(fwd) Fw: Self question: interception of assignments
Jecel Assumpcao Jr
jecel at merlintec.com
Fri Jul 8 22:11:30 UTC 2005
Here is a reply to an email I received that I thought someone in the
list might have a better solution to than mine.
----- Original Message -----
From: "Jecel Assumpcao Jr"
To: "Ellen Van Paesschen"
Sent: Wednesday, July 06, 2005 5:10 PM
Subject: Re: Self question: interception of assignments
> I am forwarding this to the self-interest mailing list so that more people
> can look at your problem and perhaps come up with a better solution.
>> can you help me out with this: how can I intercept assignments in Self;
>> say every time an assignment is performed I want to trigger another
> The normal way it has been done in Self is to hide the real data and
> assignment slots with a name like rawSomething and then use a regular
> method to add your action before or after the assignment. You probably
> have seen things like
> ( | rawSalary <- 0.
> salary = (rawGrade).
> salary: v = (rawGrade: v. updateStatistics).
> | )
>> Since these method slots contain the assign primitive I tried wrapping
>> assignments dynamically but I am stuck due to the nr of arguments
>> wrap: sel = ( | m. new. old. sel2 |
>> m:(reflect: self).
>> old: ((m at: sel) correspondingAssignmentSlot). "here is now the <-
>> sel2: (old storedName). "the original assign selector"
> Please note the word "corresponding". The way Self is implemented the
> assignment slot must have the same name as the data slot with ':' added to
> it. A lot of things will stop working if you break this assumption.
>> m at: 'tempy:' PutContents: (reflect: old). "error since wrong nr of
> If old is a slot then (reflect: old) is a mirror on the slot and not on
> the actual method. Such an object can only be placed on a data slot which
> takes zero arguments. This might be the cause of the error you are seeing.
> In theory you could do "old value" instead (if it were a regular method),
> but in this case that will just get you a mirror on the string '<-' which
> doesn't help at all.
>> new: ('| :arg1 | triggerAction . tempy: arg1') parseObjectBody.
>> m at: sel2 PutContents: new.
>> Can I avoid this or is there a more simple way to intercept assignments?
> The most recent version of Self (4.2.1) allows you to store method objects
> in slots, but that is enabled by default and I don't see a simple way in
> which that would help with your problem. I think the only way to do it is
> patching the object like you are doing. You might want to check out the
> method 'changeSlotInObjectTo:' in "traits slots plain" or something
> similar to rename the original slots adding 'raw' to their names and then
> creating two additional methods.
> You might find a related discussion from 1994 interesting:
> -- Jecel
Here was the reply:
thanks for the response - I didn't find a straightforward solution
and since we were limited by a paper deadline, I implemented some
kind of assignment "shadowing". A new child object is created that
overrides the assignment with some action to be triggered and then a
resend to the original assignment. All references to the object
containing the original assignment are then set to the new child
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