C.137: Use virtual bases to avoid overly general base classes
C.137: 使用虛基類避免過於一般的基類
Reason(原因）
Allow separation of shared data and interface. To avoid all shared data to being put into an ultimate base class.
允許共享數據和接口的分離。避免將所有的共享數據放進一個終極基類中。
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."
如果很多派生類之間分享特別有用的共通的"實現細節"，從中分離出共通功能就是有意義的。
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.
很顯然，示例過於理論化了，但是找到一個接近現實的小例子太難了。接口是接口體系的起點，而公用程序是實現體系的起點。這裡有一個帶有說明的，略微更接近實際的例子。
鏈接：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，線性的繼承體系是較好的解決方案。
Enforcement(實施建議)
Flag mixed interface and implementation hierarchies.
提示接口繼承和實現繼承體系混合的情況。
原文鏈接
https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#c137-use-virtual-bases-to-avoid-overly-general-base-classes
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