Re: [aspectj-users] One target for intertype declarations

[David Pearce <david.pearce@xxxxxxxxxxxxx>]

Hi Eric,

> ITDs cannot hold aspect instances since normally such instances
> cannot be created by hand. Google for "association aspects" for a
> different approach.

Ok, but that's a minor difference since all I want is to associate state 
with an object.  So, it doesn't have to be an aspect instance --- a 
simple data structure holding my state will suffice.

> > Is the reference put into all objects
> > matching the pertarget pointcut, or just into objects for which an
> > aspect is created?   
>
> Isn't that the same? One aspect instance is created for any object
> matching the pertarget pointcut.

Well, I was thinking of something along the following lines:

aspect myAspect pertarget(initialization(*.new()) {
 static int counter = 0;

 before() : initialization(*.new(..)) && !within(myAspect)
	    && if(++counter > 100) {
   ...
   counter = 0;
 }
}

The point about this is that the advice is only entered every 100th 
time.  Meaning that an aspect is only created every 100th time.  So, the 
question is, is there an empty (aspect) reference field for objects 
which match the pertarget specifier, but never make it into the advice?

The reason I want to do this is simply to associate state with "some" 
objects, rather than all (i.e. Sampling).  Furthermore, i would rather 
not have any memory overhead associated with those which have no state 
associated with them.

One a slightly different note, one thing does occur to me in the 
pertarget versus ITD discussion.  Consider the following alternative:

aspect myAspect {
    private interface State {};
    declare parents: * && !java.lang.Object implements State;
    MyState State.ref = null; // will point to my associated state

    ...
}

I think that State.ref will be introduced into every class, meaning 
objects composed using inheritance will have multiple copies of it?  In 
this case, there is a difference from pertarget, where I presume there 
can only ever be one reference per object.  Comments?

Cheers,

Dave

> Eric
>
> - -- 
> Eric Bodden
> Chair I2 for Programming Languages and Program Analysis
> RWTH Aachen University
>
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