In a tight loop (50-100ns/cycle) I am using a dict filled with randomly generated UInt64 keys. I think that they could be used directly in a hashmap, without hashing, so I am looking for a hashmap with a custom (here the identity) hash function. I hope to gain 2.5ns per cycle: julia> @btime hash(…

[image] tisztamo: I was not able to quickly find a package that allows that. Is there any? Just wrap your keys in a new type: struct MyKey val::UInt end Base.hash(a::MyKey, h::UInt) = xor(a.val, h) Base.(==)(a::MyKey, b::MyKey) = a.val == b.val

It takes only a patch of few lines to allow Base’s Dict to handle that, here is a POC , where you’re welcome to comment :slight_smile: I don’t know of an package doing that, but if this PR isn’t merged soon enough, I will package it up.

Thanks, it would be great to have that in Base!

Thank you, it works! I mistakenly thought this will have a performance impact, that’s why I asked for a solution here, but now I have learned to better embrace immutable structs!

There’s a reason one of Julia’s unofficial mottos is “don’t pay for what you use”

I am sorry. This is missing a lot of steps for me: How would the dict be defined? mydict = Dict{MyKey, String}() akey = MyKey(10) mydict[akey] = "foo" This seems restrictive. Key values need to be integers to convert to UInt. It’s actually slower than a normal dictionary. I am looking for a sim…

Dictionary with custom hash function

General Usage

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Dictionary with custom hash function

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