EntityIndex¶
EntityIndex is a transient counterpart to EntityHandle that identifies an entity by its buffer position within a group. It is only valid until the next entity submission — any add, remove, or tag change that touches the entity's group can shift buffer positions, invalidating the index.
In exchange, it skips the handle-to-index resolution that EntityHandle does internally. That resolution is nearly free — it's a single index into a flat array (the handle's id selects the entry directly), not a hash-map lookup or a pointer chase. So EntityIndex saves almost nothing while exposing you to a real invalidation hazard.
Prefer EntityHandle in almost all cases. Reach for EntityIndex only when profiling points at that resolution inside a tight inner loop — where you've already resolved a handle and perform several operations on the same entity within a single submission.
Every entity-targeted method on EntityHandle has a matching overload on EntityIndex:
// Inside a system, `World` is the system's WorldAccessor.
EntityIndex idx = handle.ToIndex(World);
idx.SetTag<BallTags.Resting>(World);
idx.Component<Position>(World).Write = newPos;
The methods accept either a WorldAccessor (main thread) or a NativeWorldAccessor (jobs).
To convert back to a stable handle when you need to cross a submission boundary: