Relax constraint in hash_map::EntryRef insertion methods K: From<&Q> to &Q: Into<K> #611
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…to &Q: Into<K> Currently `EntryRef::or_insert*` methods have constraint `K: From<&Q>` which is required to construct "owned" key from "borrowed" key during insertion operation. Rust documentation recommends not to use `From` as trait constraint, and instead prefer to use reversed `Into` trait constraint: https://doc.rust-lang.org/std/convert/trait.From.html > Prefer using Into over using From when specifying trait bounds on a generic > function. This way, types that directly implement Into can be used as arguments as well. Changing constraint `K: From<&Q>` to `&Q: Into<K>` extends support of insert operation to additional cases where `K` does not implement trait `From<&Q>`, but `&Q` does implement trait `Into<K>`. **API compatibility**: `&Q: Into<K>` is a strict superset of `K: From<&Q>` (because of blanket implementation https://doc.rust-lang.org/std/convert/trait.Into.html#impl-Into%3CU%3E-for-T), so this change does not break existing hashbrown API compatibility; all existing code will work with new trait constraints.
Amanieu
approved these changes
Apr 5, 2025
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Currently
EntryRef::or_insert*methods have constraintK: From<&Q>which is required to construct "owned" key from "borrowed" key during insertion operation.Rust documentation recommends not to use
Fromas trait constraint, and instead prefer to use reversedIntotrait constraint:https://doc.rust-lang.org/std/convert/trait.From.html
Changing constraint
K: From<&Q>to&Q: Into<K>extends support of insert operation to additional cases whereKdoes not implement traitFrom<&Q>, but&Qdoes implement traitInto<K>.API compatibility:
&Q: Into<K>is a strict superset ofK: From<&Q>(because of blanket implementation https://doc.rust-lang.org/std/convert/trait.Into.html#impl-Into%3CU%3E-for-T), so this change does not break existing hashbrown API compatibility; all existing code will work with new trait constraints.