NAME

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 ) (constexpr since C++14)
noexcept;

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

See also

make_tuple creates a tuple object of the type defined by the argument types
(C++11) (function template)
tie creates a tuple of lvalue references or unpacks a tuple into individual
(C++11) objects
(function template)
tuple_cat creates a tuple by concatenating any number of tuples
(C++11) (function template)
apply calls a function with a tuple of arguments
(C++17) (function template)