| 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.
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)...).
Exceptions
noexcept specification: noexceptNotes
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
#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
creates a tuple object of the type defined by the argument types (function template) | |
creates a tuple of lvalue references or unpacks a tuple into individual objects (function template) | |
creates a tuple by concatenating any number of tuples (function template) |
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