indexmap-rs/indexmap

impl Hash for IndexSet, IndexMap

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alexheretic commented

I think it would be useful for IndexSet, like Vec, to implement Hash. Technically there's no reason IndexMap couldn't either, though I'm not sure how useful it would be practically.

It should be a pretty simple addition, are there downsides?

bluss commented

A hash and equality combination that is consistent needs to be present. I doubt we can or want to do that, because we also want eq rules to be the same as for hashmap(?)

alexheretic commented

Yep it's one or the other. I hadn't thought about wanting equality to disregard order. I'd have expected otherwise but perhaps it's simpler this way.

Thanks for the clarification.

cuviper commented

The open PR rust-lang/rust#48366 is proposing Hash for the standard HashMap and HashSet, using a commutative operation to combine item hashes. Currently that's just wrapping_add, but it sounds like they want to explore stronger options.

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cuviper commented

I've been thinking about reintroducing ordermap as a newtype wrapper that does consider the order for PartialEq and Eq, also adding Hash, PartialOrd, and Ord, and now I've published that:
https://crates.io/crates/ordermap/0.5.0