Hello Dave,

	Thank you for your answer! But the solution that you suggested does 
not show the use of reflection as I would like it to:

	o withArgs: theArguments executeMethod: theCompiledMethod.

I must make an explicit use of "withArgs:executeMethod" while I would 
like to make this use "transparent" to illustrate the "overriding" of 
the method invocation, any other suggestion?

	My purpose is to illustrate the use of reflection and differences 
between C++, Java, and Smalltalk with that respect.  I kind of 
remember that in some version/flavor of Smalltalk, you could 
"override" the VM mechanism to invoke method, typically by overriding 
some "withArgs:executeMethod:" when---and only when---using 
reflection so that performance would not be horrible but that you 
could still change the behaviour of invocations (at the risk of 
breaking the whole image if something silly was done, such as not 
"forwarding" the invocation to the VM after interception). Do I 
remember wrong?
	
	Yann

On 15/04/2013 13:59, David T. Lewis wrote:
> On Mon, Apr 15, 2013 at 01:17:40PM +0900, Yann-Ga?l Gu?h?neuc wrote:
>>
>> 	Dear all,
>>
>> I am trying to understand better reflection in Smalltalk. I am using
>> the latest version of Squeak (v4.3). I want to intercept every
>> message sent to instances of one of my classes. I assumed that I
>> could override the method `ProtoObject>>withArgs:executeMethod` but
>> St?phane (Ducasse) explained me that for performance reason, this
>> method is not used (this is my own summary of his answer). Which
>> method should I override / how could intercept sent messages?
>>
>> Here is the code of my attempt:
>>
>>      Object subclass: #C
>>      	instanceVariableNames: 'i'
>>      	classVariableNames: ''
>>      	poolDictionaries: ''
>>      	category: 'CSE3009'.
>>
>>      C class compile: 'newWithi: anInt
>>      	^(self new) i: anInt ; yourself.'.
>>
>>      C compile: 'withArgs: someArgs executeMethod: aMethod
>>      	Transcript show: ''Caught: ''.
>>      	^ super withArgs: someArgs executeMethod aMethod.'.
>>
>>      C compile: 'foo: aText
>>      	Transcript show: aText.
>>      	Transcript show: i.
>>      	Transcript cr.'.
>>
>>      C compile: 'i: anInt
>>      	i := anInt.'.
>>
>>      o := C newWithi: 42.
>>      o foo: 'This is foo: '.
>>
>> Executing this entire piece of code yields:
>>
>>      This is foo: 42
>>
>> When I would like to have:
>>
>>      Caught: This is foo: 42
>>
>> 	I was told about wrapper objects and MethodWrapper (see
>> http://stackoverflow.com/questions/15975340/interception-messages-in-squeak)
>> but in my quest to understand reflection, I would like to know if there
>> would be something more "reflective", typically overriding a message :-)
>>
>> 	Thank you very much in advance!
>> 	Yann
>
> Try this after compiling your code:
>
>    "Ask the class for the compiled method that you want to execute"
>    theCompiledMethod := C compiledMethodAt: #foo: .
>
>    "Make an array of size one containing the argument, a string"
>    theArguments := { 'This is foo: ' } .
>
>    "Execute the compiled method as if it was a message send to the object"
>    o withArgs: theArguments executeMethod: theCompiledMethod.
>
>    ==> Caught: This is foo: 42
>
> Dave
>
>

-- 
Yann-Gaël Guéhéneuc
Ph.D. et ing. / Ph.D. and eng.
Professeur titulaire / Full professor
Chaire de recherche du Canada sur les Patrons (de) logiciels /
   Canada Research Chair on Software Patterns and Patterns of Software
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