Re: [abc-users] Tracematch vs aspect variable binding

Hi Alan,

> What changes do I need to make to the aspect so that it is equivalent to
> the tracematch? I was thinking of writing code to compare the object
> that is currently being evaluated on the aspect (i.e. compare
> a2.equals(a1) ), but that looks a bit naive to me. I am fairly new to
> aspect oriented programming, so I might have made a elementary mistake
> somewhere in my aspect, and I would appreciate some help on this matter.

As you see, the code generated by the tracematch implementation results in the
kind of matching you expect -- all the symbols in a particular filtered trace
have the same binding of the 'a' variable. In AspectJ, there is no such
restriction, and each piece of advice matches independently to all others. In
particular, this means that while you have '&& target(a)' in both pointcuts
in the aspect, that just associates the name 'a' with the target of the
method call, but doesn't impose any further conditions.

Thus, essentially your aspect maintains one withdrawal counter and one deposit
counter *for all Account instances*, rather than a separate pair of counters
for each instance.

The way to achieve tracematch-like behaviour is to store the counters in a
Map, say, associated with the Account for which they are. Each piece of
advice would then look up the relevant counters to 'a' and update/read them.
Alternatively, you could introduce the counters as intertype fields onto the
Account class, and use a.countwd and a.countdp in your advice.

Hope this helps,
- Pavel
Received on Thu Feb 14 2008 - 13:42:31 GMT