Re: [aspectj-users] Question about Generic Aspects

[David Pearce <david.pearce@xxxxxxxxxxxxx>]

Hi Adrian,

Adrian Colyer wrote:
> The inter-type declarations refered to in that paragraph are
> inter-type method, field, and constructor declarations. The declare
> family are exempt from this restriction :)

Thanks for that!

So, I have another question about generic aspects.  Given what you've 
said I can do the following:

> aspect AddStudents<T> {
>
>  interface HasStudents {}	
>
>  declare parents : X implements HasStudents;
>	
>  List<Student> HasStudents.students = new ArrayList<Student>();
> }

To add a field to any class which is the type parameter of a concrete 
instance of AddStudents.  So,

> aspect FooStudents extends AddStudents<Foo> {}

Adds students to all instances of Foo. I kind of imagine that this will 
work in much the same way as C++ templates (i.e. some specialised aspect 
AddStudents__Foo is created with T replaced by Foo and FooStudents 
extending this).  Anyway, i also presume that if I have another aspect 
extending AddStudents where T=Foo then there will be a compile time error?

Right, so the case that I'm really interested is the following:

> public aspect Assoc<X,Y> {
>  interface HasXs {}	
>  interface HasYs {}
>	
>  declare parents : Y implements HasXs;
>  declare parents : X implements HasYs;
>	
>  public List<Y> HasYs.ys = new ArrayList<Y>();
>  public List<X> HasXs.xs = new ArrayList<X>();
> }

So, what I'm doing is effectively creating a bidirectional association 
between X and Y.  The thing is, I need to choose a name for xs and ys. 
This is annoying because it means I cannot have the following:

> aspect FooBarAssoc extends Assoc<Foo,Bar> {}
> aspect FooCarAssoc extends Assoc<Foo,Car> {}

Since, the ys name will clash.  So, my question (at last!) is: is there 
anyway around this ?  I guess what I really want to write is:

>  public List<Y> HasYs.XY_ys = new ArrayList<Y>();
>  public List<X> HasXs.XY_xs = new ArrayList<X>();

Where XY is just textually replaced with the actually type parameters.

Cheers,

Dave

> On 09/09/05, David Pearce <david.pearce@xxxxxxxxxxxxx> wrote:
>
> > Hi all,
> >
> > I have been reading the Aspectj 1.5 note book and have a question about
> > generic aspects, which I'm hoping someone can help me with.  The
> > documentation says:
> >
> > "The type parameter variables from a generic aspect declaration may be
> > used in place of a type within any member of the aspect, except for
> > within inter-type declarations."
> >
> > But, it seems that the example goes on to do just this. Namely:
> >
> > > public abstract aspect ParentChildRelationship<Parent,Child> {
> > > ...
> > >  declare parents: Parent implements ParentHasChildren<Child>;
> > > ...
> > > }
> >
> > So, I'm wondering whether I just missed something or, if not, which way
> > around it should be.
> >
> > Thanks,
> >
> > David J. Pearce
> >
> > --
> > Lecturer in Computer Science,
> > School of Mathematics, Statistics and Computer Science,
> > Victoria University of Wellington,
> > PO Box 600,
> > Wellington,
> > New Zealand.
> >
> > Office: Cotton 231
> > Telephone: +64 4 463 5833
> > URL: http://www.mcs.vuw.ac.nz/~djp
> > _______________________________________________
> > aspectj-users mailing list
> > aspectj-users@xxxxxxxxxxx
> > https://dev.eclipse.org/mailman/listinfo/aspectj-users


--
Lecturer in Computer Science,
School of Mathematics, Statistics and Computer Science,
Victoria University of Wellington,
PO Box 600,
Wellington,
New Zealand.

Office: Cotton 231
Telephone: +64 4 463 5833
URL: http://www.mcs.vuw.ac.nz/~djp