[squeak-dev] References to a removed and reloaded class

Levente Uzonyi leves at elte.hu
Fri Sep 21 20:13:28 UTC 2012

I guess we're going off the track with class renaming. The problem I'd 
like to solve is:
If we remove a class and then add a class to the system with the same 
name, then the methods which were referring to the class before the 
removal are still referring to the same old class. This means that two 
bindings will coexist in the system with the same class name, but pointing 
to different classes.

How is class renaming related to this?
One of the possible solutions is to move the removed class's binding to 
Undeclared. When you rename a class, then Class >> #rename: will check if 
there's a binding with the new class name in Undeclared. The problem here 
is that Undeclared doesn't release bindings automatically (when they are 
not referenced by any methods anymore), so bindings gone long ago are 
still lingering in Undeclared, therefore Class >> #rename: (and also Trait 
>> #rename:) will #inform: the user about it, which breaks one of the 

But there's another problem with this solution:
There's a test which tests if a removed class's method is still 
referencing to the class. So replacing the value of the binding with nil 
is not possible.
If we don't replace the value with nil, then the binding isn't really 
undeclared. So there will be bindings in Undeclared with non-nil value, 
which might have side effects in the system.

How does the solution I suggested work:
- when a class is removed, then its binding will be thrown away
- all methods referring to the class are recompiled. This means that if 
any such method exists, then a new binding will be created in Undeclared 
and all methods will use that new binding.
The drawback is that mass class removal will be slower. Removing a single 
class will have no noticable difference for the user (20-40ms+the 
recompilation time).

For completeness, here's a list of problems I don't want to solve now:
- Undeclared holding onto bindings forever
- Undeclared introducing Associations for classes instead of 
- how class renaming works

On Fri, 21 Sep 2012, Eliot Miranda wrote:

> I don't understand.  How else can one use Undeclared?  Any binding in a method which is undefined should be in Undefined.  Hence when a class is removed or when a class is renamed the binding should be moved to Undeclared and left

Some code uses #at:put: only, others try #includesKey: and #at:ifAbsent: 
which might not work as expected (see above).

> there, but when a class is renamed we can offer the user the opportunity to redefine methods that refer to the class with the old name (edit the methods to change the name to the new name).

Should a removed class's binding - which is still pointing to the class 
- be in Undeclared? Will it cause any issues that the binding is still 
pointing to the class?


> One might think that on rename the binding can be reused and its key changed.  But this would leave the methods referring to the new class but with their source naming the old name, hence on recompile the methods would now refer to
> the binding ... in Undeclared.  So the only correct thing for me is to move the binding to Undeclared, and, if interactive, offer up either a list browser of all references to the class, or an option to edit those methods
> automatically.
>       The only reason I know about Class >> #rename: is because a test was failing when I moved the binding to Undeclared. It might not be that hard to find the methods, but it's still extra work to be done. I'll check it out
>       though, because class renaming is definitely more rare than class removal.
>       Levente
> --
> best,Eliot

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