是否有一个std :: function的用例不被函数指针覆盖，还是只是语法糖？ [英] Is there a use case for std::function that is not covered by function pointers, or is it just syntactic sugar?

问题描述

与函数指针相比​​，std :: function的符号是相当不错的。但是，除此之外，我找不到一个用例，它不能被指针替换。因此，它只是函数指针的语法糖？

The notation for std::function is quite nice when compared to function pointers. However, other than that, I can't find a use case where it couldn't be replaced by pointers. So is it just syntactic sugar for function pointers?

推荐答案

std :: function< code>提供了封装任何类型的可调用对象的可能性，这是函数指针不能做的事情（尽管非捕获 lambdas可以转换为函数指针）。

std::function<> gives you the possibility of encapsulating any type of callable object, which is something function pointers cannot do (although it is true that non-capturing lambdas can be converted to function pointers).

为了让您了解您可以实现的灵活性：

To give you an idea of the kind of flexibility it allows you to achieve:

#include <functional>
#include <iostream>
#include <vector>

// A functor... (could even have state!)
struct X
{
    void operator () () { std::cout << "Functor!" << std::endl; }
};

// A regular function...
void bar()
{
    std::cout << "Function" << std::endl;
}

// A regular function with one argument that will be bound...
void foo(int x)
{
    std::cout << "Bound Function " << x << "!" << std::endl;
}

int main()
{
    // Heterogenous collection of callable objects
    std::vector<std::function<void()>> functions;

    // Fill in the container...
    functions.push_back(X());
    functions.push_back(bar);
    functions.push_back(std::bind(foo, 42));

    // And a add a lambda defined in-place as well...
    functions.push_back([] () { std::cout << "Lambda!" << std::endl; });

    // Now call them all!
    for (auto& f : functions)
    {
        f(); // Same interface for all kinds of callable object...
    }
}

照常，请参阅此处的示例。除此之外，您还可以实现命令模式。

As usual, see a live example here. Among other things, this allows you to realize the Command Pattern.

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