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Re: [aspectj-users] Can an around advice for a constructor return a different Class of object?

You can return a subtype of expected result from the around-advice,
but not a supertype.  In this case, the pointcut


can pick out any subtype of List, e.g., ArrayList.  But 
NSMutableArray is not a subtype of ArrayList.

You can replace ArrayList with your own subtype of ArrayList:

   ArrayList around(int size) : call(ArrayList.new(int)) 
        && args(size) {
      return new MyArrayList(size);
   ArrayList around(Collection e) : call(ArrayList.new(Collection))
        && args(e) {
      return new MyArrayList(size);
   ArrayList around() : call(ArrayList.new()) {
      return new MyArrayList();

You might have to work around the costs of ArrayList in your
implementation, e.g., by implementing a dummy size:

   MyArrayList(int size) {

Sorry that Java type-safety won't permit what you want.

> ------------Original Message------------
> From: "Watkins, Garry" <gwatkins@xxxxxxxxxxxxxx>
> To: aspectj-users@xxxxxxxxxxx
> Date: Tue, May-30-2006 12:19 PM
> Subject: [aspectj-users] Can an around advice for a constructor return a different Class of object?
> I have a framework that I would like to use, that generates a bunch of
> ArrayList objects, what I would like to do is to trap the constructor 
> calls
> and replace the ArrayList with another type of List.  Is this possible?
> Basically, I want to create a ListFactory by using aspects.
> This is what I have currently:
> Object around(int capacity): call(!NSArray+ && List+.new(int)) &&
> within(org.objectstyle..*) && args(capacity){
>         return new
> NSMutableArray(capacity);
>     }
> However, I am getting a ClassCastException.  The NSMutableArray 
> implements
> the List interface.
> Thanks for any help.
> -- 
> Garry Watkins
> Database Administrator
> Motley Rice LLC
> 843-216-9639