but if you have the K to compare to, why not just use map[K]V and let the
standard map manage the hash and duplicates - since the OP referred to
hash/maphash I assume they are using keys that are comparable
unless the OP is trying to write a complete custom map implementation - but I
doubt that is the case if they didn’t understand that hashes can have duplicates
> On Jun 25, 2025, at 4:53 PM, 'Axel Wagner' via golang-nuts
> <golang-nuts@googlegroups.com> wrote:
>
> Yes, I meant map[uint64][]struct{K;V}, thanks for correcting me.
>
> On Wed, 25 Jun 2025 at 20:06, robert engels <reng...@ix.netcom.com
> <mailto:reng...@ix.netcom.com>> wrote:
>> That is not correct and will not work - what the op is talking about is if K
>> collides - so this is only a single K - so map[K][]struct{K;V} will only
>> ever have one element in the array…
>>
>>> On Jun 25, 2025, at 12:33 PM, 'Axel Wagner' via golang-nuts
>>> <golang-nuts@googlegroups.com <mailto:golang-nuts@googlegroups.com>> wrote:
>>>
>>> There are ∞ many possible hashable Go values (in particular, all strings)
>>> and 2^64 uint64, so yes, there is a possibility of collision.
>>> How big that risk is depends on how many values you have and what the
>>> damage is, if a collision happens.
>>> Wikipedia has a nifty table:
>>> https://en.wikipedia.org/wiki/Birthday_attack#Mathematics
>>> There, you can see that if you have a 64 bit hash and have, say 190K
>>> elements, the probability of a random collision is roughly 10^-9 (so pretty
>>> small, but not completely impossible).
>>> If a collision is truly problematic, a simple fix would be to use a
>>> map[K][]struct{K;V}. That way, if there *is* a collision on the hash, you
>>> store all the colliding values and can walk the slice to find the right
>>> one. As collisions should be rare, that should be an uncommon cost to pay.
>>>
>>> On Wed, 25 Jun 2025 at 17:26, Pierre Durand <pierredur...@gmail.com
>>> <mailto:pierredur...@gmail.com>> wrote:
>>>> Is it safe to use the result of a hash/maphash (uint64) as a map key.
>>>> Is there a risk of collision ? (different inputs generate the same hash)
>>>>
>>>> Thank you
>>>>
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>>
>
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