What hash function / algorithm does #[derive(Hash)] use by default?
This definitely correctly answers the question I asked. I intended to ask a different question (but still not sure how to formulate it). The write_u8, write_u16, ... functions calls the write function of DefaultHasher in std::collections::hash_map - Rust , which appears to be using SipHasher in std::hash - Rust ?
I completely agree with @cuviper 's point that the hash function depends on the impl of the trait. I think what I should have asked is what is used to hash
Is the answer for
&[u8] siphash-2-4 ( https://crates.io/crates/siphasher ) ? Or is it now using something else ?
There are multiple generic levels involved here.
Hash for &T(like
&[u8]) simply forwards to the inner type.
Hash for [T](like
<Hash for T>::hash_slice.
<Hash for u8>::hash_slicecalls
Hasher::writefor the entire slice.
For the actual
Hasher, yes the default for
HashMap is currently a sip-hash, although you can choose something else with the
S type parameter. The implementation of that default hasher is internal to the standard library, not using the crate you mentioned.
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