[aosd-discuss] "AOP considered harmful"

[Awais Rashid]

Dean,

Interesting point indeed. We are exploring similar ideas. You might be
interested in the following technical report. It discusses the notions of
dependency alignment, weak and strong orthogonality:

http://www.comp.lancs.ac.uk/computing/aose/papers/COMP-001-2004.pdf

Awais.

> -----Original Message-----
> From: discuss-bounces at aosd.net [mailto:discuss-bounces at aosd.net] On Behalf
> Of Dean Wampler
> Sent: 28 April 2005 01:57
> To: Ron Bodkin
> Cc: 'AOSD'
> Subject: Re: [aosd-discuss] "AOP considered harmful"
> 
> I've given some thought to applying Meyer's "Design by Contract" (DbC)
> to aspects and how aspects need to respect the contract of the advised
> code.
> 
> The Liskov Substitution Principal applies; If a class is substitutable
> for an interface, then the class+advice must be, too. This means that if
> a method in the class stipulates precondition A (conditions that must be
> met on entry to the function) and satisfies postcondition B (guaranteed
> results, if the preconditions are satisfied) and invariant C, then
> before advice needs to be contravariant with respect to A, convariant
> with respect to B, and invariant with respect to C.
> 
> "Contravariant with respect to A" means that the advice must stipulate a
> contract equivalent to A or /weaker/ than A; if it stipulated a contract
> /stronger/ than A, then it won't be substitutable for the class. A
> weaker contract is okay.
> 
> "Convariant with respect to B" means that it must guarantee to meet the
> postconditions B or /stronger/ conditions (again, to satisfy
> substitutability, it can't relax the "promise").
> 
> Finally, any invariants must be respected.
> 
> I've been working on a paper, which needs a lot of work, that discusses
> DbC in more detail (along with other design principles):
> 
> http://www.aspectprogramming.com/papers/AOPerspectiveOnOOD.pdf
> 
> dean
> 
> 
> Ron Bodkin wrote:
> > [snip]
> >
> > Re: the Liskov Substitution Principal and adherence to contracts, I
> think
> > most real systems have best efforts informal documentation of semantics,
> > which is far less than a contract. So what does it really mean that you
> can
> > substitute one subtype for another? How do you know what pre-conditions
> and
> > post-conditions apply?
> >
> > [snip]
> >
> > -----Original Message-----
> > From: Juri Memmert [mailto:memmert at jpmdesign.de]
> > Sent: Tuesday, April 26, 2005 10:20 PM
> > To: Bill Burke
> > Cc: AOSD; Ron Bodkin
> > Subject: Re: [aosd-discuss] "AOP considered harmful"
> >
> > -----BEGIN PGP SIGNED MESSAGE-----
> > Hash: SHA1
> >
> > Bill Burke wrote:
> >
> > [snip]
> >
> >>>I question this in practice in large OO systems. Without tools
> >>>support, finding the possible subclasses or implementers of something
> >>>is quite difficult, so knowing what actual implementation code will
> >>>execute is hard.
> >
> >
> > Yes and no. Unless you messed up your implementation, the Liskov
> > Substitution Principle still has to apply. And so you have a general
> notion
> > of the contracts the application will abide by. If you did break that
> > principle, you've already doomed your application to die a slow and
> > agonizing death.
> >
> > [snip]  ...
> 
> --
> Dean Wampler, Ph.D.
> dean at aspectprogramming.com
> http://www.aspectprogramming.com
> http://www.contract4j.org
> I want my tombstone to say:
>     Unknown Application Error in Dean Wampler.exe.
>     Application Terminated.
>     [Okay]    [Cancel]
> 
> __________________________________________________
> AOSD Discuss mailing list    -    discuss at aosd.net
> To unsubscribe go to http://aosd.net