[tuple.cnstr]

# 22 General utilities library [[utilities]](./#utilities)

## 22.4 Tuples [[tuple]](tuple#cnstr)

### 22.4.4 Class template tuple [[tuple.tuple]](tuple.tuple#tuple.cnstr)

#### 22.4.4.2 Construction [tuple.cnstr]

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L1788)

In the descriptions that follow, let i be in the range
[0, sizeof...(Types)) in order, Ti be the ith type in Types, andUi be the ith type in a template parameter pack named UTypes, where indexing
is zero-based[.](#1.sentence-1)

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L1795)

For each tuple constructor, an exception is thrown only if the construction of
one of the types in Types throws an exception[.](#2.sentence-1)

[3](#3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L1799)

The defaulted move and copy constructor, respectively, oftuple is a constexpr function if and only if all
required element-wise initializations for move and copy, respectively,
would be constexpr-suitable ([[dcl.constexpr]](dcl.constexpr "9.2.6 The constexpr and consteval specifiers"))[.](#3.sentence-1)

The defaulted move and copy constructor of tuple<> are
constexpr functions[.](#3.sentence-2)

[4](#4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L1807)

If is_trivially_destructible_v<Ti> is true for all Ti,
then the destructor of tuple is trivial[.](#4.sentence-1)

[5](#5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L1811)

The default constructor of tuple<> is trivial[.](#5.sentence-1)

[ð](#lib:tuple,constructor)

`constexpr explicit(see below) tuple();
`

[6](#6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L1820)

*Constraints*: is_default_constructible_v<Ti> is true for all i[.](#6.sentence-1)

[7](#7)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L1824)

*Effects*: Value-initializes each element[.](#7.sentence-1)

[8](#8)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L1828)

*Remarks*: The expression inside explicit evaluates to true if and only if Ti is not
copy-list-initializable from an empty list
for at least one i[.](#8.sentence-1)

[*Note [1](#note-1)*:

This behavior can be implemented with a trait that checks whether
a const Ti& can be initialized with {}[.](#8.sentence-2)

â *end note*]

[ð](#lib:tuple,constructor_)

`constexpr explicit(see below) tuple(const Types&...);
`

[9](#9)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L1846)

*Constraints*: sizeof...(Types) â¥ 1 andis_copy_constructible_v<Ti> is true for all i[.](#9.sentence-1)

[10](#10)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L1851)

*Effects*: Initializes each element with the value of the
corresponding parameter[.](#10.sentence-1)

[11](#11)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L1856)

*Remarks*: The expression inside explicit is equivalent to:!conjunction_v<is_convertible<const Types&, Types>...>

[ð](#lib:tuple,constructor__)

`template<class... UTypes> constexpr explicit(see below) tuple(UTypes&&... u);
`

[12](#12)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L1870)

Let *disambiguating-constraint* be:

- [(12.1)](#12.1)

negation<is_same<remove_cvref_t<U0>, tuple>> if sizeof...(Types) is 1;

- [(12.2)](#12.2)

otherwise,bool_constant<!is_same_v<remove_cvref_t<U0>, allocator_arg_t> || is_-  
same_v<remove_cvref_t<T0>, allocator_arg_t>> if sizeof...(Types) is 2 or 3;

- [(12.3)](#12.3)

otherwise, true_type[.](#12.sentence-1)

[13](#13)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L1885)

*Constraints*: 

- [(13.1)](#13.1)

sizeof...(Types) equals sizeof...(UTypes),

- [(13.2)](#13.2)

sizeof...(Types) â¥ 1, and

- [(13.3)](#13.3)

conjunction_v<*disambiguating-constraint*,
is_constructible<Types, UTypes>...> is  
true[.](#13.sentence-1)

[14](#14)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L1897)

*Effects*: Initializes the elements in the tuple with the
corresponding value in std​::​forward<UTypes>(u)[.](#14.sentence-1)

[15](#15)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L1902)

*Remarks*: The expression inside explicit is equivalent to:!conjunction_v<is_convertible<UTypes, Types>...>

This constructor is defined as deleted if(reference_constructs_from_temporary_v<Types, UTypes&&> || ...) is true[.](#15.sentence-2)

[ð](#lib:tuple,constructor___)

`tuple(const tuple& u) = default;
`

[16](#16)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L1921)

*Mandates*: is_copy_constructible_v<Ti> is true for all i[.](#16.sentence-1)

[17](#17)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L1925)

*Effects*: Initializes each element of *this with the
corresponding element of u[.](#17.sentence-1)

[ð](#lib:tuple,constructor____)

`tuple(tuple&& u) = default;
`

[18](#18)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L1937)

*Constraints*: is_move_constructible_v<Ti> is true for all i[.](#18.sentence-1)

[19](#19)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L1941)

*Effects*: For all i, initializes the ith element of *this withstd​::​forward<Ti>(get<i>(u))[.](#19.sentence-1)

[ð](#lib:tuple,constructor_____)

`template<class... UTypes> constexpr explicit(see below) tuple(tuple<UTypes...>& u);
template<class... UTypes> constexpr explicit(see below) tuple(const tuple<UTypes...>& u);
template<class... UTypes> constexpr explicit(see below) tuple(tuple<UTypes...>&& u);
template<class... UTypes> constexpr explicit(see below) tuple(const tuple<UTypes...>&& u);
`

[20](#20)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L1956)

Let I be the pack 0, 1, …, (sizeof...(Types) - 1)[.](#20.sentence-1)

  
Let *FWD*(u) be static_cast<decltype(u)>(u)[.](#20.sentence-2)

[21](#21)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L1960)

*Constraints*: 

- [(21.1)](#21.1)

sizeof...(Types) equals sizeof...(UTypes), and

- [(21.2)](#21.2)

(is_constructible_v<Types, decltype(get<I>(*FWD*(u)))> && ...) is true, and

- [(21.3)](#21.3)

either sizeof...(Types) is not 1, or
(when Types... expands to T andUTypes... expands to U)is_convertible_v<decltype(u), T>,is_constructible_v<T, decltype(u)>, andis_same_v<T, U> are all false[.](#21.sentence-1)

[22](#22)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L1977)

*Effects*: For all i, initializes the ith element of *this with get<i>(*FWD*(u))[.](#22.sentence-1)

[23](#23)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L1982)

*Remarks*: The expression inside explicit is equivalent to:!(is_convertible_v<decltype(get<I>(*FWD*(u))), Types> && ...)

The constructor is defined as deleted if(reference_constructs_from_temporary_v<Types, decltype(get<I>(*FWD*(u)))> || ...) is true[.](#23.sentence-2)

[ð](#lib:tuple,constructor______)

`template<class U1, class U2> constexpr explicit(see below) tuple(pair<U1, U2>& u);
template<class U1, class U2> constexpr explicit(see below) tuple(const pair<U1, U2>& u);
template<class U1, class U2> constexpr explicit(see below) tuple(pair<U1, U2>&& u);
template<class U1, class U2> constexpr explicit(see below) tuple(const pair<U1, U2>&& u);
`

[24](#24)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L2004)

Let *FWD*(u) be static_cast<decltype(u)>(u)[.](#24.sentence-1)

[25](#25)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L2007)

*Constraints*: 

- [(25.1)](#25.1)

sizeof...(Types) is 2,

- [(25.2)](#25.2)

is_constructible_v<T0, decltype(get<0>(*FWD*(u)))> is true, and

- [(25.3)](#25.3)

is_constructible_v<T1, decltype(get<1>(*FWD*(u)))> is true[.](#25.sentence-1)

[26](#26)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L2018)

*Effects*: Initializes the first element with get<0>(*FWD*(u)) and
the second element with get<1>(*FWD*(​u))[.](#26.sentence-1)

[27](#27)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L2023)

*Remarks*: The expression inside explicit is equivalent to:!is_convertible_v<decltype(get<0>(*FWD*(u))), T0> ||!is_convertible_v<decltype(get<1>(*FWD*(u))), T1>

The constructor is defined as deleted ifreference_constructs_from_temporary_v<T0, decltype(get<0>(*FWD*(u)))> || reference_constructs_from_temporary_v<T1, decltype(get<1>(*FWD*(u)))> is true[.](#27.sentence-2)

[ð](#lib:tuple,constructor_______)

`template<[tuple-like](tuple.like#concept:tuple-like "22.4.3 Concept tuple-like [tuple.like]") UTuple>
  constexpr explicit(see below) tuple(UTuple&& u);
`

[28](#28)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L2045)

Let I be the pack 0, 1, …, (sizeof...(Types) - 1)[.](#28.sentence-1)

[29](#29)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L2048)

*Constraints*: 

- [(29.1)](#29.1)

[*different-from*](range.utility.helpers#concept:different-from "25.5.2 Helper concepts [range.utility.helpers]")<UTuple, tuple> ([[range.utility.helpers]](range.utility.helpers "25.5.2 Helper concepts"))
is true,

- [(29.2)](#29.2)

remove_cvref_t<UTuple> is not a specialization of ranges​::​subrange,

- [(29.3)](#29.3)

sizeof...(Types) equals tuple_size_v<remove_cvref_t<UTuple>>,

- [(29.4)](#29.4)

(is_constructible_v<Types, decltype(get<I>(std​::​forward<UTuple>(u)))> && ...) istrue, and

- [(29.5)](#29.5)

either sizeof...(Types) is not 1, or
(when Types... expands to T)is_convertible_v<UTuple, T> andis_constructible_v<T, UTuple> are both false[.](#29.sentence-1)

[30](#30)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L2075)

*Effects*: For all i, initializes the ith element of *this withget<i>(std​::​forward<UTuple>(u))[.](#30.sentence-1)

[31](#31)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L2080)

*Remarks*: The expression inside explicit is equivalent to:!(is_convertible_v<decltype(get<I>(std::forward<UTuple>(u))), Types> && ...)

The constructor is defined as deleted if(reference_constructs_from_temporary_v<Types, decltype(get<I>(std::forward<UTuple>(u)))>|| ...) is true[.](#31.sentence-2)

[ð](#lib:tuple,constructor________)

`template<class Alloc>
  constexpr explicit(see below)
    tuple(allocator_arg_t, const Alloc& a);
template<class Alloc>
  constexpr explicit(see below)
    tuple(allocator_arg_t, const Alloc& a, const Types&...);
template<class Alloc, class... UTypes>
  constexpr explicit(see below)
    tuple(allocator_arg_t, const Alloc& a, UTypes&&...);
template<class Alloc>
  constexpr tuple(allocator_arg_t, const Alloc& a, const tuple&);
template<class Alloc>
  constexpr tuple(allocator_arg_t, const Alloc& a, tuple&&);
template<class Alloc, class... UTypes>
  constexpr explicit(see below)
    tuple(allocator_arg_t, const Alloc& a, tuple<UTypes...>&);
template<class Alloc, class... UTypes>
  constexpr explicit(see below)
    tuple(allocator_arg_t, const Alloc& a, const tuple<UTypes...>&);
template<class Alloc, class... UTypes>
  constexpr explicit(see below)
    tuple(allocator_arg_t, const Alloc& a, tuple<UTypes...>&&);
template<class Alloc, class... UTypes>
  constexpr explicit(see below)
    tuple(allocator_arg_t, const Alloc& a, const tuple<UTypes...>&&);
template<class Alloc, class U1, class U2>
  constexpr explicit(see below)
    tuple(allocator_arg_t, const Alloc& a, pair<U1, U2>&);
template<class Alloc, class U1, class U2>
  constexpr explicit(see below)
    tuple(allocator_arg_t, const Alloc& a, const pair<U1, U2>&);
template<class Alloc, class U1, class U2>
  constexpr explicit(see below)
    tuple(allocator_arg_t, const Alloc& a, pair<U1, U2>&&);
template<class Alloc, class U1, class U2>
  constexpr explicit(see below)
    tuple(allocator_arg_t, const Alloc& a, const pair<U1, U2>&&);
template<class Alloc, [tuple-like](tuple.like#concept:tuple-like "22.4.3 Concept tuple-like [tuple.like]") UTuple>
  constexpr explicit(see below)
    tuple(allocator_arg_t, const Alloc& a, UTuple&&);
`

[32](#32)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L2139)

*Preconditions*: Alloc meets
the [*Cpp17Allocator*](allocator.requirements.general#:Cpp17Allocator "16.4.4.6.1 General [allocator.requirements.general]") requirements ([[allocator.requirements.general]](allocator.requirements.general "16.4.4.6.1 General"))[.](#32.sentence-1)

[33](#33)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/utilities.tex#L2144)

*Effects*: Equivalent to the preceding constructors except that each element is constructed with[uses-allocator construction](allocator.uses.construction#def:uses-allocator_construction "20.2.8.2 Uses-allocator construction [allocator.uses.construction]")[.](#33.sentence-1)
