# std::move_only_function<R(Args...) cv ref noexcept(noex)>::operator bool

< cpp‎ | utility‎ | functional‎ | move only function

explicit operator bool() const noexcept; |  | (C++23 起)

检查 *this 是否存储可调用目标，即非空。

### 参数

(none)

### 返回值

若 *this 存储可调用目标则为 true ，否则为 false 。

### 示例

    #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);
    }

输出：

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

### 参阅

operator bool | 检查是否包含了有效的目标 (`std::function<R(Args...)>` 的公开成员函数)