std::forward_as_tuple
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                    | 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.
| Contents | 
[edit] Parameters
| args | - | zero or more arguments to construct the tuple from | 
[edit] Return value
A std::tuple object created as if by std::tuple<Types&&...>(std::forward<Types>(args)...)
[edit] Exceptions
noexcept specification:  
noexcept
  [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
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
[edit] See also
| creates a tupleobject of the type defined by the argument types(function template) | |
| creates a tupleof lvalue references or unpacks a tuple into individual objects(function template) | |
| creates a tupleby concatenating any number of tuples(function template) | |
| (C++17) | calls a function with a tuple of arguments (function template) | 


