C ++类设计问题 [英] C++ class design questions

问题描述

我有一个类Node。此类可以添加或删除与其自身相关的其他节点。节点由List类使用。为了防止节点在使用期间直接（在外部，而不是由适当的类）修改，并导致List类出现问题，节点添加/删除功能是受保护的或私有的。这需要List类是Node的朋友。

I have a class Node. This class can add or remove other nodes relative to itself. Node is used by a List class. To prevent the nodes being modified directly (externally, IE not by the appropriate classes) during usage and causing problems with the List class, the nodes add/remove functions are either protected or private. This requires that List class is a friend to Node.

但是，这个问题是List类本身是其他子类的模板类，添加原型/为每个子类添加friend关键字显然不是最好的解决方案。

However, the problem with this is that the List class itself is a template class for other subclasses, and adding prototyping/adding the friend keyword for each subclass is clearly not the best solution.

我如何设计Node和List类/子类，以便：

How would I design the Node and List class/subclasses so that:

• 节点不能由外部构造，只用特定的类/子类构造？


• 节点可以构造/删除其他节点


• 节点函数只能访问特定类（列表，列表子类和列表辅助类 - 列表帮助类不是列表的子类）？


• 列表，列表子类和列表辅助类可以直接修改或间接修改Node的非公开变量
/ li>

• Node cannot be constructed by itself externally, is only constructed with specific classes/subclasses?
• Node can construct/remove other nodes given above?
• Node functions are only accessible to specific classes (List, list subclasses, and list helper classes - list helper classes are not subclasses of list)?
• The node variable (Item) is publicly accessible give above?
• List, list subclasses and list helper classes can directly modify or indirectly modify the non-public variables of Node?

这些是否可能，如果可能，如何？

Are these possible, and if so, how?

推荐答案

我会使 Node 一个受保护的嵌套类列表：

I would make Node a protected nested class of List:

class List
{
    ...
    protected:
        class Node
        {
            ...
        };
};

这样，只有List和它的子类可以访问它。 由于它嵌套在 List 中，list可以访问其私有/ protected成员和函数。它还有助于突出两个类之间的函数关系。

This way, only List and its subclasses can access it. Since it is nested within List, list may access its private/protected members and functions. It also helps to highlight the functional relationship between the two classes. This probably takes care of all your dot points except the third.

编辑仔细检查我的事实，看起来在C ++封装类不要拥有对嵌套类成员的特殊访问权限（看起来是一个Java东西），请参阅此处。因此，您需要使节点成员公开，但我仍然认为此解决方案鼓励良好的封装。

EDIT double checking my facts, it seems that in C++ enclosing classes do not have special access permissions to nested class members after all (seems that's a Java thing), see here. As such, you will need to make Node members public, but I still think this solution encourages good encapsulation.

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