Add empty and stacked indexes #346
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Draft for now, because of the 3.2.0 target. Other than that, this should be ready. |
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| * | ||
| * @since 3.2.0 | ||
| */ | ||
| public final class EmptyIndex implements IndexView { |
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Ehm, what is this for? I mean it's not even used internally, is it? And what's the benefit of this optimized empty version? Right now, there are other ways to obtain an empty index such as Index.of(Collections.emptyList()). Shouldn't we use the EmptyIndex in similar scenarios? Maybe we should add something like Index.empty()?
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So there's a difference between empty Index (which is fairly heavy-weight) and empty IndexView (which is super light-weight).
I don't have a use case for it myself, but apparently Hibernate Search people do: https://github.com/hibernate/hibernate-search/blob/main/util/common/src/main/java/org/hibernate/search/util/common/jar/impl/JandexUtils.java#L51 And it feels right to have a dedicated implementation directly in Jandex.
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If so, then we should probably promote the API a bit more, i.e. mention/link it in the IndexView, maybe even add IndexView.empty() etc.
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I did contemplate about a public static IndexView empty() method on IndexView vs. a public class EmptyIndex and didn't feel strongly about either. I can switch to the static method for sure.
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Added IndexView.empty().
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I think that it's ok to have both.
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Yeah, agree, I didn't know why I didn't make EmptyIndex.INSTANCE public. Fixed.
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| * Creates a stacked index from given {@code indexes}. The first element of the list is the bottom-most index |
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This means that when you build the stack you need to add the indexes with "lower priority" first which is IMO not exactly intuitive and practical. I wonder if we should offer some more flexible way of building the stack.
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I actually had a push(IndexView) method implemented (that would return a new stacked index with the given argument on top of the stack), but I felt like a solution in search of a problem, so I ultimately removed it. It should be easy to re-add.
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Added StackedIndex.pushIndex().
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A stacked index is a composition of multiple indices with overlay semantics. Overlaying is done on class granularity. When the composition doesn't contain duplicate classes (multiple classes with the same name), a `StackedIndex` behaves just like a `CompositeIndex`, but when duplicates appear, the behavior of `StackedIndex` is actually well defined. This commit also adds a test for index navigation methods from `IndexView`, as those have not been tested at all. Some tests reveal inconsistencies in how `CompositeIndex` behaves in presence of duplicates, which is not nice, but this commit intentionally doesn't modify `CompositeIndex` behavior.
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Fixes #142