Aspect oriented Everything?

[Hung Jung Lu]

Steven Ketcham <stedak at charter.net> wrote in message 
> AOP was very difficult to explain, debug and implement. It did not 
> obviously replace any of our current procedures and at best it was 
> perceived as very heavy-weight. The conclusion on AOP was that it was a 
> neat concept but there was no immediate benefit for using it.
>
> On Sat, 23 Aug 2003 22:00:22 +0900, Lothar Scholz <llothar at web.de> wrote:
> > I don't like it because it breaks encapsulation and splitters the code
> > over a few files. Maybe that can be solved with new kind of editors
> > but it is much more easy to result in a big confusion.

AOP is the latest effort in code factorization. Code factorization
started with the goto statement, then loops, then functions, then
classes and methods. And now, AOP.

If you write programs in OOP long enough, you will realize that there
are code spots that are not factorized. For example, you register to a
event listener at the beginning and de-register at the end of a
method. If you find yourself writing very similar codes in various
classes or methods all over places, you are not factoring your code
efficiently. It's not your fault, it's just that OOP cannot do certain
types of code factorization.

Before having loops, a repetitive task may look like

x = x + 1
x = x + 1
x = x + 1

But when you have loops, you can factor the three lines of code into

for i in range(3):
    x = x + 1

Similarly, before object-oriented programming, you have data structure
that are very similar, say, A and B, A has (color, shape) and B has
(color, shape, weight), with OOP you can use inheritance, and factor
out the common code.

If we view OOP and inheritance as a vertical dimension in code
factorization, AOP would be a new horizontal dimension in code
factorization. Hence, people use terms like "aspect weaving".

Some people don't like AOP because it violates encapsulation in the
vertical dimension. But this way of thinking is kind of, erh,
unidimensional. Because conversely, a program that is built from
purely AOP is encapsulated in its own aspect dimension, and the usage
of OOP in that case would violate the encapsulation in the horizontal
dimension. The fact is, both factorizations are needed in the real
world. Aspect-oriented coding and object-oriented coding are like the
conjugate variables in quantum mechanics, whether you use one picture
or the other, at the end of the day they are equivalent, but in some
circumstances it's better to use one than the other. (If you know
Fourier transform, you know what I mean. A localized wave packet in
time necessarily means a spread-out packet in frequency, and
vice-versa. You can't have encapsulation both ways.)

regards,

Hung Jung