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tl;dr: Superclasses make your code brittle. https://en.wikipedia.org/wiki/Fragile_base_class https://en.wikipedia.org/wiki/Fragile_base_class How many people s

by aturek 13y ago

tl;dr: Superclasses make your code brittle. https://en.wikipedia.org/wiki/Fragile_base_class https://en.wikipedia.org/wiki/Fragile_base_class How many people still try to fit their software design into the class hierarchy model? I've been on the composition-not-inheritance side for so long I can't do "traditional OO" justice, but I'd love to hear the counter-arguments in case I'm wrong.

jdlshore 13y ago
No, you're right. "Favor composition over inheritance" has been the go-to OOP design advice for years. The distinguishing feature of OO is modeling concepts by encapsulating state and behavior. For some reason, introductions tend to focus on complex inheritance structures instead. I think that's really unfortunate because it sends entirely the wrong message about OOP. That said, I do occasionally use inheritance for polymorphism and limited code reuse (such as [1]), but I keep it limited in scope, and I don't think I've ever used a multi-level inheritance hierarchy. [1] In my Let's Play TDD screencast series, I use inheritance when modeling a "Dollars" value object. There's a Dollars base class and then various specializations: ValidDollars, InvalidDollars, and UserEnteredDollars. Source code: https://github.com/jamesshore/lets_play_tdd/tree/master/src/com/jamesshore/finances/values https://github.com/jamesshore/lets_play_tdd/tree/master/src/... The screencast: http://www.jamesshore.com/Blog/Lets-Play/ http://www.jamesshore.com/Blog/Lets-Play/
mpweiher 13y ago
Any dependency makes your code brittle. On the other hand, you can't reuse without dependencies. Power/safety tradeoff. Superclasses are just a special case of this.
stonemetal 13y ago
More like Superclasses used incorrectly make your code brittle so don't use superclasses. In so far as I have never found a use case for a class hierarchy 5 deep I agree with him. On the other hand the argument that because you can do it wrong means you shouldn't do it all isn't compelling. I don't think there is a language or language feature that you can't use incorrectly.

by aturek 13y ago

jdlshore 13y ago

No, you're right. "Favor composition over inheritance" has been the go-to OOP design advice for years. The distinguishing feature of OO is modeling concepts by encapsulating state and behavior. For some reason, introductions tend to focus on complex inheritance structures instead. I think that's really unfortunate because it sends entirely the wrong message about OOP. That said, I do occasionally use inheritance for polymorphism and limited code reuse (such as [1]), but I keep it limited in scope, and I don't think I've ever used a multi-level inheritance hierarchy. [1] In my Let's Play TDD screencast series, I use inheritance when modeling a "Dollars" value object. There's a Dollars base class and then various specializations: ValidDollars, InvalidDollars, and UserEnteredDollars. Source code: https://github.com/jamesshore/lets_play_tdd/tree/master/src/com/jamesshore/finances/values https://github.com/jamesshore/lets_play_tdd/tree/master/src/... The screencast: http://www.jamesshore.com/Blog/Lets-Play/ http://www.jamesshore.com/Blog/Lets-Play/

mpweiher 13y ago

Any dependency makes your code brittle. On the other hand, you can't reuse without dependencies. Power/safety tradeoff. Superclasses are just a special case of this.

stonemetal 13y ago

More like Superclasses used incorrectly make your code brittle so don't use superclasses. In so far as I have never found a use case for a class hierarchy 5 deep I agree with him. On the other hand the argument that because you can do it wrong means you shouldn't do it all isn't compelling. I don't think there is a language or language feature that you can't use incorrectly.