Trait rustc_data_structures::stable_hasher::HashStable

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pub trait HashStable<CTX> {
    fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher);
}
Expand description

Something that implements HashStable<CTX> can be hashed in a way that is stable across multiple compilation sessions.

Note that HashStable imposes rather more strict requirements than usual hash functions:

  • Stable hashes are sometimes used as identifiers. Therefore they must conform to the corresponding PartialEq implementations:

    • x == y implies hash_stable(x) == hash_stable(y), and
    • x != y implies hash_stable(x) != hash_stable(y).

    That second condition is usually not required for hash functions (e.g. Hash). In practice this means that hash_stable must feed any information into the hasher that a PartialEq comparison takes into account. See #49300 for an example where violating this invariant has caused trouble in the past.

  • hash_stable() must be independent of the current compilation session. E.g. they must not hash memory addresses or other things that are “randomly” assigned per compilation session.

  • hash_stable() must be independent of the host architecture. The StableHasher takes care of endianness and isize/usize platform differences.

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