Crate bevy_either[][src]

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This library provides world queries over other world queries, allowing only one of multiple to be satisfied and returning the query items.

Either<T, U>

Given two world queries T and U, Either<T, U> provides a world query that contains either the T’s item or the U’s item. If both T and U successfully match an entity, then only T’s item is given, e.g. there isn’t a “both” variant.

EitherBoth<T, U>

Similarly to Either<T, U>, EitherBoth<T, U> does allow one to match over T’s item or U’s item. What sets it apart is the Both(t, u) variant, allowing both T’s and U’s items to be provided, given that they do both match.


This macro creates a new world query enum with a new variant for each of its possible matched world queries. There isn’t a “both”/“multiple” variant and the priority is always given to the first declared variant when multiple matches occur. This lets you create world queries similar to Either, matching over one of the variant world queries with some priority order.


When using either_many!, you can put readonly before the name of the new query. This will make the resulting type’s fetcher read only. The type is read only if and only if all of its variants are read only, and this is an invariant you must uphold.







A type that contains either the first or second type.


A type that contains either the first type, second type, or both.