C ++：有没有办法限制对某些类的某些方法的访问，而不暴露其他私有成员？ [英] C++: Is there a way to limit access to certain methods to certain classes without exposing other private members?

问题描述

我有一个类有受保护的方法Zig :: punt（），我只想要它可以访问的类鳄梨。在C ++中，通常使用friend avocado说明符执行此操作，但这将导致所有其他变量可供Avocado类访问;我不想这样，因为这打破了封装。

I have a class with a protected method Zig::punt() and I only want it to be accessible to the class "Avocado". In C++, you'll normally do this using the "friend Avocado" specifier, but this will cause all of the other variables to become accessible to "Avocado" class; I don't want this because this breaks encapsulation.

是我不可能的，或者已经存在一个晦涩的技巧，我可以用来实现我想？

Is what I want impossible, or does there already exist an obscure trick out there that I can use to achieve what I want? Or possibly alternative class design patterns that'll achieve the same thing?

提前感谢任何想法！

推荐答案

这是一个丑陋但有效的方法：

Here's an ugly yet working trick:

class AvocadoFriender {
protected:
  virtual void punt() = 0;
  friend class Avocado; 
}

class Zig : public AvocadoFriender {
  ...
protected:
  void punt();
}

基本上你添加一个mixin类，只暴露界面的一部分，想要鳄梨。我们利用这样一个事实，通过继承一个与Avocado友好的类，除了最初暴露的内容之外，你不会暴露任何东西。

Basically you add a mixin class that exposes only the part of the interface that you want to Avocado. We take advantage of the fact that by inheriting a class that is befriended to Avocado you don't expose anything more except what was exposed originally.

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