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Entity systems still rely on inheritance as you typically have an Entity baseclass that all entities derive from. That's just a single level of inheritance. Uni

Entity systems still rely on inheritance as you typically have an Entity baseclass that all entities derive from. That's just a single level of inheritance. Unity does this through MonoBehavior. Unreal is more inheritance-heavy but developers typically subclass something like `Actor` to one level of additional inheritance beyond the Engine's subclasses. A lot of engines will have multiple superclasses behind a Entity class, but that's an implementation detail of the engine itself and to the game developer, it's treated as a single base class that is typically subclassed a single time for the entity itself. Even in ECS's you will often find inheritance. Some implementations have you inherit a Component struct, others will have the systems inherit a System class. I'm sure it's still used today in some engines and by some developers but the overwhelming opinion is that doing something like Entity -> Actor -> Monster -> Orc -> IceOrc is a bad idea. Instead it would be like class IceOrc : Entity { components {Health, Enemy, PlayerSeek, Position, etc} } Where each component is like class Health : Component { value = 100 } And yeah, they favour composition re. Components, it's just that the components tend to inherit from a Component class. But I would still call it composition!

flohofwoe 9mo ago
Yes there is some inheritance left in those composition-systems, but a single inheritance level is really more like implementing an interface.
- llmslave2 9mo ago
  It is, but you get the benefit of shared behaviour and state. Like an Entity might have a Position, a reference to the World, the Screen, methods for interacting with other entities, etc. You don't get that from simply implementing an interface, although it's not difficult to pass those into the object. A common example I've seen is having every class extend an EventEmitter superclass. You could implement that as part of the interface but that becomes a ton of duplication. I think of it like this: If you model your domain as something like `A : B : C : D {}` you get all the problems of inheritance, when simply doing D { A; B; C; } gives you the same benefits without the problems. Doing `A : X {}, B : X {}, C : X {}` sidesteps most of the problems with inheritance but gives you some of the benefits as well.

flohofwoe 9mo ago

Yes there is some inheritance left in those composition-systems, but a single inheritance level is really more like implementing an interface.

llmslave2 9mo ago
It is, but you get the benefit of shared behaviour and state. Like an Entity might have a Position, a reference to the World, the Screen, methods for interacting with other entities, etc. You don't get that from simply implementing an interface, although it's not difficult to pass those into the object. A common example I've seen is having every class extend an EventEmitter superclass. You could implement that as part of the interface but that becomes a ton of duplication. I think of it like this: If you model your domain as something like `A : B : C : D {}` you get all the problems of inheritance, when simply doing D { A; B; C; } gives you the same benefits without the problems. Doing `A : X {}, B : X {}, C : X {}` sidesteps most of the problems with inheritance but gives you some of the benefits as well.