Even before I got to the point where I decided I didn't like inheritance, I distinctly recall having conversations about how I felt that using inheritance for anything other than polymorphism didn't usually end up with particularly clean code. I can remember a conversation about this at least as far back as the summer after my freshman year of college, and I don't think I was aware of the idea of "composition" yet, because I remember phrasing my point as something like "inheritance shouldn't be used for 'code-sharing', only for polymorphism".
Out of curiosity, when you say you don't like inheritance, does that mean you never use it at all, or you only use it rarely?
Because even though inheritance often is used in a wrong way, there are definitely cases, where it is the clearest pattern in my opinion.
Like graphic libary things. E.g. everything on the screen is a DisplayObject. Simple Textfields and Images inherit directly from DisplayObject. Layoutcontainers inherit from DisplayObjectContainer which inherits from DisplayObject.
Inheritance here makes a lot of sense to me and I don't see how it could be expressed in a different way without loosing that clarity.
> I don't see how it could be expressed in a different way without loosing that clarity.
What value does the inheritance provide here?
Can't you just use a flat interface per usecase without inheritance and it will work simpler with less mental overhead keeping the hierarchy in mind?
Explicitly your graphic library sounds should be fine to have the interface DisplayObject which you can then add default implementations on. (That's a form of composition)
Inheritance is not necessary, but then very few programming constructs are absolutely necessary. The question is does it help program clarity or not. I think that in some cases, used sparingly, it can. The main danger of inheritance is not that it is OO, but that it is not OO enough. It breaks encapsulation by mixing properties and methods between base classes and derived classes without clear boundaries. Composition is safer because it preserves encapsulation. In general, I think that protected abstract methods are a code smell, because they usually indicate close coupling of details that should be kept separate between the base and derived classes. But used correctly, inheritance can be more succinct and convenient.
To be fair, the compiler generally forces you to keep the forwarding methods updated. It can be irritating, but there's little risk of forgetting in a statically-typed language.
Manual forwarding also operates as a forcing function to write small interfaces and to keep different pieces of logic separated in different layers, both of which feel like good design to me. (Though I'm not saying I'd turn my nose up at a terser notation for method forwarding, haha.)
Even before I got to the point where I decided I didn't like inheritance, I distinctly recall having conversations about how I felt that using inheritance for anything other than polymorphism didn't usually end up with particularly clean code. I can remember a conversation about this at least as far back as the summer after my freshman year of college, and I don't think I was aware of the idea of "composition" yet, because I remember phrasing my point as something like "inheritance shouldn't be used for 'code-sharing', only for polymorphism".
Out of curiosity, when you say you don't like inheritance, does that mean you never use it at all, or you only use it rarely?
Because even though inheritance often is used in a wrong way, there are definitely cases, where it is the clearest pattern in my opinion.
Like graphic libary things. E.g. everything on the screen is a DisplayObject. Simple Textfields and Images inherit directly from DisplayObject. Layoutcontainers inherit from DisplayObjectContainer which inherits from DisplayObject.
Inheritance here makes a lot of sense to me and I don't see how it could be expressed in a different way without loosing that clarity.
> I don't see how it could be expressed in a different way without loosing that clarity.
What value does the inheritance provide here?
Can't you just use a flat interface per usecase without inheritance and it will work simpler with less mental overhead keeping the hierarchy in mind?
Explicitly your graphic library sounds should be fine to have the interface DisplayObject which you can then add default implementations on. (That's a form of composition)
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Inheritance is not necessary, but then very few programming constructs are absolutely necessary. The question is does it help program clarity or not. I think that in some cases, used sparingly, it can. The main danger of inheritance is not that it is OO, but that it is not OO enough. It breaks encapsulation by mixing properties and methods between base classes and derived classes without clear boundaries. Composition is safer because it preserves encapsulation. In general, I think that protected abstract methods are a code smell, because they usually indicate close coupling of details that should be kept separate between the base and derived classes. But used correctly, inheritance can be more succinct and convenient.
Delegation is a very useful part of composition. Almost all OOP languages have two techniques to delegate some methods to another object:
- manually write a bunch of forwarding methods and remember to keep them updated, or
- inheritance.
There’s also automatic delegation like in Kotlin: https://kotlinlang.org/docs/delegation.html
To be fair, the compiler generally forces you to keep the forwarding methods updated. It can be irritating, but there's little risk of forgetting in a statically-typed language.
Manual forwarding also operates as a forcing function to write small interfaces and to keep different pieces of logic separated in different layers, both of which feel like good design to me. (Though I'm not saying I'd turn my nose up at a terser notation for method forwarding, haha.)
...yes? Hence me saying that 'composition' and 'polymorphism' have often been unnecessarily coupled together in 'inheritance'?
Compare: Ruby mixins or Go embedded struct fields.