Re: [aspectj-users] Just for fun: declare error to prevent use of inheri

[Matthew Adams <matthew@xxxxxxxxxxxxxxx>]

Interesting.  I like all of the suggestions.  I entered an issue to track this:

https://bugs.eclipse.org/bugs/show_bug.cgi?id=387499

Thanks!

On Thu, Aug 16, 2012 at 3:05 PM, Andy Clement <andrew.clement@xxxxxxxxx> wrote:

I haven't spent toooo long thinking about it, but I don't think you
can at the moment. We don't really have the capabilities to introspect
the class hierarchy to that level of detail.

Some made up syntaxes:

If 'Object+' indicates subtypes, let's add a numeric to indicate distance:
declare error:  within(Object+2): "Type does not directly extend
object"; // maybe add the type category type pattern too:
within(is(ClassType) && Object+2)
declare error: within(Object+>2):   "Type does not directly extend object";

More direct:
declare error within(!extends(Object)): "Type does not directly extend
object"; // if 'extends' is strictly looking at the declared type and
not the inheritance chain.

You could probably cause an error if you tried to use declare parents
extends with a simple type because extends will report an error if the
new type doesn't have the same parent as the existing type:

class Foo1 {}
class Foo2 extends ArrayList {}

class Marker {}

aspect X {
  declare parents: Foo* extends Marker;
}

will give an error ... but it isn't as simple as a nice message saying
'type Foo2 doesn't directly extend Object.'

cheers,
Andy

On 16 August 2012 08:40, Matthew Adams <matthew@xxxxxxxxxxxxxxx> wrote:
> Just for fun, I was trying to think of how to use declare error to prevent
> the use of class inheritance in user code, but I can't think of how to do
> that.
>
> Basically, if you wanted to disallow the declaration of classes that extend
> anything other than Object, is there a "declare error" form that would work?
>
> -matthew
>
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