I’m happy to be corrected as I’ve only really dabbled with Indie game development on and off but my general impression is that the paradigms have gone procedural -> object oriented -> ECS.
For example, Unity is designed around GameObjects but is now adding building out the DOTS framework stack that’s more of a first party ECS system.
Nobody has ever been able to convince me that these informal object systems (eg ECS) aren’t really just OOP with different extensibility mechanisms and/or a different place to stow away object state (oh, and let’s call the objects entities instead).
The only real diversion from objects in games that I’ve seen is the work in Andrew Kennedy’s thesis on FRP for games.
The EC part of ECS is definitely object oriented - more so than mainstream object-oriented systems / languages, in that it favors composition over inheritance (i.e. entities are compositions of components).
But the S in ECS breaks the most fundamental tenet of object-oriented programming - encapsulation of state. And this separation between entities/components and systems is what makes data oriented programming so much cleaner and more powerful than OOP.
If the state is encapsulated somewhere else, why is it no longer OOP? I don’t think Alan Kay would say that having each object simply be a handle into a table of values meant they could no longer be called objects. Heck, if we take the FactoryFactory example as being the bad thing about OOP, and consider that this comes from the GoF design pattern book, there is already a pattern in that book that closely resembles ripping the state out of an object and putting it somewhere else. Again, it is definitely not strawman OOP, but not very many programming systems are, especially modern ones.
Encapsulation in OOP terms means the state is encapsulated with the logic that fetches / mutates it. ECS explicitly is designed to do the opposite. It’s really that simple.
The issue isn’t about how you store the objects but about whether the framework logically encapsulates object data with its associated logic.
> Encapsulation in OOP terms means the state is encapsulated with the logic that fetches / mutates it.
No it doesn't. There are plenty of examples in OO where that isn't true or no physics engine that's been build in the last two decades would work at all. The only core thing needed for OO is that objects have unique identities that then enable a notion of associated state at all. A pure system would not allow for an unbounded number of unique identities at all, you would not really be able to talk about objects at all (or entities or whatever object synonym is preferred).
> There are plenty of examples in OO where that isn't true or no physics engine that's been build in the last two decades would work at all.
It would be surprising if most physics engines were built in an object-oriented way. The only one I'm familiar with, ODE, certainly isn't object-oriented.
> The only core thing needed for OO is that objects have unique identities that then enable a notion of associated state at all. A pure system would not allow for an unbounded number of unique identities at all, you would not really be able to talk about objects at all (or entities or whatever object synonym is preferred).
No, objects in OOP have not just their own unique identities but have their own behavior. Encapsulation is the most fundamental pillar of object-oriented programming. Without that, any procedural C code that makes use of structs could be called object-oriented, since structs would then be synonymous with "objects".
ECS is a type of relational model, it has nothing to do with OO.
EDIT: just to make it clearer, both Simula Style OO and Smalltalk Style OO bundle data and behavior together. The Entity owns the Components and the System.
ECSs are much more like relational databases where an entity is a primary key, components are tables and systems are queries (that also mutate the database). The entity is subservient to the systems, not the other way around.
If somehow a relational database is in any way equivalent to OO then we've reached peak clown world as far as terminology goes.
One of my "ahhh moments" with ECS was when someone pointed out. The ECS has a very 'strict' boundary on DATA(attributes,entities,components) VS
BEHAVIOR (methods,systems,functions).
The 'traditional OOP' usually 'smash/hide/design/encapsulate' these two conflicting powers into one 'Entity'
I think it's 'easier' to write a ball-of-mud in OOP for games, then it is to write ball-of-mud with ECS.
*NOTICE I said 'easier' not 'impossible'
I love the distinctions between BEHAVIOR and DATA, from an organizational point of view. The bigger the whole system is the more value I think a good programmer can get with ECS.
Imagine having to "implement" gravity for 100 different types of 'Objects'. Sure The ECS way would be to have a System(Gravity) that executes the 'same computing' on all entities with a 'MassComponents' and 'PosComponents' for example. The Entity would usually not need to know ANYTHING about Gravity.
Sure the OOP way one can inherit but eventually you inherit yourself into a corner (diamond-problem).
