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

[Nicolas Cellier]

2015-04-04 14:55 GMT+02:00 Max Leske <maxleske at gmail.com>:

>
>
> 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.
>

Nope, no problem, I think we just use the identityHash, so nowhere a symbol
is required.
It's only a problem at higher level, image-side, for IDE.


>
> 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>:
>
>> 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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