RE: [aspectj-users] type casting

[<kviggers@xxxxxxxx>]

A once saw a proposal for a cast join point. Here is the link:

http://quercusseg.unex.es/jclemente/phdoos03/papers/paper1.pdf


> -----Original Message-----
> From: aspectj-users-admin@xxxxxxxxxxx [mailto:aspectj-users-
> admin@xxxxxxxxxxx] On Behalf Of Wes Isberg
> Sent: November 23, 2003 10:17 AM
> To: aspectj-users@xxxxxxxxxxx
> Subject: Re: [aspectj-users] type casting
> 
> Frank Xia wrote:
> 
>  > As I understand, current AspectJ 1.1 doesn't have a join point to catch
>  > typing casting but does anyone have any clever workaround? If not,
> anyone
>  > know when AspectJ would extent to have this kind of join point?
> 
> Interesting!
> 
> As far as I know, no one has suggested a cast join point.
> 
> There is no workaround that I know of, though you can advise any
> join point throwing ClassCastException:
> 
>     after() throwing (ClassCastException e) : ... {}
> 
> 
> As for a cast join point, it seems feasible to implement the
> join point for explicit cast operators using either source
> or bytecode (checkcast takes the type being cast-to).
> 
> What would you use it for?
> 
> Assuming the docs:
> 
>    - cast(Type)
>    This picks out join points where a reference is being cast to Type.
>    The reference being cast is available as target at this join point.
>    {optionally: the type being cast-to is available as the single
>     argument at this join point, as a variable of type Class.}
> 
> Here's one use case, to log:
> 
>    after(Object ref, Class c) throwing (ClassCastException e) :
>            cast(Runnable) && target(ref) && args(c) {
>        log(e + " after casting " + ref + " to " + c);
>    }
> 
> Here's another use case, to throw your own exceptions.  You could
> even do so when there wouldn't be a ClassCastException.
> 
>    before(MyRunnable runner) : cast(Runnable) && args(runner) {
>        throw new CastError(runner, Runnable.class);
>    }
> 
> Here's another definition and use case:
> 
>    - cast(TypePattern)
>    {ditto} any type matching TypePattern
> 
>    declare error : cast(*) && within(com.company.internal.critical..*) :
>       "casts not permitted in critical code";
> 
> Other use cases?
> 
> Jim once stated a standard for new language features as
> 
>    needs to have both a convincing example of where it is a real and
>    important problem as well as a fairly concrete proposed solution.
> 
> I believe that this has a concrete solution [but I'm not the
> compiler writer], so the main question is whether the added
> language complexity is worth the benefit of the use cases.
> 
> Thanks -
> Wes
> 
> P.S. - I haven't thought about it carefully enough to know that there
> are no implicit casts that resolve to a cast operator.  It will confuse
> developers to find join points not reflected in source. Conversely,
> some cast operators are superfluous; I'm not sure the compiler isn't
> permitted to optimize them away, confusing the developer who expected
> a join point there.  If the join point doesn't follow expectations,
> then we have to take into account that users might be confused when
> the join point is surfaced using AspectJ when considering whether to
> add it to the language.  I.e., I think a new join point should be
> part of the existing programmer's model or a clear extension to it.
> 
> 
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