2015-01-07 18:25 GMT+01:00 Nicolas Cellier <
nicolas.cellier.aka.nice at gmail.com>:

>
> ---------- Forwarded message ----------
> From: Nicolas Cellier <nicolas.cellier.aka.nice at gmail.com>
> Date: 2015-01-04 11:30 GMT+01:00
> Subject: Re: [squeak-dev] A puzzle for the New Year
> To: The general-purpose Squeak developers list <
> squeak-dev at lists.squeakfoundation.org>
>
>
> Ah, you mean like
> http://stackoverflow.com/questions/27386061/overriding-compile-method-in-squeak/27413079#27413079
>
> A picture is worth a few dozen of words indeed.
>
> I'm pretty sure I saw a browser showing the whole metaclass hierarchy in
> the past which also might be helpfull to better understand these corners,
> but I just don't remember where exactly (st-80 v2.3?).
>

Oh I just see it now, still there in Squeak trunk after all these years!!!

Select a class, select the class side button, and operate the pop up menu
'show hierarchy'. It's not as powerfull as a Hierarchybrowser, but is
already someting.


>
> 2015-01-02 12:01 GMT+01:00 Trygve Reenskaug <trygver at ifi.uio.no>:
>
>>  Hi,
>> I had to dive into  the deeper regions of Smalltalk when I was preparing
>> BabyIDE for Monticello. I needed to specialize a class  *fileOut *method:
>>
>> BB5aMoneyTransferContext>>fileOutOn: aFileStream moveSource: moveSource
>> toFile: fileIndex initializing: aBool
>>     super fileOutOn: aFileStream moveSource: moveSource toFile: fileIndex
>> initializing: aBool.
>>     <my own additions>
>>
>> This works, but the *fileOutOn:moveSource:toFile:initializing:*-method
>> is defined in class *Class* which is not a superclass of
>> *BB5aMoneyTransferContext*. So *super *does not refer to the superclass!
>> What's going on?
>> --------------------------------------------------
>> There are two essential object structures in Smalltalk: The instantiation
>> tree and the class inheritance tree. They are independent but intertwined
>> as described in chapter 16 of the Blue Book. It's pretty complicated in the
>> general but fairly obvious in this concrete example.
>>
>> Smalltalk is all about objects, not classes.  I used my *Smalltalk
>> Reverse Engineering (SRE)* tool and produced the attached object
>> diagram. The notation in the diagram is
>>
>>    - a rectangle represents an object
>>    - the object's name is [<oop>] : <class name>
>>    - a line represents a link. An 'instanceOf' relationship is marked */self
>>    class*; an inheritance relationship is marked *superclass*.
>>
>> The diagram shows that the answer to the puzzle is one 'instaceOf'
>> relationship followed by four  'superclass' relationships. The departure
>> from the usual is that while most class objects are instances of their own
>> Metaclass. ProtoObject is an exception. It has no superclass, but its
>> metaclass has. It is class Class. Add to this that when an object receives
>> a message, it goes to its class to find the corresponding method.
>> [1224]:MoneyTransferContext  receives the super fileout message. The VM
>> goes to  the superclass of its class, [3253]:Metaclass and looks for the
>> required method in its methodDict. It doesn't find it and continues up the
>> superclass chain until it finds it in [1254]:Class class . Straight
>> forward, isn't it.
>>
>> I hope you enjoy this dive into the innards of Smalltalk and wish you all
>> A Happy New Year!
>> --Trygve
>>
>>
>>
>>
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.squeakfoundation.org/pipermail/squeak-dev/attachments/20150107/ea226758/attachment.htm