std::move_only_function::operator bool

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std::move_only_function
explicit operator bool ( ) const noexcept ;
(since C++23)

Checks whether *this stores a callable target, i.e. is not empty.

Parameters

(none)

Return value

true if *this stores a callable target, false

Example

Run this code
#include <functional>
#include <iostream>
 
void sampleFunction()
{
    std::cout << "This is the sample function!\n";
}
 
void checkFunc(std::move_only_function<void() const> const& func)
{
    // Use operator bool to determine if callable target is available.
    if (func)
    {
        std::cout << "Function is not empty! Calling function.\n";
        func();
    }
    else
        std::cout << "Function is empty. Nothing to do.\n";
}
 
int main()
{
    std::move_only_function<void() const> f1{};
    std::move_only_function<void() const> f2{sampleFunction};
 
    std::cout << "f1: ";
    checkFunc(f1);
 
    std::cout << "f2: ";
    checkFunc(f2);
}

Output: 

f1: Function is empty. Nothing to do.
f2: Function is not empty! Calling function.
This is the sample function!

See also

(C++23)
 compares a std::move_only_function with nullptr
(function)
checks if a target is contained
(public member function of std::function<R(Args...)>)
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