> the ECS equivalent of "your language doesn't have multimethods" problem in OOP ... you solve that by creating a Component composing other Components.

I'm not sure about having solved that, but yes, a component may check its entity for other components to inspect and/or modify, even add/remove components from its entity, or add/remove entire entities from the scene (like a ShootingComponent asking a PhysicsComponent to simulate recoil, and spawning bullet entities.)

If a dependency is missing, a component alters or omits parts of its behavior or silently skips its frame update.

I'd really like to try the SwiftUI idiom in games, where the code is a declarative description of a scene, that an engine can take to construct the actual scene using whatever architecture it wants under the hood.

I also wonder how far you could take SwiftUI itself for making games without using any other framework.