How to query a entity by a component value, not component type? about shipyard

[leudz]

This is a broad question and there are a lot of answers based on each specific case.

is_in_acid for example could be handled using a spacial data-structure.
Or using only shipyard you could check only entities that moved and tag/untag them.
But most likely this isn't an issue to begin with. If you look here you'll see that iterating 2 storages with 10k entities takes 25us. This will vary based on the hardware but it's a tiny number.
The ECS is usually not the bottleneck.

For the general question "How to query a entity by a component value" you could use custom views to build and update an index like discussed here for bevy.
But it would be pretty complicated and I don't know what the actual performance would look like.