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If Inheritance is so bad, why does everyone use it?

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Re: If Inheritance is so bad, why does everyone use it?

#281

Post by mattnewport »

lewispollard wrote: post #12
mattnewport wrote: post #9

Earlier quoted context omitted.

Inheritance doesn't work well for games, that's why so many games take a component based approach like Unity, or full blown ECS.

Well, it does work well for the engine part of game engines, and graphics related code in particular as the GP says - it's just gameplay code where OO falls a bit flat.

Not really, the data oriented design movement in games programming that eschews OOP is driven by performance concerns of traditional OOP code on areas like rendering.

As a graphics programmer for many years I can also say that OOP is not really a good fit design wise for modern rendering engines, it mostly just gets in the way.

Re: If Inheritance is so bad, why does everyone use it?

#282

Post by Sankozi »

captainmuon wrote: post #39

I feel people don't understand what inheritance and (object orientation in general) is useful for, misuse it, and then it gets a bad reputation. It's not about making nice hierarchies of Cars, Fruits, and Ovals. For me the main point is (runtime) polymorphism. E.g. you have a function that takes a general type, and you can pass multiple specific types and it will do the right thing. And if you want to avoid huge if-e…

You can have polymorphism without inheritance and inheritance without polymorphism. The big problem with inheritance is that it is really tricky to write those base classes. Making class inheritable by default in programming language is often considered a big mistake, because only carefully designed and documented class can be safely extended.

Re: If Inheritance is so bad, why does everyone use it?

#283

Post by mattnewport »

professoretc wrote: post #81
mattnewport wrote: post #9

Earlier quoted context omitted.

Inheritance doesn't work well for games, that's why so many games take a component based approach like Unity, or full blown ECS.

The implementation of inheritance (more specifically, polymorphism and dynamic dispatch via vtables) is a problem in games, because it adds an extra layer of indirection, and screws with cache locality. But the semantics of inheritance ( X ISA Y ) still apply. In an ECS, the implementation is different (struct-of-arrays) but you can still think of an entity as "inheriting from" the various components its built from.

That's not really accurate. Component based systems are designed specifically to address situations that traditional inheritance doesn't handle well.

Examples are usually something like having a base entity, a player that inherits from entity and an enemy that inherits from entity. Then you have a magic user and a barbarian inherit from enemy but now you also want your player to be able to use magic. Traditional OOP doesn't make it easy to share the implementation.

Even with composition and interfaces you still have problems with most traditional OOP languages when you want to do things like change the set of components of an entity dynamically at runtime (player gains or loses the ability to use magic during the game).

"Is a" is often not the relationship you want to model. A player and an NPC both have the "has a" relationship to an inventory, not the "is a" for example.

Re: If Inheritance is so bad, why does everyone use it?

#284

Post by gpderetta »

bsder wrote: post #218
caseysoftware wrote: post #156

The key is "prefer composition to inheritance" and dates back to Gang of Four. The word "prefer" is critical to understand. It just means "usually choose A over B" not "B is never the right answer." Unfortunately, since we - as an industry - like hard and fast rules, we move towards that second explanation and act like inheritance never makes sense. Like any tool, there's a time and place where it is the best tool, o…

Inheritance was a premature optimization for computers with small memory. It did its job. However, once memory got big, people forgot to throw it out. Composition uses a lot more indirection. That's bad on modern CPUs. Pointer chasing throws out performance, so composition is not always preferred, either.

Composition doesn't imply pointer chasing.

In C++ there is extremely little difference between the code granted for inheritance or composition (unless you use virtual inheritance), so I have no idea what overhead you are talking about.

Re: If Inheritance is so bad, why does everyone use it?

#285

Post by gpderetta »

layer8 wrote: post #189
VirusNewbie wrote: post #175

Earlier quoted context omitted.

>You can’t build a dynamic list of objects implementing the same interface in different ways with parametric polymorphism. Yes you can. that's the whole point of type classes.

Not without runtime polymorphism. Parametric polymorphism does not imply nor by itself implement runtime polymorphism. I.e. C++ templates, or generics in other languages, provide parametric polymorphism, but not runtime polymorphism.

Universal Vs existential qualification.

For example in c++ std::function exhibits parametric polymorphism without templates.

Re: If Inheritance is so bad, why does everyone use it?

#286

Post by sfn42 »

cornstalks wrote: post #203
kaba0 wrote: post #177

Earlier quoted context omitted.

> The runtime part is what I dislike. If I have a fruit which is an apple or a banana, I can't pass that to a method expecting an apple or banana. It can only be passed as a fruit. Heh? An apple is a fruit, you can pass it to any place expecting the former. Like, this is Liskov’s substitution’s one half. With generics, you can be even more specific (co/in/contra-variance).

I think GP is talking about something like this: Fruit* fruit = new Apple(); ConsumeApple(fruit); // Doesn't work; requires Apple* fruit = new Banana(); ConsumeBanana(fruit); // Doesn't work; requires Banana* ConsumeFruit(fruit); // Okay, function signature is void(Fruit*)

But why would you want to be able to pass an apple to a function expecting a banana? Doesn't even make sense, the whole point is that the type system forces you to consider this stuff.

If OP wanted to be allowed to do whatever and just have the software fail at runtime, JS is right there.

Re: If Inheritance is so bad, why does everyone use it?

#287

Post by jonathanstrange »

mrkeen wrote: post #75
jonathanstrange wrote: post #72

I prefer languages with full OOP, ideally with multiple dynamic dispatch. What I'm not fond of are languages like Java that overuse OOP design patterns, force you into them, or require lots of OOP boilerplate. If you have a class whose sole instance serves as a factory for other objects, you know you're on the wrong path. But I've never seen any coherent and sound arguments against OOP in general. Nobody forces you t…

> But I've never seen any coherent and sound arguments against OOP in general. How about arguments for OOP? Especially for things which can't be done better elsewhere.

As others have said, GUIs are the place where OOP shines. There are no things OOP does that can't be done elsewhere, what happens in practice is that programmers invent their own ad hoc object systems and start programming in an object-passing style (see e.g. Gtk).

Re: If Inheritance is so bad, why does everyone use it?

#288

Post by EVa5I7bHFq9mnYK »

eddd-ddde wrote: post #104
captainmuon wrote: post #39

I feel people don't understand what inheritance and (object orientation in general) is useful for, misuse it, and then it gets a bad reputation. It's not about making nice hierarchies of Cars, Fruits, and Ovals. For me the main point is (runtime) polymorphism. E.g. you have a function that takes a general type, and you can pass multiple specific types and it will do the right thing. And if you want to avoid huge if-e…

Except inheritance is the premature optimisation of interfaces. Inheritance forces you to define the world in terms of strict tree hierarchies, which is very easy to get wrong. You may even do a great job today, but tomorrow such properties don't hold anymore. Regular composition allows the same functionality without making such strong assumptions on the data you are modelling.

True. Modelling the world as a tree oversimplifies it, as there are also lateral and even backwards dependencies, and at a sufficiently complex level abstractions start to leak all over, making it a mess. But at some low to medium level of complexity it might work.

Re: If Inheritance is so bad, why does everyone use it?

#289

Post by EVa5I7bHFq9mnYK »

poisonborz wrote: post #77

My take is that after something becomes sufficiently popular and mainstream, for a lot of people who want to be seen as innovative, the only way is to lash out against it. See all the articles on how hellishly bad agile, php or javascript is. A lot of criticism is valid of course, but that is irrelevant in the larger scheme of things - there is a reason they became what they are today.

There is a lot of things in the world today that are very bad and very popular, not the reason to stop hating them.

Re: If Inheritance is so bad, why does everyone use it?

#290

Post by pointlessone »

seanwilson wrote: post #84

Nobody calls it this, but cascading styles in CSS is just like inheritance and I think should be avoided for all the same reasons. I feel it's a big part of why CSS at scale becomes unmaintainable. There isn't even a built-in way to compose two classes together if you want to avoid cascading/inheritance. It looks like composition over inheritance has caught on as the better default in other languages, but in the CSS…

It's because people don't understand cascade we end up with pages that have text in 18 different font sizes. Cascade was a brilliantly simple idea and gave great consistency of design easily. At the time it was great. I believe the only reason most people are mad at CSS is because specificity is hard to grasp and order-dependent resolution and you don't control it when you bundle 500 packages. You get scores of megabytes of CSS that can randomly change order. Since then we've got more tools to control cascade: layers, scopes, inherit/initial/revert/revert-layer/unset for every property, etc. But people still insist on inline styling. I get it, it's much simpler. But they will keep being unhappy until they learn cascade and stop fighting tools. Yes, learning takes effort but so does resistance.
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