朋友类有限的访问 [英] friend class with limited access

问题描述

我想创建一个类A类B的朋友类。我想这样做，因为这些交互非常多，A需要更改类B的内部（我不想公开使用公共）。

例如：

pre> class A
{
};

class B
{
private：
void setState（）;
void setFlags（）;
friend class A
};


我想A能够访问setState但不能setFlags ...有一个设计模式

感谢

解决方案

这取决于你的意思是一个很好的方式:)在comp.lang.c ++。moderated我们有同样的问题一个时间前。您可以看到它生成的讨论 。

IIRC，我们最终使用嵌套键的朋友方法。应用于您的示例，这将产生：

 类A 
 {
} 
 
 class B 
 {
 public：
 class Key {
 friend class A; 
 Key（）; 
}; 
 
 void setFlags（Key）{setFlags（）;} 
 
 private：
 void setState（）; 
 void setFlags（）; 
}; 
  

想法是public setFlags（）必须用Key调用，的Key可以创建一个，因为它的ctor是私有的。

I want to make a class A friend class of class B. I want to do this as these interact very much and A needs to change internals of class B (which I dont want to expose using public). But I want to make sure it has access to only a few selected functions not all the functions.

Example:

class A
{
};

class B
{
private:
 void setState();
void setFlags();
friend class A
};

I want A to be able to access setState but not setFlags... Is there a design pattern or a nice way of doing this or am I left with giving full access or no access at all in this case.

Thanks

解决方案

It depends on what you mean by "a nice way" :) At comp.lang.c++.moderated we had the same question a while ago. You may see the discussion it generated there.

IIRC, we ended up using the "friend of a nested key" approach. Applied to your example, this would yield:

class A
{
};

class B
{
public:
     class Key{
         friend class A;
         Key();
     };

    void setFlags(Key){setFlags();}         

private:
  void setState();
  void setFlags();
};

The idea is that the public setFlags() must be called with a "Key", and only friends of Key can create one, as its ctor is private.

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