My advice would be to only use inheritance if your subclass really has an is-a relationship with the parent class.

Can you swap your class in when somebody else is using the parent class? If not, it's not an is-a relationship.

Thinking about classes with Design by Contract in mind often helps. A subclass should:

If this isn't true then inheritance can rapidly become a burden. You end up with a deep class hierarchy where the sub-sub-sub-class does something completely different from original parent class.

Concerns aren't separated in the code, maintenance becomes a nightmare, and you rapidly create a big ball of mud.

I'm not anti-inheritance (hell, I even think multiple inheritance is a good thing :-) but it should only be used for is-a relationships. Anything else is asking for trouble.

In reply to Re: Inheritance vs Delegation: pros and cons by adrianh
in thread Inheritance vs Delegation: pros and cons by bronto

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