[Vm-dev] becomeForward: behavior

[Florin Mateoc]

Hi Clément and Marcel,

You are right, other use cases are supported, and there is probably no need
for a separate setIdentityHash: primitive.

I guess I would not have minded if the method currently called
#becomForward: would have been called #becomeForwardCopyHash: (plus a big,
fat comment). As it is, it is not strictly a one way become method, it is a
combination method instead, and its comment does not reflect that.

Best,
Florin


On Mon, Jan 24, 2022 at 3:00 AM Marcel Taeumel <marcel.taeumel at hpi.de>
wrote:

>
> Hi Florin, hi Clément --
>
> yes, that's what Squeak's #becomeForward:copyHash: is for.
>
> See this discussion, where the interference between #becomeForward:, copy
> hash, and ModificationForbidden is explained:
>
> http://lists.squeakfoundation.org/pipermail/squeak-dev/2020-April/208596.html
>
> Best,
> Marcel
>
> Am 24.01.2022 08:04:38 schrieb Clément Béra <bera.clement at gmail.com>:
> Hi Florin,
>
> I believe there are 2 primitives for 2 different use-cases:
> - primitiveArrayBecomeOneWayNoCopyHash 248
> - primitiveArrayBecomeOneWayCopyHash 249
>
> The difference between both is which hash is preserved. I think for your
> use-case you should use the other primitive.
>
> On Mon, Jan 24, 2022 at 5:04 AM Florin Mateoc
> wrote:
>
> >
> > Hi,
> >
> > I am a bit surprised by the #becomeForward: behavior in Squeak. This is
> a
> > one way become, where the target of the operation is the receiver, which
> > sheds its identity/existence. Nobody points to it after the primitive
> > execution, so it is discarded. This understanding also conforms to the
> > method comment.
> > As such, I remember a pattern of usage in VisualAge Smalltalk, where one
> > way become was used as a cheap cleanup/avoidance of memory leaks, by
> doing
> > oneWayBecome: nil. It's not that I advocate for it, but this works in
> > Squeak too, except in Squeak #becomeForward: does an additional thing to
> > the pointers redirection, it changes the identityHash of the argument,
> the
> > non (obvious) target. While I understand this may be useful in certain
> > situations, I think it is a dangerous conflation of activities. A new
> > primitive that sets the identity hash could be used (VA has it)
> explicitly
> > instead when such behavior is desired.
> > As it is, if I do "Object new becomeForward: nil", it succeeds and it
> > changes nil's identityHash.
> >
> > Sorry if this has been debated before,
> >
> > Cheers,
> > Florin
> >
>
>
> --
> Clément Béra
> https://clementbera.github.io/
> https://clementbera.wordpress.com/
> Hi Florin,
>
> I believe there are 2 primitives for 2 different use-cases:
> - primitiveArrayBecomeOneWayNoCopyHash 248
> - primitiveArrayBecomeOneWayCopyHash 249
>
> The difference between both is which hash is preserved. I think for your
> use-case you should use the other primitive.
>
> On Mon, Jan 24, 2022 at 5:04 AM Florin Mateoc <florin.mateoc at gmail.com>
> wrote:
>
>>
>> Hi,
>>
>> I am a bit surprised by the #becomeForward: behavior in Squeak. This is a
>> one way become, where the target of the operation is the receiver, which
>> sheds its identity/existence. Nobody points to it after the primitive
>> execution, so it is discarded. This understanding also conforms to the
>> method comment.
>> As such, I remember a pattern of usage in VisualAge Smalltalk, where one
>> way become was used as a cheap cleanup/avoidance of memory leaks, by doing
>> oneWayBecome: nil. It's not that I advocate for it, but this works in
>> Squeak too, except in Squeak #becomeForward: does an additional thing to
>> the pointers redirection, it changes the identityHash of the argument, the
>> non (obvious) target. While I understand this may be useful in certain
>> situations, I think it is a dangerous conflation of activities. A new
>> primitive that sets the identity hash could be used (VA has it) explicitly
>> instead
>>
>> when such behavior is desired.
>> As it is, if I do "Object new becomeForward: nil", it succeeds and it
>> changes nil's identityHash.
>>
>> Sorry if this has been debated before,
>>
>> Cheers,
>> Florin
>>
>>
>
> --
> Clément Béra
> https://clementbera.github.io/
> https://clementbera.wordpress.com/
>
>
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