feat(engine): Entity id versioning #11
Description
Reserve some entity id bits for versioning. An entity reference will mask these bits to check whether the entity is 'alive', while inside the engine the same underlying id is reused.
Flecs uses 16 bits that would otherwise be masked by relations for a version id. Notably, this means for versioning to work correctly any relations referencing this entity should be removed when it its removed (to avoid needing to store entity version on relations).
Resources
- Mention in flecs blog: https://ajmmertens.medium.com/doing-a-lot-with-a-little-ecs-identifiers-25a72bd2647
- ECS back and forth blog: https://skypjack.github.io/2019-05-06-ecs-baf-part-3/