4 ms·

> My question is, why is that necessary? Exactly what is the benefit, except for a tiny bit of convenience? Why is that better than functions that work on well-

> My question is, why is that necessary? Exactly what is the benefit, except for a tiny bit of convenience? Why is that better than functions that work on well-defined types? The benefit is subtype polymorphism via dynamic dispatch. When values flow through the program they carry the implementations of their operations with them, so a caller can operate on a value without knowing how that operation is implemented; a newly-introduced value can bring a new implementation of an existing operation, and existing callers can use that implementation without knowing that it’s new. There are other ways of achieving this, but OOP is a good one.

dimal 3y ago
I think of subtype polymorphism and dynamic dispatch as two different things, but maybe I'm misunderstanding something here. Subtyping/inheritance is sometimes convenient, but inheritance tends to be a constrictive way to reuse code that increases cognitive load. If B is a subtype of A, now, not only are the data of B coupled to the behavior of A, but the data or behavior of B _may or may not_ be coupled to A depending on whether B overrides A. More coupling. More cognitive load. And if you change A, you have to be careful that you don't break B. Then if you have C that's a subtype of B, then the cognitive load and possibility of unexpected breakage gets even higher. Ugh. No. I'm a simple-minded person. I don't want to think about stuff like that. I see dynamic dispatch simply as a form of delegation, which can easily be accomplished functionally. So, ultimately, again, I see these benefits as being _convenient_ but not _necessary_. And since all design decisions are trade-offs, I look at the downsides of the coupling and find that the trade-offs are simply not worth it.
- tomstuart 3y ago
  I don’t think you’re misunderstanding anything, but to clarify, I’m talking about a more general notion of subtyping (e.g. structural, “duck typing” etc), not necessarily inheritance. Instances of A and B can (in Smalltalk parlance) respond to the same set of messages, and therefore be substitutable for each other, without having any inheritance relationship. In that case there’s no coupling of implementation, only the flexibility of being able to swap out an A instance for a B instance without its collaborators being any the wiser.
- UncleMeat 3y ago
  Subtyping and inheritance are two entirely different concepts. You can have subtyping without inheritance and inheritance without subtyping.

dimal 3y ago

I think of subtype polymorphism and dynamic dispatch as two different things, but maybe I'm misunderstanding something here. Subtyping/inheritance is sometimes convenient, but inheritance tends to be a constrictive way to reuse code that increases cognitive load. If B is a subtype of A, now, not only are the data of B coupled to the behavior of A, but the data or behavior of B _may or may not_ be coupled to A depending on whether B overrides A. More coupling. More cognitive load. And if you change A, you have to be careful that you don't break B. Then if you have C that's a subtype of B, then the cognitive load and possibility of unexpected breakage gets even higher. Ugh. No. I'm a simple-minded person. I don't want to think about stuff like that. I see dynamic dispatch simply as a form of delegation, which can easily be accomplished functionally. So, ultimately, again, I see these benefits as being _convenient_ but not _necessary_. And since all design decisions are trade-offs, I look at the downsides of the coupling and find that the trade-offs are simply not worth it.

tomstuart 3y ago
I don’t think you’re misunderstanding anything, but to clarify, I’m talking about a more general notion of subtyping (e.g. structural, “duck typing” etc), not necessarily inheritance. Instances of A and B can (in Smalltalk parlance) respond to the same set of messages, and therefore be substitutable for each other, without having any inheritance relationship. In that case there’s no coupling of implementation, only the flexibility of being able to swap out an A instance for a B instance without its collaborators being any the wiser.
UncleMeat 3y ago
Subtyping and inheritance are two entirely different concepts. You can have subtyping without inheritance and inheritance without subtyping.