派生类派生特征

Question

Here is the diagram:

Class B has some group of methods trait1 . Class B1 and C1 has similar group of methods trait2 . trait2 is derived from trait1 .

How can I implement this? I was going to move all of these trait s methods out from the main hierarchy into some separate one. Then derive B , B1 and C1 from appropriate trait. But then I realized that there would be a problem with inheriting B1 from B because B1 would have trait1 too.

Now I think I can have some field of type, say, TraitBase , and initiate it with appropriate ctor of type either trait1 or trait2 . But I don't like the idea that I should have a field so my class has some special behaviour. May be there is another solution? Thank you.

UPDATE

I mean class B has some feature, which is derived in B1 . C1 should have the feature, which class B1 has.

class B
{
   virtual foo1();
   virtual foo2();


   virtual trait_method1(); //implementation 1
   virtual trait_method2(); //implementation 1
};

class B1 : public B
{
   virtual foo1();
   virtual foo2();


   virtual trait_method1(); //implementation 2
   virtual trait_method2(); //implementation 2
};

class C1 : public C
{
   virtual bar1();
   virtual bar2();


   trait_method1(); //implementation 2
   trait_method2(); //implementation 2
};

Answer 1

Your problem may be solved by virtually inheriting from trait1:

class trait2 : virtual public trait1{} class B : public A, virtual public trait1{} class B1 : public B, public trait2{} class C1 : public C, public trait2{}

However, this design only makes sense if class trait1 is stateless. If not, consider different designs, maybe Bridge pattern.