std::piecewise_construct_t
Defined in header <utility> | ||
---|---|---|
struct piecewise_construct_t { };
| (since C++11) (until C++17) | |
struct piecewise_construct_t { explicit piecewise_construct_t() = default; };
| (since C++17) |
std::piecewise_construct_t
is an empty struct tag type used to disambiguate between different functions that take two tuple arguments.
The overloads that do not use std::piecewise_construct_t
assume that each tuple argument becomes the element of a pair. The overloads that use std::piecewise_construct_t
assume that each tuple argument is used to construct, piecewise, a new object of specified type, which will become the element of the pair.
Example
#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
(C++11) | an object of type piecewise_construct_t used to disambiguate functions for piecewise construction (constant) |
constructs new pair (public member function of std::pair<T1,T2> ) |
© cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
http://en.cppreference.com/w/cpp/utility/piecewise_construct_t