[squeak-dev] sends of #class and #== considered harmful, may we please stop?

Levente Uzonyi leves at caesar.elte.hu
Thu Nov 22 22:51:53 UTC 2018

Hi Chris,

I think it should work the other way around. When you want to be able to 
use proxies everywhere (which can't work btw, because everywhere is just 
too vague), there should be a switch - a preference with an action - that 
recompiles all methods with the #== and #class bytescodes disabled except 
for those methods which have a special pragma preventing such 

I'm surprised you didn't mention other special methods like #ifTrue:, 
#whileTrue:, #repeat:, #to:do:, etc. I think that's because you rarely 
create proxies for numbers, booleans and blocks.


P.S.: Please don't use #species for such thing. Why? #species is supposed 
to return "the preferred class for reconstructing the receiver". It is not 
a substitute for #class.

On Thu, 22 Nov 2018, Chris Muller wrote:

> Hi guys,
> Something I've been wanting to ask the community for years, but never
> had the gumption, was about changing how we write our #= and #hash
> methods, but now that we're combing through them anyway, I must!
> Basically, it comes down to Proxy's.  I want them to work better in
> Squeak.  But every time we put another send to #class or #== in an
> implementation of #=, since those methods are inlined, they're too
> brittle to work with Proxy's.  This causes hard-to-trackdown bugs in
> applications and mini-messes to deal with them since the app is forced
> to change its code to become "aware" of potential Proxy'iness of an
> object before comparing it with #=.
> This is no surprise, since writing a send to #== instead of #= for no
> more than "performance" is actually breaking encapsulation in the
> first place...
> There is an easy solution.  When writing #= and #hash implementations,
> use (#species or #xxxClass or #isKindOf: instead of #class) and #=
> instead #==.  So, for example, Eliot, I want to upgrade your new
> Message>>#= to something like:
> = anObject
>    ^self xxxClass = anObject xxxClass
>      and: [selector = anObject selector "selector lookup is by identity"
>      and: [lookupClass = anObject lookupClass
>      and: [args literalEqual: anObject arguments]]]
> Or #species or #isKindOf:, like we do in many other methods.  Now the
> method is Proxy-compatible.
> What do you think?

More information about the Squeak-dev mailing list