ECS changes the way you access and mutate the world, compared to classic data graph / reference tree, more classic pervasive singletons ("managers"), or even mo

ECS changes the way you access and mutate the world, compared to classic data graph / reference tree, more classic pervasive singletons ("managers"), or even more classic straight global variables. But in ECS engines you still access a portion of global world state you're interested in, and you mutate some portion of it. The ability to declare what those portions are, when present, allows ECS engines to do stuff like parallel execution of systems, and it also prevents a host of data races, but imho there's nothing really functional / pure / immutable about it.