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std::reference_wrapper<T>::operator()

From cppreference.com
 
 
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Old binders and adaptors
(until C++17*)
(until C++17*)
(until C++17*)
(until C++17*)  
(until C++17*)
(until C++17*)(until C++17*)(until C++17*)(until C++17*)
(until C++20*)
(until C++20*)
(until C++17*)(until C++17*)
(until C++17*)(until C++17*)

(until C++17*)
(until C++17*)(until C++17*)(until C++17*)(until C++17*)
(until C++20*)
(until C++20*)
 
 
template< class... ArgTypes >

typename std::result_of<T&(ArgTypes&&...)>::type

    operator() ( ArgTypes&&... args ) const;
(since C++11)
(until C++17)
template< class... ArgTypes >

std::invoke_result_t<T&, ArgTypes...>

    operator() ( ArgTypes&&... args ) const noexcept(/* see below */);
(since C++17)
(constexpr since C++20)

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.

Contents

[edit] Parameters

args - arguments to pass to the called function

[edit] Return value

The return value of the called function.

[edit] Exceptions

May throw implementation-defined exceptions.

(since C++11)
(until C++17)
noexcept specification:  
noexcept(std::is_nothrow_invocable_v<T&, ArgTypes...>)
(since C++17)

[edit] Example

#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

[edit] 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

[edit] See also

accesses the stored reference
(public member function) [edit]