std::piecewise_construct (3) - Linux Manuals

std::piecewise_construct: std::piecewise_construct

NAME

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