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by hota_mazi 3094 days ago
> In practice inheritance is a very special case of composition that is only advantageous in a very narrow set of usecases.

You are confused. See my other message below where I show that composition and inheritance are not mutually exclusive (and arguably, the best of both worlds is using inheritance via composition).
1 comments
mikekchar 3093 days ago
Edit: Sigh... This message is badly written, mainly because I confused your point :-) I'm not quite sure why I was thinking you were arguing that it was not an ISA relationship. In any case, removing my addled brain from the equation is probably useful -- you can probably figure out that there is more than one way to look at this. And while you clearly think that your way is correct, it is useful to view it from other perspectives.

While it is interesting to see your viewpoint, you may also consider that not everybody will see it the same way that you do. For example, why do you suppose that inheritance via composition makes it not an ISA relationship? Is a Swiss Army knife a screwdriver? You may say "no", but others may say "yes" -- it is a screwdriver by way of containing a screwdriver. You can verify this usage of the language simply by listening to sales pitches for the crap they sell on the shopping channel :-) ISA and HASA do not necessarily need to be exclusive properties.

It's easy to get wrapped up in your own definitions of things and to block out how others may view the universe. This is precisely why I originally asked the question. I appreciated the enlightenment. I hope that the above will help you achieve the same.

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hota_mazi 3092 days ago
> For example, why do you suppose that inheritance via composition makes it not an ISA relationship?

I don't. My other message [1] clearly states:

    class A(b: B) : B by b // IS_A via composition
My point is that inheritance can be achieved in many different ways, composition being one of them.

Inheritance is an architecture concept, composition is a mechanism which can be used to implement inheritance. They are complementary.

[1] https://news.ycombinator.com/item?id=16050458

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