"restoring" classes after changing stuff

ruby-talk
1

Hi,

Well, I'm new to Ruby (I've been working and playing with it for the
last 6 months only), and
I know there's probably another way in which this could work, but
somehow I feel like the
code below should work. Let's see what you guys think about it.

The idea is making a copy of a class object, changing it and then
restoring it back to what it was after playing with the new stuff I
added. It should go somewhat like this:

OldArray = Array.dup
# => OldArray

class Array
    def my_method; "My Method"; end
end
# => nil

[].my_method
# => "My Method"

x = Array.new
# => []

x.my_method
# => "My Method"

### Switch back
Array = OldArray.dup
(irb):9: warning: already initialized constant Array
# => Array

x.my_method
# => "My Method"

(Ok, now why did that work? Maybe "x" is still using the modified Array class?)

[].my_method
# => "My Method"

(Same thing here, it seems)

[1, 2, 3].my_method
# => "My Method"

(Hmmmm, let's try something different)

x = Array.new
# => []

x.my_method
NoMethodError: undefined method `my_method' for []:Array
        from (irb):14

(Ok, so new instances only? Is this weird at all, or is this the way
it's supposed to work?)

I'm asking these questions out of real lack of knowledge, and I REALLY
don't suppose
something should change in order to make this work. I'm just trying to
understand how
Ruby does all this stuff.

Thank you in advance,
Marcelo Alvim.

···

from :0

2

you can't easily undo class changes. better to not make them in the first
place. this will work

harp:~ > cat a.rb
module ProxyClass
   def self.new parent
     Class.new(parent) do
       const_set :PARENT, parent
       instance_methods.each{|m| undef_method m unless m[%r/__/]}
       c = self and define_method(:class){ c }
       def method_missing m, *a, &b
         self.class::PARENT.instance_method(m).bind(self).call(*a, &b)
       end
     end
   end
end
class Class
   def proxy() ProxyClass.new(self) end
end

A = Array.proxy

class A
   def foo() :foo end
end

a = A[ 0, 1, 2 ]

p a.class
p a[0]
p a.first(2)
p a.foo

harp:~ > ruby a.rb
A
0
[0, 1]
:foo

regards.

-a

···

On Tue, 17 Apr 2007, Marcelo Alvim wrote:

Hi,

Well, I'm new to Ruby (I've been working and playing with it for the
last 6 months only), and
I know there's probably another way in which this could work, but
somehow I feel like the
code below should work. Let's see what you guys think about it.

The idea is making a copy of a class object, changing it and then
restoring it back to what it was after playing with the new stuff I
added. It should go somewhat like this:

--
be kind whenever possible... it is always possible.
- the dalai lama