std::forward_as_tuple

From Cppreference

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. If rvalues are used, the result of this function must be consumed before the next sequence point.

[edit] Parameters

[edit] Return value

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

[edit] Exceptions

[edit] Example

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

Output:

m[10] = aaaaaaaaaaaaaaaaaaaa