[Vm-dev] Re: [Pharo-dev] Binding semantics of SystemDictionary

Max Leske maxleske at gmail.com
Sat Apr 4 12:55:46 UTC 2015


> On 31 Mar 2015, at 23:12, Nicolas Cellier <nicolas.cellier.aka.nice at gmail.com> wrote:
> 

Thanks Nicolas. I was hoping to see a bit more activity on this thread so I didn’t reply immediately.

> not only the globals but the methods in MethodDictionary too :)

Ok, that might even be worse. AFAIK MethodDictionary is treated as a special class by the VM. So storing other objects in there may be a real problem, not just a philosphical one. CC’ing vm-dev on this.

> It might be a feature, it's just that it's unused because of limited IDE and compiler.

If you look far enough, almost anything can be considered a feature… :)

> 
> 2015-03-31 20:49 GMT+02:00 Max Leske <maxleske at gmail.com <mailto:maxleske at gmail.com>>:
> Hi
> 
> Tommaso and I, while hacking on Fuel, today discovered that globals in Pharo can have very weird bindings (I guess some of you already know that). For example:
> 
>         class := Class new
>                 setName: 4;
>                 yourself.
>         Smalltalk
>                 at: class name
>                 put: class.
> 
> So we now have a class with name 4 (which is a SmallInteger):
> 
>         self assert: (Smalltalk at: 4) == class.
> 
> 
> There are basically two different issues:
> 1. SystemDictionary will store any kind of association, not only symbols / strings
> 2. SystemDictionary is an IdentityDictionary and as such two equivalent but not identical keys will not resolve to the same object:
> 
>         class := Class new
>                 setName: (String streamContents: [ :s | s nextPutAll: 'someName']);
>                 yourself.
>         Smalltalk
>                 at: class name
>                 put: class.
> 
>         Smalltalk
>                 at: (String streamContents: [ :s | s nextPutAll: 'someName’])
>                 ifAbsent: [ false ]. “——> false”
> 
> 
> In Fuel we simply assume that any key to a global is either a ByteString or ByteSymbol. If that’s not the case bad things happen.
> It would help us a lot if we could clear up the semantics of bindings in SystemDictionary:
> 1. Are bindings with keys that are not ByteString or ByteSymbol valid?
> 2. Should we keep allowing ByteString as keys to globals (ByteSymbol guarantees identity)?
> 3. If we allow ByteString, do we also allow WideString?
> 4. Would “type checks” on SystemDictionary incur a big performance penalty?
> 
> 
> Any suggestions are welcome.
> 
> Cheers,
> Max
> 

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