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std::forward_as_tuple

Defined in header `<tuple>`
template< class... Types > tuple<Types&&...> forward_as_tuple( Types&&... args );		(since C++11) (until C++14)
template< class... Types > constexpr tuple<Types&&...> forward_as_tuple( Types&&... args );		(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)...).

Exceptions

noexcept specification:

noexcept

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 <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

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