator, class OutputIterator>
  constexpr OutputIterator
    reverse_copy(BidirectionalIterator first, BidirectionalIterator last,
                 OutputIterator result);
template<class ExecutionPolicy, class BidirectionalIterator, class ForwardIterator>
  ForwardIterator
    reverse_copy(ExecutionPolicy&& exec,
                 BidirectionalIterator first, BidirectionalIterator last,
                 ForwardIterator result);

template<[bidirectional_iterator](iterator.concept.bidir#concept:bidirectional_iterator "24.3.4.12 Concept bidirectional_­iterator [iterator.concept.bidir]") I, [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7 Concept sentinel_­for [iterator.concept.sentinel]")<I> S, [weakly_incrementable](iterator.concept.winc#concept:weakly_incrementable "24.3.4.4 Concept weakly_­incrementable [iterator.concept.winc]") O>
  requires [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3 Concept indirectly_­copyable [alg.req.ind.copy]")<I, O>
  constexpr ranges::reverse_copy_result<I, O>
    ranges::reverse_copy(I first, S last, O result);
template<[bidirectional_range](range.refinements#concept:bidirectional_range "25.4.6 Other range refinements [range.refinements]") R, [weakly_incrementable](iterator.concept.winc#concept:weakly_incrementable "24.3.4.4 Concept weakly_­incrementable [iterator.concept.winc]") O>
  requires [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3 Concept indirectly_­copyable [alg.req.ind.copy]")<iterator_t<R>, O>
  constexpr ranges::reverse_copy_result<borrowed_iterator_t<R>, O>
    ranges::reverse_copy(R&& r, O result);
`

[5](#alg.reverse-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8109)

Let N be last - first[.](#alg.reverse-5.sentence-1)

[6](#alg.reverse-6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8112)

*Preconditions*: The ranges [first, last) and [result, result + N)
do not overlap[.](#alg.reverse-6.sentence-1)

[7](#alg.reverse-7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8117)

*Effects*: Copies the range [first, last) to the range [result, result + N)
such that for every non-negative integer i < N the following assignment takes place:*(result + N - 1 - i) = *(first + i)[.](#alg.reverse-7.sentence-1)

[8](#alg.reverse-8)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8124)

*Returns*: 

- [(8.1)](#alg.reverse-8.1)

  result + N for the overloads in namespace std[.](#alg.reverse-8.1.sentence-1)

- [(8.2)](#alg.reverse-8.2)

  {last, result + N} for the overloads in namespace ranges[.](#alg.reverse-8.2.sentence-1)

[9](#alg.reverse-9)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8133)

*Complexity*: Exactly N assignments[.](#alg.reverse-9.sentence-1)

[🔗](#alg.reverse-itemdecl:3)

`template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]") I, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<I> S,
         [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]") O, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<O> OutS>
  requires [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3 Concept indirectly_­copyable [alg.req.ind.copy]")<I, O>
  ranges::reverse_copy_truncated_result<I, O>
    ranges::reverse_copy(Ep&& exec, I first, S last, O result,
                         OutS result_last);
template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6 Other range refinements [range.refinements]") R, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6 Other range refinements [range.refinements]") OutR>
  requires [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3 Concept indirectly_­copyable [alg.req.ind.copy]")<iterator_t<R>, iterator_t<OutR>>
  ranges::reverse_copy_truncated_result<borrowed_iterator_t<R>, borrowed_iterator_t<OutR>>
    ranges::reverse_copy(Ep&& exec, R&& r, OutR&& result_r);
`

[10](#alg.reverse-10)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8152)

Let N be min(last - first, result_last - result),
and let *NEW_FIRST* be first + (last - first) - N[.](#alg.reverse-10.sentence-1)

[11](#alg.reverse-11)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8156)

*Preconditions*: The ranges [first, last) and [result, result + N)
do not overlap[.](#alg.reverse-11.sentence-1)

[12](#alg.reverse-12)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8161)

*Effects*: Copies the range [*NEW_FIRST*, last)
to the range [result, result + N)
such that for every non-negative integer i<N the following assignment takes place:*(result + N - 1 - i) = *(*NEW_FIRST* + i)[.](#alg.reverse-12.sentence-1)

[13](#alg.reverse-13)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8169)

*Returns*: {last, *NEW_FIRST*, result + N}[.](#alg.reverse-13.sentence-1)

[14](#alg.reverse-14)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8173)

*Complexity*: Exactly N assignments[.](#alg.reverse-14.sentence-1)

### [26.7.11](#alg.rotate) Rotate [[alg.rotate]](alg.rotate)

[🔗](#lib:rotate)

`template<class ForwardIterator>
  constexpr ForwardIterator
    rotate(ForwardIterator first, ForwardIterator middle, ForwardIterator last);
template<class ExecutionPolicy, class ForwardIterator>
  ForwardIterator
    rotate(ExecutionPolicy&& exec,
           ForwardIterator first, ForwardIterator middle, ForwardIterator last);

template<[permutable](alg.req.permutable#concept:permutable "24.3.7.6 Concept permutable [alg.req.permutable]") I, [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7 Concept sentinel_­for [iterator.concept.sentinel]")<I> S>
  constexpr subrange<I> ranges::rotate(I first, I middle, S last);
template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]") I, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<I> S>
  requires [permutable](alg.req.permutable#concept:permutable "24.3.7.6 Concept permutable [alg.req.permutable]")<I>
  subrange<I> ranges::rotate(Ep&& exec, I first, I middle, S last);
`

[1](#alg.rotate-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8198)

*Preconditions*: [first, middle) and [middle, last) are valid ranges[.](#alg.rotate-1.sentence-1)

For the overloads in namespace std,ForwardIterator meets
the [*Cpp17ValueSwappable*](swappable.requirements#:Cpp17ValueSwappable "16.4.4.3 Swappable requirements [swappable.requirements]") requirements ([[swappable.requirements]](swappable.requirements "16.4.4.3 Swappable requirements")), and
the type of *first meets
the [*Cpp17MoveConstructible*](utility.arg.requirements#:Cpp17MoveConstructible "16.4.4.2 Template argument requirements [utility.arg.requirements]") (Table [31](utility.arg.requirements#tab:cpp17.moveconstructible "Table 31: Cpp17MoveConstructible requirements")) and[*Cpp17MoveAssignable*](utility.arg.requirements#:Cpp17MoveAssignable "16.4.4.2 Template argument requirements [utility.arg.requirements]") (Table [33](utility.arg.requirements#tab:cpp17.moveassignable "Table 33: Cpp17MoveAssignable requirements")) requirements[.](#alg.rotate-1.sentence-2)

[2](#alg.rotate-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8208)

*Effects*: For each non-negative integer i < (last - first),
places the element from the position first + i into position first + (i + (last - middle)) % (last - first)[.](#alg.rotate-2.sentence-1)

[*Note [1](#alg.rotate-note-1)*:

This is a left rotate[.](#alg.rotate-2.sentence-2)

— *end note*]

[3](#alg.rotate-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8217)

*Returns*: 

- [(3.1)](#alg.rotate-3.1)

  first + (last - middle) for the overloads in namespace std[.](#alg.rotate-3.1.sentence-1)

- [(3.2)](#alg.rotate-3.2)

  {first + (last - middle), last} for the overload in namespace ranges[.](#alg.rotate-3.2.sentence-1)

[4](#alg.rotate-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8228)

*Complexity*: At most last - first swaps[.](#alg.rotate-4.sentence-1)

[🔗](#alg.rotate-itemdecl:2)

`template<[forward_range](range.refinements#concept:forward_range "25.4.6 Other range refinements [range.refinements]") R>
  requires [permutable](alg.req.permutable#concept:permutable "24.3.7.6 Concept permutable [alg.req.permutable]")<iterator_t<R>>
  constexpr borrowed_subrange_t<R> ranges::rotate(R&& r, iterator_t<R> middle);
`

[5](#alg.rotate-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8240)

*Effects*: Equivalent to:return ranges​::​rotate(ranges​::​begin(r), middle, ranges​::​end(r));

[🔗](#alg.rotate-itemdecl:3)

`template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6 Other range refinements [range.refinements]") R>
  requires [permutable](alg.req.permutable#concept:permutable "24.3.7.6 Concept permutable [alg.req.permutable]")<iterator_t<R>>
  borrowed_subrange_t<R> ranges::rotate(Ep&& exec, R&& r, iterator_t<R> middle);
`

[6](#alg.rotate-6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8253)

*Effects*: Equivalent to:return ranges::rotate(std::forward<Ep>(exec), ranges::begin(r), middle, ranges::end(r));

[🔗](#lib:rotate_copy)

`template<class ForwardIterator, class OutputIterator>
  constexpr OutputIterator
    rotate_copy(ForwardIterator first, ForwardIterator middle, ForwardIterator last,
                OutputIterator result);
template<class ExecutionPolicy, class ForwardIterator1, class ForwardIterator2>
  ForwardIterator2
    rotate_copy(ExecutionPolicy&& exec,
                ForwardIterator1 first, ForwardIterator1 middle, ForwardIterator1 last,
                ForwardIterator2 result);

  template<[forward_iterator](iterator.concept.forward#concept:forward_iterator "24.3.4.11 Concept forward_­iterator [iterator.concept.forward]") I, [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7 Concept sentinel_­for [iterator.concept.sentinel]")<I> S, [weakly_incrementable](iterator.concept.winc#concept:weakly_incrementable "24.3.4.4 Concept weakly_­incrementable [iterator.concept.winc]") O>
    requires [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3 Concept indirectly_­copyable [alg.req.ind.copy]")<I, O>
    constexpr ranges::rotate_copy_result<I, O>
      ranges::rotate_copy(I first, I middle, S last, O result);
`

[7](#alg.rotate-7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8280)

Let N be last - first[.](#alg.rotate-7.sentence-1)

[8](#alg.rotate-8)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8283)

*Preconditions*: [first, middle) and [middle, last) are valid ranges[.](#alg.rotate-8.sentence-1)

The ranges [first, last) and [result, result + N)
do not overlap[.](#alg.rotate-8.sentence-2)

[9](#alg.rotate-9)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8289)

*Effects*: Copies the range [first, last) to the range [result, result + N)
such that for each non-negative integer i<N the following assignment takes place:*(result + i) = *(first + (i + (middle - first)) % N)[.](#alg.rotate-9.sentence-1)

[10](#alg.rotate-10)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8296)

*Returns*: 

- [(10.1)](#alg.rotate-10.1)

  result + N for the overloads in namespace std[.](#alg.rotate-10.1.sentence-1)

- [(10.2)](#alg.rotate-10.2)

  {last, result + N} for the overload in namespace ranges[.](#alg.rotate-10.2.sentence-1)

[11](#alg.rotate-11)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8305)

*Complexity*: Exactly N assignments[.](#alg.rotate-11.sentence-1)

[🔗](#alg.rotate-itemdecl:5)

`template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]") I, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<I> S,
         [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]") O, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<O> OutS>
  requires [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3 Concept indirectly_­copyable [alg.req.ind.copy]")<I, O>
  ranges::rotate_copy_truncated_result<I, O>
    ranges::rotate_copy(Ep&& exec, I first, I middle, S last, O result, OutS result_last);
`

[12](#alg.rotate-12)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8319)

Let M be last - first and N be min(M, result_last - result)[.](#alg.rotate-12.sentence-1)

[13](#alg.rotate-13)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8323)

*Preconditions*: [first, middle) and [middle, last)
are valid ranges[.](#alg.rotate-13.sentence-1)

The ranges [first, last) and [result, result + N)
do not overlap[.](#alg.rotate-13.sentence-2)

[14](#alg.rotate-14)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8330)

*Effects*: Copies the range [first, last)
to the range [result, result + N)
such that for each non-negative integer i<N the following assignment takes place:*(result + i) = *(first + (i + (middle - first)) % M)[.](#alg.rotate-14.sentence-1)

[15](#alg.rotate-15)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8338)

*Returns*: 

- [(15.1)](#alg.rotate-15.1)

  {middle + N, first, result + N} if N is less than last - middle[.](#alg.rotate-15.1.sentence-1)

- [(15.2)](#alg.rotate-15.2)

  Otherwise, {last, first + (N + (middle - first)) % M, result + N}[.](#alg.rotate-15.2.sentence-1)

[16](#alg.rotate-16)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8349)

*Complexity*: Exactly N assignments[.](#alg.rotate-16.sentence-1)

[🔗](#alg.rotate-itemdecl:6)

`template<[forward_range](range.refinements#concept:forward_range "25.4.6 Other range refinements [range.refinements]") R, [weakly_incrementable](iterator.concept.winc#concept:weakly_incrementable "24.3.4.4 Concept weakly_­incrementable [iterator.concept.winc]") O>
  requires [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3 Concept indirectly_­copyable [alg.req.ind.copy]")<iterator_t<R>, O>
  constexpr ranges::rotate_copy_result<borrowed_iterator_t<R>, O>
    ranges::rotate_copy(R&& r, iterator_t<R> middle, O result);
`

[17](#alg.rotate-17)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8362)

*Effects*: Equivalent to:return ranges::rotate_copy(ranges::begin(r), middle, ranges::end(r), std::move(result));

[🔗](#alg.rotate-itemdecl:7)

`template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6 Other range refinements [range.refinements]") R, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6 Other range refinements [range.refinements]") OutR>
  requires [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3 Concept indirectly_­copyable [alg.req.ind.copy]")<iterator_t<R>, iterator_t<OutR>>
  ranges::rotate_copy_truncated_result<borrowed_iterator_t<R>, borrowed_iterator_t<OutR>>
    ranges::rotate_copy(Ep&& exec, R&& r, iterator_t<R> middle, OutR&& result_r);
`

[18](#alg.rotate-18)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8378)

*Effects*: Equivalent to:return ranges::rotate_copy(std::forward<Ep>(exec), ranges::begin(r), middle, ranges::end(r),
 ranges::begin(result_r), ranges::end(result_r));

### [26.7.12](#alg.random.sample) Sample [[alg.random.sample]](alg.random.sample)

[🔗](#lib:sample)

`template<class PopulationIterator, class SampleIterator,
         class Distance, class UniformRandomBitGenerator>
  SampleIterator sample(PopulationIterator first, PopulationIterator last,
                        SampleIterator out, Distance n,
                        UniformRandomBitGenerator&& g);

template<[input_iterator](iterator.concept.input#concept:input_iterator "24.3.4.9 Concept input_­iterator [iterator.concept.input]") I, [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7 Concept sentinel_­for [iterator.concept.sentinel]")<I> S, [weakly_incrementable](iterator.concept.winc#concept:weakly_incrementable "24.3.4.4 Concept weakly_­incrementable [iterator.concept.winc]") O, class Gen>
  requires ([forward_iterator](iterator.concept.forward#concept:forward_iterator "24.3.4.11 Concept forward_­iterator [iterator.concept.forward]")<I> || [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]")<O>) &&
           [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3 Concept indirectly_­copyable [alg.req.ind.copy]")<I, O> &&
           [uniform_random_bit_generator](rand.req.urng#concept:uniform_random_bit_generator "29.5.3.3 Uniform random bit generator requirements [rand.req.urng]")<remove_reference_t<Gen>>
  O ranges::sample(I first, S last, O out, iter_difference_t<I> n, Gen&& g);
template<[input_range](range.refinements#concept:input_range "25.4.6 Other range refinements [range.refinements]") R, [weakly_incrementable](iterator.concept.winc#concept:weakly_incrementable "24.3.4.4 Concept weakly_­incrementable [iterator.concept.winc]") O, class Gen>
  requires ([forward_range](range.refinements#concept:forward_range "25.4.6 Other range refinements [range.refinements]")<R> || [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]")<O>) &&
           [indirectly_copyable](alg.req.ind.copy#concept:indirectly_copyable "24.3.7.3 Concept indirectly_­copyable [alg.req.ind.copy]")<iterator_t<R>, O> &&
           [uniform_random_bit_generator](rand.req.urng#concept:uniform_random_bit_generator "29.5.3.3 Uniform random bit generator requirements [rand.req.urng]")<remove_reference_t<Gen>>
  O ranges::sample(R&& r, O out, range_difference_t<R> n, Gen&& g);
`

[1](#alg.random.sample-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8410)

*Mandates*: For the overload in namespace std,Distance is an integer type and*first is writable ([[iterator.requirements.general]](iterator.requirements.general "24.3.1 General")) to out[.](#alg.random.sample-1.sentence-1)

[2](#alg.random.sample-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8416)

*Preconditions*: out is not in the range [first, last)[.](#alg.random.sample-2.sentence-1)

For the overload in namespace std:

- [(2.1)](#alg.random.sample-2.1)

  PopulationIterator meets
 the [*Cpp17InputIterator*](input.iterators#:Cpp17InputIterator "24.3.5.3 Input iterators [input.iterators]") requirements ([[input.iterators]](input.iterators "24.3.5.3 Input iterators"))[.](#alg.random.sample-2.1.sentence-1)

- [(2.2)](#alg.random.sample-2.2)

  SampleIterator meets
 the [*Cpp17OutputIterator*](output.iterators#:Cpp17OutputIterator "24.3.5.4 Output iterators [output.iterators]") requirements ([[output.iterators]](output.iterators "24.3.5.4 Output iterators"))[.](#alg.random.sample-2.2.sentence-1)

- [(2.3)](#alg.random.sample-2.3)

  SampleIterator meets
 the [*Cpp17RandomAccessIterator*](random.access.iterators#:Cpp17RandomAccessIterator "24.3.5.7 Random access iterators [random.access.iterators]") requirements ([[random.access.iterators]](random.access.iterators "24.3.5.7 Random access iterators"))
 unless PopulationIterator models [forward_iterator](iterator.concept.forward#concept:forward_iterator "24.3.4.11 Concept forward_­iterator [iterator.concept.forward]") ([[iterator.concept.forward]](iterator.concept.forward "24.3.4.11 Concept forward_­iterator"))[.](#alg.random.sample-2.3.sentence-1)

- [(2.4)](#alg.random.sample-2.4)

  remove_reference_t<UniformRandomBitGenerator> meets
 the requirements of a uniform random bit generator type ([[rand.req.urng]](rand.req.urng "29.5.3.3 Uniform random bit generator requirements"))[.](#alg.random.sample-2.4.sentence-1)

[3](#alg.random.sample-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8437)

*Effects*: Copies min(last - first, n) elements (the [*sample*](#def:sample "26.7.12 Sample [alg.random.sample]"))
from [first, last) (the [*population*](#def:population "26.7.12 Sample [alg.random.sample]")) to out such that each possible sample has equal probability of appearance[.](#alg.random.sample-3.sentence-1)

[*Note [1](#alg.random.sample-note-1)*:

Algorithms that obtain such effects include [*selection sampling*](#def:selection_sampling) and [*reservoir sampling*](#def:reservoir_sampling)[.](#alg.random.sample-3.sentence-2)

— *end note*]

[4](#alg.random.sample-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8447)

*Returns*: The end of the resulting sample range[.](#alg.random.sample-4.sentence-1)

[5](#alg.random.sample-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8451)

*Complexity*: O(last - first)[.](#alg.random.sample-5.sentence-1)

[6](#alg.random.sample-6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8455)

*Remarks*: 

- [(6.1)](#alg.random.sample-6.1)

  For the overload in namespace std,
 stable if and only if PopulationIterator models [forward_iterator](iterator.concept.forward#concept:forward_iterator "24.3.4.11 Concept forward_­iterator [iterator.concept.forward]")[.](#alg.random.sample-6.1.sentence-1)
  For the first overload in namespace ranges,
 stable if and only if I models [forward_iterator](iterator.concept.forward#concept:forward_iterator "24.3.4.11 Concept forward_­iterator [iterator.concept.forward]")[.](#alg.random.sample-6.1.sentence-2)

- [(6.2)](#alg.random.sample-6.2)

  To the extent that the implementation of this function makes use
 of random numbers, the object g serves as
 the implementation's source of randomness[.](#alg.random.sample-6.2.sentence-1)

### [26.7.13](#alg.random.shuffle) Shuffle [[alg.random.shuffle]](alg.random.shuffle)

[🔗](#lib:shuffle)

`template<class RandomAccessIterator, class UniformRandomBitGenerator>
  void shuffle(RandomAccessIterator first,
               RandomAccessIterator last,
               UniformRandomBitGenerator&& g);

template<[random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]") I, [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7 Concept sentinel_­for [iterator.concept.sentinel]")<I> S, class Gen>
  requires [permutable](alg.req.permutable#concept:permutable "24.3.7.6 Concept permutable [alg.req.permutable]")<I> &&
           [uniform_random_bit_generator](rand.req.urng#concept:uniform_random_bit_generator "29.5.3.3 Uniform random bit generator requirements [rand.req.urng]")<remove_reference_t<Gen>>
  I ranges::shuffle(I first, S last, Gen&& g);
template<[random_access_range](range.refinements#concept:random_access_range "25.4.6 Other range refinements [range.refinements]") R, class Gen>
  requires [permutable](alg.req.permutable#concept:permutable "24.3.7.6 Concept permutable [alg.req.permutable]")<iterator_t<R>> &&
           [uniform_random_bit_generator](rand.req.urng#concept:uniform_random_bit_generator "29.5.3.3 Uniform random bit generator requirements [rand.req.urng]")<remove_reference_t<Gen>>
  borrowed_iterator_t<R> ranges::shuffle(R&& r, Gen&& g);
`

[1](#alg.random.shuffle-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8491)

*Preconditions*: For the overload in namespace std:

- [(1.1)](#alg.random.shuffle-1.1)

  RandomAccessIterator meets
 the [*Cpp17ValueSwappable*](swappable.requirements#:Cpp17ValueSwappable "16.4.4.3 Swappable requirements [swappable.requirements]") requirements ([[swappable.requirements]](swappable.requirements "16.4.4.3 Swappable requirements"))[.](#alg.random.shuffle-1.1.sentence-1)

- [(1.2)](#alg.random.shuffle-1.2)

  The type remove_reference_t<UniformRandomBitGenerator> meets
 the uniform random bit generator ([[rand.req.urng]](rand.req.urng "29.5.3.3 Uniform random bit generator requirements")) requirements[.](#alg.random.shuffle-1.2.sentence-1)

[2](#alg.random.shuffle-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8503)

*Effects*: Permutes the elements in the range [first, last)
such that each possible permutation of those elements
has equal probability of appearance[.](#alg.random.shuffle-2.sentence-1)

[3](#alg.random.shuffle-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8509)

*Returns*: last for the overloads in namespace ranges[.](#alg.random.shuffle-3.sentence-1)

[4](#alg.random.shuffle-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8513)

*Complexity*: Exactly (last - first) - 1 swaps[.](#alg.random.shuffle-4.sentence-1)

[5](#alg.random.shuffle-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8517)

*Remarks*: To the extent that the implementation of this function makes use
of random numbers, the object referenced by g shall serve as
the implementation's source of randomness[.](#alg.random.shuffle-5.sentence-1)

### [26.7.14](#alg.shift) Shift [[alg.shift]](alg.shift)

[🔗](#lib:shift_left)

`template<class ForwardIterator>
  constexpr ForwardIterator
    shift_left(ForwardIterator first, ForwardIterator last,
               typename iterator_traits<ForwardIterator>::difference_type n);
template<class ExecutionPolicy, class ForwardIterator>
  ForwardIterator
    shift_left(ExecutionPolicy&& exec, ForwardIterator first, ForwardIterator last,
               typename iterator_traits<ForwardIterator>::difference_type n);

template<[permutable](alg.req.permutable#concept:permutable "24.3.7.6 Concept permutable [alg.req.permutable]") I, [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7 Concept sentinel_­for [iterator.concept.sentinel]")<I> S>
  constexpr subrange<I> ranges::shift_left(I first, S last, iter_difference_t<I> n);
template<[forward_range](range.refinements#concept:forward_range "25.4.6 Other range refinements [range.refinements]") R>
  requires [permutable](alg.req.permutable#concept:permutable "24.3.7.6 Concept permutable [alg.req.permutable]")<iterator_t<R>>
  constexpr borrowed_subrange_t<R> ranges::shift_left(R&& r, range_difference_t<R> n);

template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]") I, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<I> S>
  requires [permutable](alg.req.permutable#concept:permutable "24.3.7.6 Concept permutable [alg.req.permutable]")<I>
  subrange<I>
    ranges::shift_left(Ep&& exec, I first, S last, iter_difference_t<I> n);
template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6 Other range refinements [range.refinements]") R>
  requires [permutable](alg.req.permutable#concept:permutable "24.3.7.6 Concept permutable [alg.req.permutable]")<iterator_t<R>>
  borrowed_subrange_t<R>
    ranges::shift_left(Ep&& exec, R&& r, range_difference_t<R> n);
`

[1](#alg.shift-1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8554)

*Preconditions*: n >= 0 is true[.](#alg.shift-1.sentence-1)

For the overloads in namespace std,
the type of *first meets the [*Cpp17MoveAssignable*](utility.arg.requirements#:Cpp17MoveAssignable "16.4.4.2 Template argument requirements [utility.arg.requirements]") requirements[.](#alg.shift-1.sentence-2)

[2](#alg.shift-2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8560)

*Effects*: If n == 0 or n >= last - first, does nothing[.](#alg.shift-2.sentence-1)

Otherwise, moves the element
from position first + n + i into position first + i for each non-negative integer i < (last - first) - n[.](#alg.shift-2.sentence-2)

For the non-parallel algorithm overloads,
does so in order starting
from i = 0 and proceeding to i = (last - first) - n - 1[.](#alg.shift-2.sentence-3)

[3](#alg.shift-3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8571)

*Returns*: Let *NEW_LAST* be first + (last - first - n) if n < last - first,
otherwise first[.](#alg.shift-3.sentence-1)

Returns:

- [(3.1)](#alg.shift-3.1)

  *NEW_LAST* for the overloads in namespace std[.](#alg.shift-3.1.sentence-1)

- [(3.2)](#alg.shift-3.2)

  {first, *NEW_LAST*} for the overloads in namespace ranges[.](#alg.shift-3.2.sentence-1)

[4](#alg.shift-4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8585)

*Complexity*: At most (last - first) - n assignments[.](#alg.shift-4.sentence-1)

[🔗](#lib:shift_right)

`template<class ForwardIterator>
  constexpr ForwardIterator
    shift_right(ForwardIterator first, ForwardIterator last,
                typename iterator_traits<ForwardIterator>::difference_type n);
template<class ExecutionPolicy, class ForwardIterator>
  ForwardIterator
    shift_right(ExecutionPolicy&& exec, ForwardIterator first, ForwardIterator last,
                typename iterator_traits<ForwardIterator>::difference_type n);

template<[permutable](alg.req.permutable#concept:permutable "24.3.7.6 Concept permutable [alg.req.permutable]") I, [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7 Concept sentinel_­for [iterator.concept.sentinel]")<I> S>
  constexpr subrange<I> ranges::shift_right(I first, S last, iter_difference_t<I> n);
template<[forward_range](range.refinements#concept:forward_range "25.4.6 Other range refinements [range.refinements]") R>
  requires [permutable](alg.req.permutable#concept:permutable "24.3.7.6 Concept permutable [alg.req.permutable]")<iterator_t<R>>
  constexpr borrowed_subrange_t<R> ranges::shift_right(R&& r, range_difference_t<R> n);

template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_­access_­iterator [iterator.concept.random.access]") I, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_­sentinel_­for [iterator.concept.sizedsentinel]")<I> S>
  requires [permutable](alg.req.permutable#concept:permutable "24.3.7.6 Concept permutable [alg.req.permutable]")<I>
  subrange<I>
    ranges::shift_right(Ep&& exec, I first, S last, iter_difference_t<I> n);
template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6 Other range refinements [range.refinements]") R>
  requires [permutable](alg.req.permutable#concept:permutable "24.3.7.6 Concept permutable [alg.req.permutable]")<iterator_t<R>>
  borrowed_subrange_t<R>
    ranges::shift_right(Ep&& exec, R&& r, range_difference_t<R> n);
`

[5](#alg.shift-5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8618)

*Preconditions*: n >= 0 is true[.](#alg.shift-5.sentence-1)

For the overloads in namespace std,
the type of *first meets the [*Cpp17MoveAssignable*](utility.arg.requirements#:Cpp17MoveAssignable "16.4.4.2 Template argument requirements [utility.arg.requirements]") requirements,
and ForwardIterator meets
the [*Cpp17BidirectionalIterator*](bidirectional.iterators#:Cpp17BidirectionalIterator "24.3.5.6 Bidirectional iterators [bidirectional.iterators]") requirements ([[bidirectional.iterators]](bidirectional.iterators "24.3.5.6 Bidirectional iterators")) or
the [*Cpp17ValueSwappable*](swappable.requirements#:Cpp17ValueSwappable "16.4.4.3 Swappable requirements [swappable.requirements]") requirements[.](#alg.shift-5.sentence-2)

[6](#alg.shift-6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8627)

*Effects*: If n == 0 or n >= last - first, does nothing[.](#alg.shift-6.sentence-1)

Otherwise, moves the element
from position first + i into position first + n + i for each non-negative integer i < (last - first) - n[.](#alg.shift-6.sentence-2)

Does so in order starting
from i = (last - first) - n - 1 and proceeding to i = 0 if

- [(6.1)](#alg.shift-6.1)

for the non-parallel algorithm overload in namespace std,ForwardIterator meets the *Cpp17BidirectionalIterator* requirements,

- [(6.2)](#alg.shift-6.2)

for the non-parallel algorithm overloads in namespace ranges,I models [bidirectional_iterator](iterator.concept.bidir#concept:bidirectional_iterator "24.3.4.12 Concept bidirectional_­iterator [iterator.concept.bidir]")[.](#alg.shift-6.sentence-3)

[7](#alg.shift-7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8644)

*Returns*: Let *NEW_FIRST* be first + n if n < last - first,
otherwise last[.](#alg.shift-7.sentence-1)

Returns:

- [(7.1)](#alg.shift-7.1)

  *NEW_FIRST* for the overloads in namespace std[.](#alg.shift-7.1.sentence-1)

- [(7.2)](#alg.shift-7.2)

  {*NEW_FIRST*, last} for the overloads in namespace ranges[.](#alg.shift-7.2.sentence-1)

[8](#alg.shift-8)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L8657)

*Complexity*: At most (last - first) - n assignments or swaps[.](#alg.shift-8.sentence-1)