Overriding #= in Graphics and Sounds

> Hi Marcel,
>
>
> I am sending pictures and sounds to a server that only accepts mutually
> different items. However, if multiple of these items are generated using the
> same code, e.g. Morph new imageForm, there is no chance to identify this
> duplicate at the moment.
>
> <http://www.hpi.de/>
>
> Thanks for the hints, this sounds indeed too complex for my use case. For
> now, I decided to simply catch and ignore the server errors about the
> duplicates. It's easier to ask for forgiveness than permission. :-)
>
> Best,
> Christoph
> ________________________________
> Von: Squeak-dev <[hidden email]> im Auftrag
> von Taeumel, Marcel
> Gesendet: Donnerstag, 1. Oktober 2020 14:43:38
> An: squeak-dev
> Betreff: Re: [squeak-dev] Overriding #= in Graphics and Sounds
>
> Hi Christoph.
>
> Hmmm... maybe it is not straightforward to implement? Especially whether
> #class (or #species) should match or not. Reminds me of
> SequenceableCollection >> #= and #hasEqualElements:. I keep on using
> #hasEqualElements: in tests because I don't care about
> Array-vs-OrderedCollection in several places.
>
> [cid:aa12d832-9f5e-4b25-ba80-37b31d0c2dba]
>
> And Form has also a non-trivial hierarchy of variations:
>
> [cid:3ca1fe29-c01e-4821-91ee-d30a841a9712]
>
> For example, would you ignore the #depth if it is black and white anyway?
> Or would you break uses of Dictionaries that are virtually
> IdentityDictionaries because of their current keys and the missing #=?
>
> It can be hard. Maybe it needs to be maintined afterwards. So, YAGNI? :-)
>
> Best,
> Marcel
>
>
> Am 01.10.2020 14:23:37 schrieb Thiede, Christoph
> <[hidden email]>:
>
> Hi all,
>
>
> for a current project, I need to compare form or sound objects with each
> other, but I found out that they do not override #=, so for example, we
> get:
>
>
> (ColorForm extent: 1 @ 1) = (ColorForm extent: 1 @ 1) --> false
>
>
> Wasn't this implemented
>
> a) simply because it looked like YAGNI?
>
> b) for design reasons? For example, should (Form extent: 1 @ 1) be equal to
> (ColorForm extent: 1 @ 1) or not?
>
> c) for performance reasons? I don't know if there any guidelines for
> implement #= (except that you need to implement #hash as well), but is an
> equality comparison generally allowed to be an expensive operation if two
> objects are equal? If two large forms have a different resolution or a
> different bitmap hash, comparison will be fast, but if they are equal, we
> will need to compare every single bit. Would this be okay or a no-go?
>
>
> If implementing #= as proposed is not possible, how would you think about
> implementing it as a keyword message on Form, e.g. #sameAs:?
>
>
> The same questions apply to the AbstractSound hierarchy, too, where I'm not
> sure whether two sounds being played for different duration should equal or
> not.
>
> For a similar discussion, see also this thread: [squeak-dev] FormInspector,
> or also: Text>>#= and its
> consequences<http://forum.world.st/FormInspector-or-also-Text-gt-gt-and-its-consequences-td5121599.html>.
>
> Best,
> Christoph
>