Difference between revisions of "cpp/utility/tuple/forward as tuple"
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template< class... Types > | template< class... Types > | ||
| − | tuple<Types&&...> forward_as_tuple( Types&&... args ) noexcept; | + | std::tuple<Types&&...> forward_as_tuple( Types&&... args ) noexcept; |
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Revision as of 19:56, 2 November 2024
| Defined in header <tuple>
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| 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.
Contents |
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
| (C++11) |
creates a tuple object of the type defined by the argument types (function template) |
| (C++11) |
creates a tuple of lvalue references or unpacks a tuple into individual objects (function template) |
| (C++11) |
creates a tuple by concatenating any number of tuples (function template) |
| (C++17) |
calls a function with a tuple of arguments (function template) |
