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JuliaServices / AutoHashEquals.jl

A Julia macro to add == and hash() to composite types.
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Include type parameters in hash? #13

Closed omus closed 1 year ago

omus commented 6 years ago

For some types the parametric types (or values) should be included in the hash. Probably @auto_hash_equals should use the typeof a type when producing a hash?

omus commented 6 years ago

For an example see: https://github.com/invenia/Intervals.jl/pull/47

omus commented 6 years ago

(That "close and comment" button is too close to "comment")

matthias314 commented 2 years ago

I think that there is a problem with including type parameters into the hash: It violates the requirement that elements with different hashes must not be considered equal. For example, if you define

@auto_hash_equals struct A{T} x::T end

then isequal(A(0), A(0.0)) is true. Hence the hashes have to agree.

omus commented 2 years ago

isequal(A(0), A(0.0)) is true. Hence the hashes have to agree.

A very good point. I cases where additional information is encoded within the type parameters and those types should not hash to be the same (like in the linked example) declaring a hash method seems like a reasonable approach.

Probably the only thing to be done as part of this issue is to document that @auto_hash_equals isn't a good fit for those scenarios.

gafter commented 1 year ago

This package was completely overhauled in https://github.com/JuliaServices/AutoHashEquals.jl/pull/32. The caller can now decide if type arguments should be considered or not. I made "not" the default for compatibility with existing clients.

Please submit a new issue or PR if you think there is more work to do.