std::forward_as_tuple - cppreference.com (original) (raw)

| | | | | -------------------------------------------------------------------------------------------------------------------- | | ------------------------------------- | | 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.

[edit] Parameters

[edit] Return value

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

[edit] 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.

[edit] Example

#include #include #include #include   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:

[edit] See also

| | creates a tuple object of the type defined by the argument types (function template) [edit] | | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | | creates a tuple of lvalue references or unpacks a tuple into individual objects (function template) [edit] | | | creates a tuple by concatenating any number of tuples (function template) [edit] | | | calls a function with a tuple of arguments (function template) [edit] |