Allow alternative hash functions in GraphMap#622
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ABorgna merged 1 commit intopetgraph:masterfrom Apr 1, 2024
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cuviper
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May 11, 2024
| pub fn new() -> Self | ||
| where | ||
| S: Default, | ||
| { |
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FYI: by leaving S open here, it means that type inference can't figure it out, and it won't use the default either. e.g. This used to work:
let mut graph = GraphMap::new();
// ... other code that insert stuff, inferring those types but *not* the hasherNow to allow inference I have to write:
let mut graph = GraphMap::<_, _, _>::new(); // now 4th param `S` is defaultedThat's why HashMap::new() and IndexMap::new() only use the default hasher, while default() is fully generic.
See also: https://faultlore.com/blah/defaults-affect-inference/
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Don't get me wrong, this is a great feature overall! I would have just left new() on the old hasher for the reason above, but it would be a breaking change to go back on that now.
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Ack, thanks for the comment. I would have done it differently if I'd realized.
This was referenced Jun 25, 2025
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Hi there @bluss and @ABorgna!
Today,
GraphMapusesIndexMap's default choice of hash function. Like many Rustaceans, I have a use case that is bottlenecked by hashing, which could take advantage of a faster hash function.This change allows users of this crate to pick alternative hashers, as they might with an
IndexMapor aHashMap, but only if they want to. Existing code will still work, because eachimplhas been made more generic, sincestd::hash::RandomStatealready implementsBuildHasherandDefault.I took
dev-dependenciesonahashandfxhash, and extended a benchmark I'd previously contributed: