Skip to main content
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [List Home]
Re: [aspectj-users] Pointcut to calls to a specific field 
Hi Bruno -

This is actually a really good example of thinking in terms of
join points (pointcuts, advice) and not code manipulation or
generation.  Though there is only one bit of code

    thing.field.add(something)

there are at least two join points (field-set, call).
> I'm still not happy with the field test in the advice. Is there really 
> no static way to capture field specific join points?

The field-specific join points are get() and set().

The call join point only knows that it has a reference;
it doesn't know that it is a field.  Conceptually you
should think of it as different join points, something like

  load reference from field
  make call

You pointed this out in saying
> I've
> found the get-access definition, but I don't see a way to connect it to 
> a following call.

As for this:

> And the join point annotations in
> Eclipse still show up at the local Collection.add() calls.

As you point out, if() is a dynamic test, so the
static shadow of the pointcut will be on all the
call(boolean Collection.add(Object)) call join points.
If the field is private, you could safely staticly limit
the advised join points to calls within the declaring class:

  call(boolean Collection.add(Object)) && within(MyContainer)

If the field incidentally is the only collection, you might
be able to combine within() and withincode() with call to
"accidentally" only specify calls to the field, and leave out
the dynamic if() test. In that case you might
also specify some declare-warnings to signal when other
collections are added to the class.  (This is not really an
approach I recommend, but I've seen it work for some situations.)

Another approach is to proxy the field and put the crosscutting
behavior in the proxy.  You'd use advice to replace the field
when it is set with your proxy that delegates to a collection,
and your proxy class would implement whatever policy you needed.

Wes

Bruno Feurer wrote:


Hi,

I'm still not happy with the field test in the advice. Is there really
no static way to capture field specific join points?

A new idea is to test the field reference within the pointcut
definition:

  pointcut add(MyContainer container, Object child, Collection c) :
      call(boolean Collection.add(Object)) && this(container) &&
      args(child) && target(c) && if(c == container.children);

This works also with a "clean" advice. But we still need the Collection
parameter for the if statement. And the join point annotations in
Eclipse still show up at the local Collection.add() calls.

Has somebody a hint or a correction to my approaches? There must be
several situations for capturing calls to specific field members. I've
found the get-access definition, but I don't see a way to connect it to
a following call.

Thanks,
Bruno




-----Original Message-----
From: aspectj-users-admin@xxxxxxxxxxx [mailto:aspectj-users-admin@xxxxxxxxxxx] On Behalf Of Bruno Feurer 
Sent: Friday, June 18, 2004 16:16
To: aspectj-users@xxxxxxxxxxx
Subject: [aspectj-users] Pointcut to calls to a specific field


Hi there,
how can I define a pointcut picking out calls to specific field? 
 ...
 this.children.add(someObj);
 ...

definitions like

 pointcut add(MyContainer container, Object child) :
call(boolean Collection.add(Object)) && this(container) && args(child); 

also match

 ...
 Collection c = new ArrayList();
 c.add(someObject);
 ...

So I came up with the following solution:

 pointcut add(MyContainer container, Object child, Collection c) :
     call(boolean Collection.add(Object)) && this(container) &&
args(child) && target(c);
after(MyContainer container, Object child, Collection c) : add(container, child, c) { 
     if (c != container.children)
         return;
     ...
 }
Has somebody found a better solution? Some definition limiting the pointcut only to a specified field or something alike? 

Thanks for any ideas,
Bruno Feurer

_______________________________________________
aspectj-users mailing list
aspectj-users@xxxxxxxxxxx http://dev.eclipse.org/mailman/listinfo/aspect> j-users 




_______________________________________________
aspectj-users mailing list
aspectj-users@xxxxxxxxxxx
http://dev.eclipse.org/mailman/listinfo/aspectj-users

Back to the top