std::move_only_function::operator bool

 

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std::move_only_function

成员函数

move_only_function::move_only_function (C++23)

move_only_function::~move_only_function (C++23)

move_only_function::operator= (C++23)

move_only_function::swap (C++23)

move_only_function::operator bool (C++23)

move_only_function::operator() (C++23)

非成员函数

operator== (C++23)

swap(std::move_only_function) (C++23)

 

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

运行此代码

#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)