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Re: [aspectj-users] set() capture oldvalue
It's true in this particular application, the performance of reflection won't 
kill the application.
But it's just something that I feel is missing from the language.
I wanted to see what other use cases might exist.
Performance could be a problem in some cases.


Tim Schafer
tschafer@xxxxxxxxxxx



----Original Message Follows----
From: Matthew Webster <matthew_webster@xxxxxxxxxx>
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To: aspectj-users@xxxxxxxxxxx
Subject: Re: [aspectj-users] set() capture oldvalue
Date: Mon, 16 May 2005 07:50:11 +0100
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Tim,

If you have a concern about the performance of something measure it. Many
frameworks use performance. I don't believe it's impact on overall
application performance will be as bad as you think.

Matthew Webster
AOSD Project
Java Technology Centre, MP146
IBM Hursley Park, Winchester,  SO21 2JN, England
Telephone: +44 196 2816139 (external) 246139 (internal)
Email: Matthew Webster/UK/IBM @ IBMGB, matthew_webster@xxxxxxxxxx
http://w3.hursley.ibm.com/~websterm/

"Tim Schafer" <tschafer@xxxxxxxxxxx>@eclipse.org on 13/05/2005 19:11:36

Please respond to aspectj-users@xxxxxxxxxxx

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cc:
Subject:    Re: [aspectj-users] set() capture oldvalue


That's exactly what I'm doing.
Using reflection.
I'm concerned about performance.
If I were using aspects I wouldn't use refelection in each setter to get
the
old value.
The aspect compiler should be able to do this work for me.
I believe it's a major defeciency that this isn't avaiblable.
Are there already plans to fix this?
Should I file a bug?

Tim Schafer
tschafer@xxxxxxxxxxx



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From: Matthew Webster <matthew_webster@xxxxxxxxxx>
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Tim,

I'm sure there was a thread on either aspectj-users or aspectj-dev but I
can't find it. Bottom line is the existing field value is not a property of
the join point so you must get it directly. The simple examples below shows
you how to use reflection or direct access:

public class SomeClass {

       private int intField;

       public void setInt (int i) {
             intField = i;
       }
}

public aspect Aspect {

       pointcut fieldSet(int newValue) :
             set(* SomeClass+.*) && args(newValue)
             && withincode(* SomeClass+.set*(..))
             ;

       before (int newValue) : fieldSet (newValue) {

             Object oldValue = null;
             try {
                   Class clazz =
thisJoinPoint.getSignature().getDeclaringType();
                   String fieldName =
thisJoinPoint.getSignature().getName();
                   Field field = clazz.getDeclaredField(fieldName);
                   field.setAccessible(true);
                   oldValue = field.get(thisJoinPoint.getThis());
             }
             catch (Exception ex) {
                   ex.printStackTrace();
             }
             System.out.println("? beforeFieldSet() oldVaue=" + oldValue +
", newValue=" + newValue);
       }
}

public privileged aspect PrivilegedAspect {

       pointcut intFieldSet(SomeClass obj, int newValue) :
             set(* intField) && target(obj) && args(newValue)
             && withincode(* SomeClass+.set*(..))
             ;

       before (SomeClass obj, int newValue) : intFieldSet (obj,newValue) {
             int oldValue = obj.intField;
             System.out.println("? beforeIntFieldSet() oldVaue=" + oldValue
+ ", newValue=" + newValue);
       }

}

Matthew Webster
AOSD Project
Java Technology Centre, MP146
IBM Hursley Park, Winchester,  SO21 2JN, England
Telephone: +44 196 2816139 (external) 246139 (internal)
Email: Matthew Webster/UK/IBM @ IBMGB, matthew_webster@xxxxxxxxxx
http://w3.hursley.ibm.com/~websterm/

"Tim Schafer" <tschafer@xxxxxxxxxxx>@eclipse.org on 11/05/2005 21:47:44

Please respond to aspectj-users@xxxxxxxxxxx

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cc:
Subject:    [aspectj-users] set() capture oldvalue


I've used the following pointcut to capture all field modifications that
occur within a setter method.

pointcut fieldSet(Object newValue) : set(* SomeClass+.*) && args(newValue)
&& withincode(* SomeClass+.set*(..));

I can capture the new value, but I can't capture the old value without
resorting to reflection.
In theory aspectJ could provide access to the old value more statically.
But aspectJ doesn't seem to support this.
Or am I missing something?


Tim Schafer
tschafer@xxxxxxxxxxx


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