NAME¶

std::reference_wrapper::operator() - std::reference_wrapper::operator()

Synopsis¶

template< class... ArgTypes >
(since C++11)
typename std::result_of<T&(ArgTypes&&...)>::type (until C++17)

operator() ( ArgTypes&&... args ) const;
template< class... ArgTypes >
(since C++17)
std::invoke_result_t<T&, ArgTypes...> (constexpr since
C++20)
operator() ( ArgTypes&&... args ) const noexcept(/* see below
*/);

Calls the Callable object, reference to which is stored, as if by INVOKE(get(),
std::forward<ArgTypes>(args)...). This function is available only if the stored
reference points to a Callable object.

T must be a complete type.

Parameters¶

args - arguments to pass to the called function

Return value¶

The return value of the called function.

Exceptions¶

May throw implementation-defined exceptions. (since C++11)
(until C++17)
noexcept specification: (since C++17)
noexcept(std::is_nothrow_invocable_v<T&, ArgTypes...>)

Example¶

// Run this code

#include <functional>
#include <iostream>

void f1()
{
std::cout << "reference to function called\n";
}

void f2(int n)
{
std::cout << "bind expression called with " << n << " as the argument\n";
}

int main()
{
std::reference_wrapper<void()> ref1 = std::ref(f1);
ref1();

auto b = std::bind(f2, std::placeholders::_1);
auto ref2 = std::ref(b);
ref2(7);

auto c = []{ std::cout << "lambda function called\n"; };
auto ref3 = std::ref(c);
ref3();
}

Output:¶

reference to function called
bind expression called with 7 as the argument
lambda function called

Defect reports

The following behavior-changing defect reports were applied retroactively to
previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 3764 C++17 operator() is not noexcept propagate noexcept

See also¶

get accesses the stored reference
operator T& (public member function)

Category:¶

* conditionally noexcept