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forward_as_tuple | ||||
(until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20) | ||||
| Helper concepts | ||||
(C++23) | ||||
| Helper classes | ||||
(C++23) | ||||
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| Deduction guides(C++17) |
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 inargs 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 |
| args | - | zero or more arguments to construct the tuple from |
Astd::tuple object created as if bystd::tuple<Types&&...>(std::forward<Types>(args)...)
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.
#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
(C++11) | creates atuple object of the type defined by the argument types(function template)[edit] |
(C++11) | creates atuple of lvalue references or unpacks a tuple into individual objects (function template)[edit] |
(C++11) | creates atuple by concatenating any number of tuples(function template)[edit] |
(C++17) | calls a function with a tuple of arguments (function template)[edit] |
