[squeak-dev] Object new becomeForward: #normal

Bert Freudenberg bert at freudenbergs.de
Tue Jul 18 14:30:59 UTC 2017

On Tue, Jul 18, 2017 at 4:09 PM, Levente Uzonyi <leves at caesar.elte.hu>

> On Tue, 18 Jul 2017, marcel.taeumel wrote:
> Hi, there.
>> Why are there guards to prevent forward-becoming to immediates (chars,
>> ints)
>> but not to symbols?
> The former is technically impossible due to different object
> representations, the latter is possible and not restricted at all. For
> example, true and false are not immediate objects, you can use #become*: on
> them to blow your image up.
> So, there's no restriction at all if it's technically possible to use
> #become*:.
> The responsibility model is the simplest here: use at your own risk.
> Since this comes up every once in a while, I suggest a comment be added to
> those methods stating the responsibility model explicitly.


*Especially* a warning that becomeForward: does modify the target's hash.

> I don't know how the VM handles immutability in this case, but it's
> possible that it wouldn't let #become*: affect immutable objects.

​I think that would be fine, you should​ be able to become an immutable
object and vice versa.

> On the other hand, I'm sure it would let you change fields of immutable
> objects via #become*:, but that's not an issue in your case.

​This is debatable ...​ I would rather have the VM raise an error when
trying to become a field of an immutable object. Immutable should mean
immutable, no?

​- Bert -​

> Levente
>> This will break your image: "Object new becomeForward: #normal"
>> ... because Cursor class MNU #normal ... :-) Either this is a bug or
>> forward-becoming to symbols is not intended at all.
>> Best,
>> Marcel
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.squeakfoundation.org/pipermail/squeak-dev/attachments/20170718/193bf9d9/attachment.html>

More information about the Squeak-dev mailing list