# std::move_only_function::operator bool

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< cpp‎ | utility‎ | functional‎ | 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 otherwise.

### 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

operator bool | checks if a target is contained (public member function of `std::function<R(Args...)>`)

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