Hi Javier,

Robert Hirschfeld maintains several Squeak packages which are in the problem
domain you describe. These are MethodWrappers, AspectS and PerspectiveS.
Rather than shortchange them and gloss over them here with a description,
I'll point you at:
http://www-ia.tu-ilmenau.de/~hirsch/Projects/Squeak/Squeak.html . From what
you describe, you should find MethodWrappers particularly useful.

Hope this helps,

Jim Benson



----- Original Message ----- 
From: "Javier Lanatta" <javier at lanatta.com.ar>
To: <squeak-dev at lists.squeakfoundation.org>
Sent: Sunday, November 30, 2003 3:15 PM
Subject: Redirecting messages on the VM


> Hi everybody,
> I'm doing a research work for my OOD class at university and I'm a
> little lost... So I come here looking for your help :) I'm sorry to tell
you
> that this email is gonna be kinda long, anyway I will try to write only
the
> most relevant things.
>
> For this research work I have to write a set of tools that allows
> the user to define what should be done when a given object receives a
given
> message.
> These are examples of what the tools must do:
> - When a given instance of RectangleMorph receives #addMorph: this
> should be logged and then the instance finally receives the #addMorph:
> - When any instance of Array receives #add: this message should be
> sent to the instance only if the add's argument belongs to a given class.
>
> I have most of the model finished. But I have problems intercepting
> the messages.
>
> By now I'm only trying to redirect every message to an object of a
> fixed class to another fixed object. Both the class of the first object
and
> the second object are stored in the Special Objects Array. Later I will
> replace the receiver with a fixed object that will act as an entry point
and
> it will redirect the message inside the "object's world" to other objects
> that will do all the work.
>
> I have tried two approaches without luck.
>
> 1.- Replace the receiver @ Interpreter>>internalActivateNewMethod
>
> I overwrote the receiver after the real receiver and its arguments are
> stored:
> ...
> ...
> "Copy the reciever and arguments..."
> argCount2 _ argumentCount.
> 0 to: argCount2 do:
> [:i | self storePointerUnchecked: ReceiverIndex+i ofObject:
> newContext
> withValue: (self internalStackValue: argCount2-i)].
>
> "here comes my code"
> rcvr _ self internalStackValue: argumentCount.
> self assertClassOf: rcvr is: (self splObj: MRFAux1).
> successFlag ifTrue:
> [
> self print: 'Intercepting...';cr.
> self storePointerUnchecked: ReceiverIndex+argumentCount ofObject:
> newContext withValue: (self splObj: MRFAux2).
> ].
> "and here it ends"
> ...
> ...
>
> MRFAux1: Contains the class of the object I want to intercept.
> MRFAux2: Contains the receiver.
>
> I guess I'm storing it in the wrong position... I have tried several
indexes
> without any good result.
>
>
> 2.- Send the message the same way a #doesNotUnderstand is sent @
> Interpreter>>lookupMethodInClass: class
>
> When the method is found in the dictionary I just send the message to the
> other object creating a message in the doesNotUnderstand fashion:
>
> ....
> ....
> found _ self lookupMethodInDictionary: dictionary.
> found ifTrue: [
> rcvr _ self internalStackValue: argumentCount.
> self assertClassOf: rcvr is: (self splObj: MRFAux1).
> successFlag ifTrue:
> self print: 'Intercepting @ lookupMethodInClass...';cr.
> self pushRemappableOop: (self splObj: MRFEntryPoint).
> self createActualMessageTo: (self splObj: MRFEntryPoint).
> rclass _ self popRemappableOop.
> messageSelector _ self splObj: MRFAux2.
> ^ self lookupMethodInClass: rclass
> ] ifFalse: [
> ^ methodClass _ currentClass
> ].
> ].
> ....
> ....
> MRFAux1: Contains the class of the object I want to intercept.
> MRFEntryPoint: Contains the receiver.
> MRFAux2: Contains the selector I want to send to the new receiver.
>
> In this case I cant compile the generated code :/
>
> ./release/gnu-interp.o: In function `findNewMethodInClass':
> //D/J4V13R/SqueakImages/TP/src/3.5.1/win32/gnu-interp.c:3388: undefined
> reference to `lookupMethodInClass'
> ./release/gnu-interp.o: In function `interpret':
> //D/J4V13R/SqueakImages/TP/src/3.5.1/win32/gnu-interp.c:6756: undefined
> reference to `lookupMethodInClass'
>
> I browse the gnu-interp.c file and the function lookupMethodInClass is
> missiong, if I remove the lines I added the code is ok... I have no clue
of
> what's going on.
>
> Is there a better way to do this? Where any of my ideas right? What was
> wrong in their implementation?
>
> Thanks in advance,
> Javier
>
>
> Some background information:
> Squeak Version: 3.6
> Virtual Machine: 3.5.1/Tea 1.9 VM (release) from June 21 2003 I've been
> using Squeak for about 9 months.
>
>
>