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[aspectj-users] pertarget anomaly (was: bug with pertarget?)
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Hi all,
Well, i'm still chasing up a few things regarding use of pertarget. One
thing I want to do is associate state with objects which are constructed
and then monitor modifications to their fields. The following gives an
example:
public aspect taspect pertarget(call(*.new(..)) && !within(taspect)) {
after(Object o) : target(o) && call(*.new(..)) && !within(taspect) {
System.err.println("CONSTRUCTING - " + o);
}
after(Object o) : target(o) && set(* *.*) && !within(taspect) {
System.err.println("SETTING - " + o);
}
}
public class test {
public int testField;
public static void main(String argv[]) {
test t = new test();
t.testField = 0;
}
}
However, this does not work - neither "CONSTRUCTING - ..." nor "SETTING
- ..." messages are printed. According to Ramnivas Laddad in his reply
to my previous mail on this topic (see "re: bug with pertarget?"), the
reason for this is:
This is due to implicit limiting of join points when using any of the per- associations.
For pertarget() associations, the advice application (or the scope of aspect) is
limited to where the join point’s target object matches the aspect’s associated object
(target object at call(test.new(..))).
So, the alternative implementation of the aspect is:
public aspect taspect perthis(execution(*.new(..)) && !within(taspect)) {
after(Object o) : target(o) && execution(*.new(..)) && !within(taspect) {
System.err.println("CONSTRUCTING - " + o);
}
after(Object o) : this(o) && set(* *.*) && !within(taspect) {
System.err.println("SETTING - " + o);
}
}
However, this does not (of course) catch the setting of testField in
test.main(). So, it seems I cannot express what I want using pertarget,
although it is certainly possible to hand code it via inter-type
declarations of the kind discussed in perious mails.
Anyway, I think that the first case above should work, since the
pertarget specifier is really saying which objects the advice will work
on. So, while the target of call(*.new(..)) is strictly null, it is
clear which object it applies to and this object can be accessed via
after() returning(Object o) mechanism.
Cheers,
Dave
