Efficient way of matching entities to systems in an entity component system

Question

I\'m working on a data-oriented entity component system where component types and system signatures are known at compile-time.

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An entity

Answer 1

Depending on the ratio of add/remove of components against signature matching, you can try to build a kind of prefix tree storing references to entities.

The tree itself is static, only leaves which contains entities are runtime built containers.

This way when adding (or removing) a components, you just need to move the reference of the entity to the correct leaf.

When searching for entities matching a signature, you just have to take all the union of the leaves subsuming the signature and iterate over them. And since the tree is (almost) static, you don't even need to search for these leaves.

Another nice point: you bitset can be used to represent the path in the tree so moving an entity is pretty easy.

If the number of components induces an unrealistic number leaves, and not all combination of components are used, you can replace the tree with a hashtable where the bitset is the key and the value is the set of entity references.

That's more algorithmic ideas than concrete stuff, but it seems more reasonable than iterating over the set of entities.