Std::forward_as_tuple (3) Linux Manual Page

std::forward_as_tuple – std::forward_as_tuple

Synopsis

Defined in header <tuple>
template< class… Types > (since C++11)
tuple<Types&&…> forward_as_tuple( Types&&… args ) noexcept; (constexpr since C++14)
Constructs a tuple of references to the arguments in args suitable for forwarding as an argument to a function. The tuple has rvalue reference data members when rvalues are used as arguments, and otherwise has lvalue reference data members.

Parameters

args – zero or more arguments to construct the tuple from

Return value

A std::tuple object created as if by std::tuple<Types&&…>(std::forward<Types>(args)…)

Notes

If the arguments are temporaries, forward_as_tuple does not extend their lifetime; they have to be used before the end of the full expression.

Example

// Run this code

#include <iostream>

#include <map>

#include <tuple>

#include <string>
int main()

{
    std::map<int, std::string> m;
    m.emplace(std::piecewise_construct,
              std::forward_as_tuple(10),
              std::forward_as_tuple(20, 'a'));
    std::cout << "m[10] = " << m[10] << '\n';
    // The following is an error: it produces a
    // std::tuple<int&&, char&&> holding two dangling references.
    //
    // auto t = std::forward_as_tuple(20, 'a');
    // m.emplace(std::piecewise_construct, std::forward_as_tuple(10), t);
}

Output:

m[10] = aaaaaaaaaaaaaaaaaaaa

std::forward_as_tuple (3) Linux Manual Page