Explain why Hashmap is used instead of Hashset in unique_impl#623
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bors[bot] merged 1 commit intorust-itertools:masterfrom Jun 7, 2022
Merged
Explain why Hashmap is used instead of Hashset in unique_impl#623bors[bot] merged 1 commit intorust-itertools:masterfrom
bors[bot] merged 1 commit intorust-itertools:masterfrom
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scottmcm
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Jun 7, 2022
src/unique_impl.rs
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| entry.insert(()); | ||
| return Some(elt); | ||
| if !self.iter.used.contains(&v) { | ||
| self.iter.used.insert(v.clone()); |
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Yes, this code is easy to write, but it seems like it also loses the point of why the entry API was used in the first place -- this needs to hash the element twice (once in contains, once in insert), whereas the original code only has to hash it once (in entry).
Given that the HashMap vs HashSet doesn't leak out of the implementation, it seems to me like it's worth a slightly more complex implementation when it can save some hashing work.
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Alright, thanks for the review and your great knowledge.
I'll rework the PR to make the intention clear :)
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Hashmap<V, ()> by HashSet<V>
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bors r+ |
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The
Hashmapwas chosen because of theEntryAPI, but one can work aroundthat easiliy.