std::move_only_function::operator()

From cppreference.com
 
 
Utilities library
General utilities
Date and time
Function objects
Formatting library (C++20)
(C++11)
Relational operators (deprecated in C++20)
Integer comparison functions
(C++20)(C++20)(C++20)   
(C++20)
Swap and type operations
(C++14)
(C++11)
(C++11)
(C++11)
(C++17)
Common vocabulary types
(C++11)
(C++17)
(C++17)
(C++17)
(C++11)
(C++17)
(C++23)
Elementary string conversions
(C++17)
(C++17)
 
Function objects
Function wrappers
(C++11)
(C++11)
Partial function application
(C++20)(C++23)
(C++11)
Function invocation
(C++17)(C++23)
Identity function object
(C++20)
Reference wrappers
(C++11)(C++11)
Transparent operator wrappers
(C++14)
(C++14)
(C++14)
(C++14)
(C++14)
(C++14)
(C++14)
(C++14)
(C++14)
(C++14)
(C++14)
(C++14)
Negators
(C++17)
Searchers
Constrained comparators
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++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)
 
 
R operator()( Args... args ) /*cv*/ /*ref*/ noexcept(/*noex*/);
(since C++23)

Invokes the stored callable target with the parameters args. The /*cv*/, /*ref*/, and /*noex*/ parts of operator() are identical to those of the template parameter of std::move_only_function.

Equivalent to return std::invoke_r<R>(/*cv-ref-cast*/(f), std::forward<Args>(args)...);, where f is a cv-unqualified lvalue that denotes the target object of *this, and /*cv-ref-cast*/(f) is equivalent to:

  • f if cv ref is either empty or &, or
  • std::as_const(f) if cv ref is either const or const &, or
  • std::move(f) if cv ref is &&, or
  • std::move(std::as_const(f)) if cv ref is const &&.

The behavior is undefined if *this is empty.

Parameters

args - parameters to pass to the stored callable target

Return value

std::invoke_r<R>(/*cv-ref-cast*/(f), std::forward<Args>(args)...).

Exceptions

Propagates the exception thrown by the underlying function call.

Example

The following example shows how std::move_only_function can passed to other functions by value. Also, it shows how std::move_only_function can store lambdas.

#include <iostream>
#include <functional>
 
void call(std::move_only_function<int() const> f)  // can be passed by value
{ 
    std::cout << f() << '\n';
}
 
int normal_function() 
{
    return 42;
}
 
int main()
{
    int n = 1;
    auto lambda = [&n](){ return n; };
    std::move_only_function<int() const> f = lambda;
    call(std::move(f));
 
    n = 2;
    call(lambda); 
 
    f = normal_function; 
    call(std::move(f));
}

Output:

1
2
42

See also

invokes the target
(public member function of std::function<R(Args...)>)
calls the stored function
(public member function of std::reference_wrapper<T>)
(C++17)(C++23)
invokes any Callable object with given arguments and possibility to specify return type (since C++23)
(function template)