指向类模板成员的函数指针 [英] Function pointer to class template member

问题描述

我上了这堂课:

template <class T>
class list
{
    ...
    bool moreThan(T x, T y);
    bool lessThan(T x, T y);
    ...
};

我需要一个函数指针来更改类的行为，并在使用bool moreThan(T, T)或bool lessThan(T, T)之间进行切换. 所以我目前正在使用:

I need a function pointer to change the behavior of my class, and switch between using bool moreThan(T, T) or bool lessThan(T, T). So I'm currently using:

bool (list<int>::*foo)(int x, int y);
foo = &list<int>::lessThan;

并使用它:

(this->*foo)(x, y);

，但是我想有一个灵活的函数指针，这样我就可以将其与我需要的任何T一起使用，而不仅仅是int.那么有没有办法创建指向类模板成员的函数指针呢?像这样:

but I would like to have a flexible function pointer, so that I can use it with whichever T I need, not just int. So is there a way to create a function pointer to a class template member? Something like:

template <class T>
bool (list<T>::*foo)(T x, T y); //this doesn't work

推荐答案

没有.指向成员的指针必须指向某物.类模板中的成员函数不是单个函数，而是一系列函数-每个函数都有不同的类型.甚至可能存在T，而list<T>::lessThan并不存在，或者是类型还是变量！

No there isn't. A pointer-to-member has to point to something. A member function in a class template isn't a single function, it's a family of functions - and each one has a different type. There could even be a T for which list<T>::lessThan doesn't exist, or is a type or a variable!

如果我们为这样一个指向成员的指针做了别名:

If we made an alias for one such pointer to member:

template <typename T>
using CompFun = bool (list<T>::*)(T, T);

然后很明显CompFun<int>和CompFun<string>是不同的类型.您不能创建通用的CompFun<T>变量.

Then it's obvious that CompFun<int> and CompFun<string> are different types. You cannot create a generic CompFun<T> variable.

但是，根据您要尝试执行的操作，可能有一种很好的方法来完成该操作.

Depending on what it is you're trying to do, though, there might be a good way to accomplish that.

这篇关于指向类模板成员的函数指针的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！