[Pharo-dev] Slot class builder: Anonymous class modification

Igor Stasenko siguctua at gmail.com
Fri Nov 22 10:25:56 EST 2013

On 22 November 2013 16:04, Camille Teruel <camille.teruel at gmail.com> wrote:

> Hi everyone,
> With Esteban, we bumped into a problem with anonymous subclasses and the
> slot class builder.
> The problem is that once an anonymous class is created is not possible to
> modify it.
> Here is the problem:
> For creating an anonymous class with the new class builder API you do
> something like:
> myAnonymousClass := AnonymousClassInstaller make: [ :classBuilder |
>         classBuilder
>                 superclass: Object;
>                 name: #MyAnonymousClass;
>                 .... ]
> What happens is that the class builder asks the class installer if the
> class named #MyAnonymousClass exists or not to know if this a class to be
> created or to be modified.
> Here, the strategy of the anonymous class installer is to always answer
> no. So ok, now you have you're anonymous class.
> But what happens when you do something like:
> myAnonymousClass addInstVarNamed: #newIV
> Since the class has no clue of what class installer was used to create it,
> it instantiate a new one, and a PharoClassInstaller !
> This new class installer then says to the class builder that there is no
> class named MyAnonymousClass so it creates it! And it install it in the
> system dictionary!
> And myAnonymousClass is not modified.
> So there is several problem here:
> - a class doesn't know which class installer was used to create it
> - even if the class would know that, the anonymous class installer would
> always say that it doesn't know it and a new class would be created
> So one possible solution for that is to have one class installer per
> environment (so add one iv in SystemDictionary right now), like that a
> class would know what class installer was used to create it.
> What would happen then is that you don't create anonymous classes anymore,
> that is to say a class not installed in any environment, but instead you
> create a class that exist in an environment separated from the system
> dictionary.
> What do you think?
> i think that this expression:

myAnonymousClass addInstVarNamed: #newIV

should create and answer new original class.
And don't take me wrong a 'new class' means just a new class object, which
is not installed/registered anywhere, because it is done at next step (if
its necessary).

I'm not sure what this 'class installer' thingy comes from and it looks
completely irrelevant. We must have clear separation between operations
which creating new classes
and installing/registering them inside environment.
Because anonymous class is not one which has no name, it is one which is
not registered in any public place. For the rest , it should behave in same
way as public one.

The fact that IDE tries to hide it and simulate as if you modified existing
class is not really important here, because it is higher-level
contracts and responsibilities.

Best regards,
Igor Stasenko.
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