C + +: Use compound (composition) instead of private inheritance

Compound methods (composition) and private inheritance can all represent the form of a new class implemented from a class, by using protected members, and by overriding the virtual function.

Choose the compound method preferentially. Reason:

1. The compound method can be implemented to override the virtual function and then prevent the derived class from redefining the virtual function;

2. You can minimize the compilation dependency of a widget by containing only the declarations (comps) of the class and avoiding the header file (inheritance) that contains the base class;

Exception: Private inheritance, which makes Ebo (the most optimized for whitespace base classes), is important in the case of some whitespace base classes, but rarely occurs. So the first compound.

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