14 KiB
[tuple.cnstr]
22 General utilities library [utilities]
22.4 Tuples [tuple]
22.4.4 Class template tuple [tuple.tuple]
22.4.4.2 Construction [tuple.cnstr]
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.
For each tuple constructor, an exception is thrown only if the construction of one of the types in Types throws an exception.
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]).
The defaulted move and copy constructor of tuple<> are constexpr functions.
If is_trivially_destructible_v is true for all Ti, then the destructor of tuple is trivial.
The default constructor of tuple<> is trivial.
constexpr explicit(see below) tuple();
Constraints: is_default_constructible_v is true for all i.
Effects: Value-initializes each element.
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.
[Note 1:
This behavior can be implemented with a trait that checks whether a const Ti& can be initialized with {}.
â end note]
constexpr explicit(see below) tuple(const Types&...);
Constraints: sizeof...(Types) ⥠1 andis_copy_constructible_v is true for all i.
Effects: Initializes each element with the value of the corresponding parameter.
Remarks: The expression inside explicit is equivalent to:!conjunction_v<is_convertible<const Types&, Types>...>
template<class... UTypes> constexpr explicit(see below) tuple(UTypes&&... u);
Let disambiguating-constraint be:
negation<is_same<remove_cvref_t, tuple>> if sizeof...(Types) is 1;
otherwise,bool_constant<!is_same_v<remove_cvref_t, allocator_arg_t> || is_-
same_v<remove_cvref_t, allocator_arg_t>> if sizeof...(Types) is 2 or 3;
otherwise, true_type.
Constraints:
sizeof...(Types) equals sizeof...(UTypes),
sizeof...(Types) ⥠1, and
conjunction_v<disambiguating-constraint,
is_constructible<Types, UTypes>...> is
true.
Effects: Initializes the elements in the tuple with the corresponding value in std::forward(u).
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.
tuple(const tuple& u) = default;
Mandates: is_copy_constructible_v is true for all i.
Effects: Initializes each element of *this with the corresponding element of u.
tuple(tuple&& u) = default;
Constraints: is_move_constructible_v is true for all i.
Effects: For all i, initializes the ith element of *this withstd::forward(get(u)).
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);
Let I be the pack 0, 1, …, (sizeof...(Types) - 1).
Let FWD(u) be static_cast<decltype(u)>(u).
Constraints:
sizeof...(Types) equals sizeof...(UTypes), and
(is_constructible_v<Types, decltype(get(FWD(u)))> && ...) is true, and
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.
Effects: For all i, initializes the ith element of *this with get(FWD(u)).
Remarks: The expression inside explicit is equivalent to:!(is_convertible_v<decltype(get(FWD(u))), Types> && ...)
The constructor is defined as deleted if(reference_constructs_from_temporary_v<Types, decltype(get(FWD(u)))> || ...) is true.
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);
Let FWD(u) be static_cast<decltype(u)>(u).
Constraints:
sizeof...(Types) is 2,
is_constructible_v<T0, decltype(get<0>(FWD(u)))> is true, and
is_constructible_v<T1, decltype(get<1>(FWD(u)))> is true.
Effects: Initializes the first element with get<0>(FWD(u)) and the second element with get<1>(FWD(u)).
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.
template<[tuple-like](tuple.like#concept:tuple-like "22.4.3 Concept tuple-like [tuple.like]") UTuple> constexpr explicit(see below) tuple(UTuple&& u);
Let I be the pack 0, 1, …, (sizeof...(Types) - 1).
Constraints:
different-from<UTuple, tuple> ([range.utility.helpers]) is true,
remove_cvref_t is not a specialization of ranges::subrange,
sizeof...(Types) equals tuple_size_v<remove_cvref_t>,
(is_constructible_v<Types, decltype(get(std::forward(u)))> && ...) istrue, and
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.
Effects: For all i, initializes the ith element of *this withget(std::forward(u)).
Remarks: The expression inside explicit is equivalent to:!(is_convertible_v<decltype(get(std::forward(u))), Types> && ...)
The constructor is defined as deleted if(reference_constructs_from_temporary_v<Types, decltype(get(std::forward(u)))>|| ...) is true.
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&&);
Preconditions: Alloc meets the Cpp17Allocator requirements ([allocator.requirements.general]).
Effects: Equivalent to the preceding constructors except that each element is constructed withuses-allocator construction.