constexpr piecewise_construct_t piecewise_construct = std::piecewise_construct_t(); | (since C++11) |
The constant std::piecewise_construct is an instance of an empty struct tag type std::piecewise_construct_t.
#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
| (C++11)
| tag type used to select correct function overload for piecewise construction (class) |
| constructs new pair (public member function of std::pair) |
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