Classical Inheritance Divergence

Question

I'm wondering what should be done in the case of needing Roles or Traits but in a classical inheritance environment. I have stemming of a class down two roads, both of which stem from a root class, however, I want to link the diverged classes on the two roads together to share the same functionality. See below:

+-- Base
 +-- Base_Processor
 | +-- Base_Processor_Request
 |  +-- Base_Processor_Request_Ajax
 +-- Base_Impl
  +-- Base_Impl_MyImpl
   +-- Base_Impl_MyImpl_Processor (extends from Base_Processor)
    +-- Base_Impl_MyImpl_Processor_Request (extends from ??)
     +-- Base_Impl_MyImpl_Processor_Request_Ajax (extends from ??)

What would be the best way to link Base_Impl_MyImpl_Processor_Request and Base_Processor_Request together while still extending from Base_Impl_MyImpl_Processor, and also link Base_Impl_MyImpl_Processor_Request_Ajax in the same fashion.

Thanks in advanced.

Prefer Composition Over Inheritance. – Alex Burtsev Apr 11 '12 at 18:40 — Alex Burtsev, Apr 11 '12 at 18:40

score 2 · Accepted Answer · edited May 23 '17 at 12:04

2

I agree 100% with Alex Burtsev's comment - that many levels of inheritance looks like a dependency nightmare (and, as you're discovering, rather difficult to reuse particular bits of code across classes when you use inheritance that much).

Typically I wouldn't expect trait classes to be plugged into a heirarchy - to my mind, traits are standalone concepts which define variations across implementation details, and therefore only belong to an interface rather than being derived from a base class

If this is existing code and you have multiple elements which you need to reuse among different derived classes, I think it would make more sense to split those out to separate classes which are not related to your heirarchy at all.

It would seem that Processor, Request and Ajax could better serve you as separate entities.

edited May 23 '17 at 12:04

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answered Apr 11 '12 at 21:48

Ben Cottrell

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So, correct me if I'm wrong, but you're saying I should make those into interfaces, and not reuse code across Base and Impl, correct? But they will both implement the same interfaces. Thanks for your response, by the way! – Kyle Apr 12 '12 at 02:52
Nevermind. Figured out what you mean [Composition versus Inheritance](http://www.artima.com/designtechniques/compoinh.html) Thanks! – Kyle Apr 12 '12 at 03:00

Classical Inheritance Divergence

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