C.137: Use virtual bases to avoid overly general base classes
C.137: 使用虚基类避免过于一般的基类
Reason(原因）
Allow separation of shared data and interface. To avoid all shared data to being put into an ultimate base class.
允许共享数据和接口的分离。避免将所有的共享数据放进一个终极基类中。
Example(示例）
<code>structInterface{
virtualvoidf();
virtualintg();
//...nodatahere...
};
classUtility{//withdata
voidutility1();
virtualvoidutility2();//customizationpoint
public:
intx;
inty;
};
classDerive1:publicInterface,virtualprotectedUtility{
//overrideInterfacefunctions
//MaybeoverrideUtilityvirtualfunctions
//...
};
classDerive2:publicInterface,virtualprotectedUtility{
//overrideInterfacefunctions
//MaybeoverrideUtilityvirtualfunctions
//...
};/<code>Factoring out Utility makes sense if many derived classes share significant "implementation details."
如果很多派生类之间分享特别有用的共通的"实现细节"，从中分离出共通功能就是有意义的。
Note(注意)
Obviously, the example is too "theoretical", but it is hard to find a small realistic example. Interface is the root of an interface hierarchy and Utility is the root of an implementation hierarchy. Here is a slightly more realistic example with an explanation.
很显然，示例过于理论化了，但是找到一个接近现实的小例子太难了。接口是接口体系的起点，而公用程序是实现体系的起点。这里有一个带有说明的，略微更接近实际的例子。
链接：https://www.quora.com/What-are-the-uses-and-advantages-of-virtual-base-class-in-C%2B%2B/answer/Lance-Diduck
Note(注意）
Often, linearization of a hierarchy is a better solution.
通常，线性的继承体系是较好的解决方案。
Enforcement(实施建议)
Flag mixed interface and implementation hierarchies.
提示接口继承和实现继承体系混合的情况。
原文链接
https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#c137-use-virtual-bases-to-avoid-overly-general-base-classes
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