easy AOP right now using evil.rb

[Eric Mahurin]

Here is a pure ruby soluntion to doing AOP. You just need one
little method from evil.rb: Object#become. sub-classing and
then having the parent "become" the child is very similar to
the proposed "cut" (not sure about some of the management
facilities). Anyways, as soon as you require 'evil.rb' you
pretty much have it. You can get evil.rb here:

http://rubyforge.org/cgi-bin/viewcvs.cgi/evil/lib/evil.rb?cvsroot=evil

Here is a demo using this to get AOP:

require 'evil'

class A
def foo;"A";end
end

a = A.new
a.foo # => "A"

# first level "cut"
class B < A.clone # need a clone to prevent a loop
def foo;"["+super+"]";end
end
A.become(B) # replace parent with subclass

a.foo # => "[A]"

# second level "cut"
class C < A.clone
def foo;"{"+super+"}";end
end
A.become(C)

a.foo # => "{[A]}"

# restore the original functionality
A.become(B.superclass)

a.foo # => "A"

module Brackets
def foo;"["+super+"]";end
end

# "preclude"-like functionality
class D < A.clone
include Brackets
end
A.become(D)

a.foo # => "[A]"

Of course if we had this, it would be better to have a safer
Class#replace and that be able to break circular loops
automatically instead of having to use #clone to break the loop
manually.

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[Peter Vanbroekhoven]

Ah yes, this is what I expected.

We have been there you know. There's a reason why we've got a C version of
Florian's Object#become method on the Suby page. The problem with this
version is that A has become B. This means that the code that previously
defined, redefined and undefined methods in the original A, does that in B
now. The problem is that it is not possible to add a wrapper class this
way without breaking existing code, or at least without that code messing
with your advice. The behavior is almost the same, except that code needs
to be adapted to use these wrapper classes, and the basic idea behind AOP
is that that should *not* be so. We used this as an early test, but in the
end it had to go because it is obtrusive.

I'm sorry, but we're two years ahead of you you know.

Peter

[Trans]

> I'm sorry, but we're two years ahead of you you know.

Nonetheless. I am impressed that you thought of that Eric. You must
really be giving this a lot of thought. Give cuts some more careful
consideration. I am sure will ultimately come to understand why we
believe in them so.

T.