[squeak-dev] #= ==> #hash issues

Chris Muller asqueaker at gmail.com
Thu Nov 15 22:20:40 UTC 2018


> Nice.  It seems like we have consensus on what to change.
>
> I'll push these changes (with the tests) to trunk soon.

Hey, "seems" carries enough uncertainty to give us one final look
before trunk.  By "these changes" are you referring to just the
Interval>>#hash or some Array changes, too?  All we've seen so far are
Collections-cbc.810.mcz, could we get one look at your final draft
proposal before trunk?

On a less important note, I personally find a pure conditional
nomenclature more attractive than the embedded ifTrue:ifFalse:, like:

= anObject
    ^ self == anObject or:
        [ (anObject isInterval
            and:
                [ start = anObject first and:
                    [ step = anObject increment and: [ self last =
anObject last ] ] ])
            or: [ super = anObject ] ]

For whatever and whenever you push, I'm sure you already were but,
just in case, I would be grateful if you would please base it solely
off the current top trunk version with no intermediate versions in the
ancestry.   :-)

Thanks a lot finding this and helping get it fixed!

Best Regards,
  Chris

 - Chris


> The fix I have for #hash was exactly what Elliot suggested.
> I'll make sure to include the rehash as well (thanks for the code snippit Bert!)
> If no one objects strenuously, I'll also include Eliot's slight rewrite of #= has well - it is marginally cleaner and equally fast, so now is a reasonable time to include it.
>
> I'll delay working on bug #3380 for now - to fix this, we'd have to also add in a check on class in #= to make sure we aren't comparing an interval to an array.  Unless someone has been bitten by this recently, I'd rather wait.
>
> -cbc
>
>
> On Thu, Nov 15, 2018 at 1:32 PM Chris Muller <asqueaker at gmail.com> wrote:
>>
>> > Isn't this extremely simple to fix?
>> >
>> > #= is implemented in terms of start, step, and last.
>> >
>> > So why not implement #hash as
>> >
>> > ^(start hash bitXor: step hash) bitXor: self last hash
>> >
>> > Then in the postscript do a
>> >
>> > HashedCollection rehashAll
>> >
>> > and that should be it, right?
>> >
>> > I did a quick check using
>> >
>> > Dictionary allInstances select: [ :dict | dict keys anySatisfy: #isInterval]
>> >
>> > and the system seems fine after that.
>>
>> You forgot about the universe that lies beyond the fringes of the
>> image.  There be persistent data files out there.  And users.
>> Possibly with systems that rely on Interval>>#hash.
>>
>> But since most applications don't use non-Integer based Intervals
>> (since Interval doesn't really support them, by design, I guess),
>> there's no reason whatsoever to decimate the universe when Eliot's
>> simply fixes the corner case that no one is using anyway.
>>
>> +1 to Eliots suggestion to fix Interval>>#hash.
>>
>>  - Chris
>>
>


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