std::piecewise_construct (3) Linux Manual Page

std::piecewise_construct – std::piecewise_construct

Synopsis

constexpr piecewise_construct_t piecewise_construct         (since C++11)

= std::piecewise_construct_t();                             (until C++17)

inline constexpr piecewise_construct_t piecewise_construct  (since C++17)

= std::piecewise_construct_t();

The constant std::piecewise_construct is an instance of an empty struct tag type std::piecewise_construct_t.

Example

// Run this code

#include <iostream>

#include <utility>

#include <tuple>
struct Foo {
    Foo(std::tuple<int, float>)
    {
        std::cout << "Constructed a Foo from a tuple\n";
    }
    Foo(int, float)
    {
        std::cout << "Constructed a Foo from an int and a 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);
}

Output:

  Constructed a Foo from a tuple
  Constructed a Foo from a tuple
  Constructed a Foo from an int and a float
  Constructed a Foo from an int and a float

See also

piecewise_construct_t tag type used to select correct function overload for piecewise construction
                      (class)
(C++11)
                      constructs new pair
constructor (public member function of std::pair<T1,T2>)