Monday, March 08, 2010 

Why you should learn AOP

A few days ago, I've spent some time reading a critic of AOP (The Paradoxical Success of Aspect-Oriented Programming by Friedrich Steimann). As often, I felt compelled to read some of the bibliographical references too, which took me a little more (week-end) time.

Overall, in the last few years I've devoted quite some time to learn, think, and even write a little about AOP. I'm well aware of the problems Steimann describes, and I share some skepticism about the viability of the AOP paradigm as we know it.

Too much literature, for instance, is focused on a small set of pervasive concerns like logging. I believe that as we move toward higher-level concerns, we must make a clear distinction between pervasive concerns and cross-cutting concerns. A concern can be cross-cutting without being pervasive, and in this sense, for instance, I don't really agree that AOP is not for singletons (see my old post Some notes on AOP).
Also, I wouldn't dismiss the distinction between spectators and assistants so easily, especially because many pervasive concerns can be modeled as spectators. Overall, the paradigm seems indeed a little immature when you look at the long-term maintenance effects of aspects as they're known today.

Still, I think the time I've spent pondering on AOP was truly well spent. Actually, I would suggest that you spend some time learning about AOP too, even if you're not planning to use AOP in the foreseeable future.

I don't really mean learning a specific language - unless you want/need to try out a few things. I mean learning the concepts, the AOP perspective, the AOP terminology, the effects and side-effects of an Aspect Oriented solution.

I'm suggesting that you learn all that despite the obvious (or perhaps not so obvious) deficiencies in the current approaches and languages, the excessive hype and the underdeveloped concepts. I'm suggesting that you learn all that because it will make you a better designer.

Why? Because it will expand your mind. It will add a new, alternative perspective through which you can look at your problems. New questions to ask. New concepts. New names. Sometimes, all we need is a name. A beacon in the brainstorm, and a steady hand.

As I've said many times now, as designers we're shaping software. We can choose many shapes, and ideally, we will find a shape that is in frictionless contact with the forcefield. Any given paradigm will suggest a set of privileged shapes, at macro and micro-level. Including the aspect-oriented paradigm in your thinking will expand the set of shapes you can apply and conceive.

Time for a short war story :-). In the past months I've been thinking a lot about some issues in a large CAD system. While shaping a solution, I'm constantly getting back to what I could call aspect-thinking. There are many cross-cutting concerns to be resolved. Not programming-level concerns (like the usual, boring logging stuff). Full-fledged application-domain concerns, that tend to cross-cut the principal decomposition.

Now, you see, even thinking "principal decomposition" and "cross-cutting" is making your first step into aspect-thinking. Then you can think about ways to bring those concerns inside the principal decomposition (if appropriate and/or possible and/or convenient) or think about the best way to keep them outside without code-level tangling. Tangling. Another interesting name, another interesting concept.

Sure, if you ain't using true AOP (for instance, we're using plain old C++), you'll have to give up some oblivousness (another name, another concept!), but it can be done, and it works fine (for a small scale example, see part 1 and part 2 of my "Can AOP inform OOP?")

So far, the candidate shape is causing some discomfort. That's reasonable. It's not a "traditional" solution. Which is fine, because so far, tradition didn't work so well :-). Somehow, I hope the team will get out of this experience with a new mindset. Nobody used to talk about "principal decomposition" or "cross-cutting concern" in the company. And you can't control what you can't name.

I hope they will gradually internalize the new concepts, as well as the tactics we can use inside traditional languages. That would be a major accomplishment. Much more important than the design we're creating, or the tons of code we'll be writing. Well, we'll see...

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Comments:
Quote of the day

"... or the tons of code ..."

Strange. I did not think that the software had a weight.
 
but then, my friend, you haven't been paying attention!!

Notes on Software Design, Chapter 3: Mass, Gravity and Inertia
 
We are sure that features of an authoritative point of view?

It could not be only your opinion, my friendly beloved?

After all the word software makes to think next to something that it does not have weight or at least that has some little, it does not agree?

In order it only makes us four laughed
:-))
 
H E R E T I C ! ! !
: )
 
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