insert_unique_unchecked operation#293
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bors merged 2 commits intorust-lang:masterfrom Sep 13, 2021
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Sometimes a map is constructed when it is known that all keys are unique (e. e. if keys are coming from another map or from a sorted/deduplicated iterator). In this case we can make insertion faster by skipping a check that a key already exists in the map. `insert_unique_unchecked` is guaranteed to be memory-safe, but does not guarantee anything beyond that: if inserted key is not unique, `HashMap` can panic, loop forever, return incorrect entry etc. Added simple benchmark. `insert_unique_unchecked` is about 30% faster than `insert`. Your mileage may vary of course. Similar PR was [added to `indexmap` crate](indexmap-rs/indexmap#200) and they asked to discuss the name of the operation with `hashbrown` crate owners to come to the same naming convention (if `hashbrown` is willing to have the same operation).
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Could you change this to return an |
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Regular What would be the use case for that reference? If a user need to modify an entry, they can do that before the insertion. I can do it of course, just want to understand it. |
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... we can't return |
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Added a commit on top which changes to return |
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@bors r+ |
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📌 Commit 7002f9f has been approved by |
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☀️ Test successful - checks-actions |
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Sometimes a map is constructed when it is known that all keys are
unique (e. e. if keys are coming from another map or from a
sorted/deduplicated iterator). In this case we can make insertion
faster by skipping a check that a key already exists in the map.
insert_unique_uncheckedis guaranteed to be memory-safe, but doesnot guarantee anything beyond that: if inserted key is not unique,
HashMapcan panic, loop forever, return incorrect entry etc.Added simple benchmark.
insert_unique_uncheckedis about 30%faster than
insert. Your mileage may vary of course.Similar PR was
added to
indexmapcrateand they asked to discuss the name of the operation with
hashbrowncrate owners to come to the same naming convention (if
hashbrownis willing to have the same operation).