std::forward_as_tuple

Header: <tuple>

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.

# Declarations

template< class... Types >
std::tuple<Types&&...> forward_as_tuple( Types&&... args ) noexcept;

(since C++11) (constexpr since C++14)

# Parameters

# Return value

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

#include <iostream>
#include <map>
#include <string>
#include <tuple>
 
int main()
{
    std::map<int, std::string> m;
 
    m.emplace(std::piecewise_construct,
              std::forward_as_tuple(6),
              std::forward_as_tuple(9, 'g'));
    std::cout << "m[6] = " << m[6] << '\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);
}

# See also