std::piecewise_construct_t

`<utility>`
`struct piecewise_construct_t { explicit piecewise_construct_t() = default; };`		( C++11)
`constexpr std::piecewise_construct_t piecewise_construct{};`		( C++11) ( C++17)
`inline constexpr std::piecewise_construct_t piecewise_construct{};`		( C++17)

std::piecewise_construct_t , , . std::piecewise_construct .

, std::piecewise_construct_t, , . , std::piecewise_construct_t, , , .

[edit]

#include <iostream>
#include <utility>
#include <tuple>

struct Foo {
    Foo(std::tuple<int, float>) 
    {
        std::cout << " Foo  tuple\n";
    }
    Foo(int, float) 
    {
        std::cout << " Foo  int  float\n";
    }
};

int main()
{
    std::tuple<int, float> t(1, 3.14);
    std::pair<Foo, Foo> p1(t, t);
    std::pair<Foo, Foo> p2(std::piecewise_construct, t, t);
}

:

 Foo  tuple
 Foo  tuple
 Foo  int  float
 Foo  int  float

C++:


LWG 2510	C++11	,

()	pair (public - `std::pair`)







(C++20)

(C++20)
(C++11)





(C++20)


/

(C++11)
(C++11)
(C++11)
(C++17)

-
pair::pair
pair::operator=
pair::swap (C++11)
,
make_pair
operator==operator!=operator<operator<=operator>operator>=operator<=> ( C++20)( C++20)( C++20)( C++20)( C++20)(C++20)
std::swap (C++11)
get (C++11)
(C++17)

tuple_size (C++11)
tuple_element (C++11)
basic_common_reference (C++23)
common_type (C++23)
piecewise_construct_t (C++11)

cppreference.com

std::piecewise_construct_t