Make HashSet::replace work without raw table internals
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clarfonthey
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Jan 27, 2026
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| /// assert!(std::ptr::eq(replaced, old_key)); | ||
| /// assert!(std::ptr::eq(*entry.key(), new_key)); |
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This seemed like the best way to ensure the key was truly "replaced" instead of having a custom struct with a custom PartialEq implementation.
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Amanieu
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Feb 1, 2026
src/map.rs
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| /// # } | ||
| /// ``` | ||
| #[cfg_attr(feature = "inline-more", inline)] | ||
| pub unsafe fn replace_key(&mut self, key: K) -> K { |
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Since this is an unsafe function, I would prefer if this was called replace_key_unchecked. This explicitly calls out that key equality is not checked and that you are responsible for ensuring this.
This also leaves the door open for a safe replace_key method which has this check.
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In that case, I'll just add that method and have both cases from the start.
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The primary addition here is
OccupiedEntry::replace_key, which allows replacing the key in the map. Since this is an uncommon operation, I decided to make itunsafeand not check for the equivalence of the key, but that can potentially be changed.The other change that is made here is
VacantEntryRef::{insert_with_key,insert_entry_with_key}now haveuncheckedversions which do not check the equivalence of the key, to ensure the same behaviour with thereplacefunction never panicking.Unfortunately, an
UnsafeCellis required to truly make this API work without accessing internals, but it shouldn't ultimately matter, I think. The result is thefind_or_find_insert_indexmethod ofHashMapis no longer exported, and instead the entry API is used byHashSet. Now, the only remaining raw table API forHashSetisRawExtractIf, to be fixed later.