[Vm-dev] becomeForward: behavior

Clément Béra bera.clement at gmail.com
Mon Jan 24 07:04:12 UTC 2022

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>

> 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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.squeakfoundation.org/pipermail/vm-dev/attachments/20220124/eca9b21c/attachment.html>

More information about the Vm-dev mailing list