NAME¶

std::move_only_function::operator() - std::move_only_function::operator()

Synopsis¶

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.

// Run this code

#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¶

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