std::forward_as_tuple

 

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Defined in header <tuple>
template<class... Types> std::tuple<Types&&...> forward_as_tuple( Types&&... args)noexcept;		(since C++11) (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 <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);}

Output:

m[6] = ggggggggg

See also

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