AOP use cases

[Jacek Generowicz]

"Daniel Dittmar" <daniel.dittmar at sap.com> writes:

> Jacek Generowicz wrote:
> >>>           SEPARATION OF CONCERNS. [snip]
> 
> C moved the I/O from the language to a library. This is separation of
> concerns

Not really. By separation of concerns I mean:

  Where previously you had to keep two orthogonal goals in mind in a
  single chunk of code, you now deal with each goal separately.

Stupid example:

  def foo(a):
      print "before", a
      a.sort()
      print "after", a
      ...
      print "before", a
      a.reverse()
      print "after", a

  foo(bar)

In the above you are manually mixing the concern of modifying an
object, with the concern of tracking its changes. In the following you
separate them.

  # Worry about the modifications you want to make
  def foo(a):
      a.sort()
      ...
      a.reverse()

  # Worry about tracking changes to an object
  class mutation_reporter:
      def __init__(self, obj):
          self.obj = obj
      def __getattr__(self, name):
          if name in mutating_methods:
              print "before", self
              self.blah(name)
              print "after", self
      def __setattr__(...):
          ...

  # Weave together the separate concerns.
  foo(mutation_reporter(bar))


Is this AOP? Should I care?

Is it useful? Should I care?

(I guess the way one answers questions 2 and 4, is ... err
... interesting.)