From: "T. Onoma" <transami@...>
Date: 2003-11-28T09:38:46+09:00
Subject: Re: Controlled block variables

On Wednesday 26 November 2003 12:05 pm, Pit Capitain wrote:
> maybe you can make use of "define_method" as in
>
>    class X
>      def self.add_method name, value
>        eval "define_method name, proc{value}"
>      end
>    end
>
>    X.add_method :array, [1, 2, 3]
>    X.add_method :hash, {1=>"A", 2=>"B"}
>
>    x = X.new
>
>    p x.array  # => [1, 2, 3]
>    p x.hash   # => {1=>"A", 2=>"B"}

I'll respond here to keep core as prestine as some seem to want it to be. 
Which is fine but indicates to me that we could use a second list for such 
things. Anyway.

Sorry I let this slip by, I wanted to think on it more. And though I have, I 
must admit I'm not quite seeing it --quite possibly my small brain just isn't 
cutting it :-) But perhaps too, there's a communication disconnect. So let me 
lay down the core problem and you show me how your solution solves it. That 
should tell us if were on the same page.
  
  a = [1,2,3]
  class_eval {
    def ameth
      p a
    end
  }

So the problem is, a will be eval'd as nil, since it is outside of def. To 
overcome I must convert a to a literal and stick it in a string.

  a = [1,2,3]
  a = "[#{a.join(',')}]"
  class_eval %Q{
    def ameth
      p #{a}
    end
  }

So how does you solution deal with this problem? 

For comparison I will point out Ryan's solution. Ryan created an object pool 
that has a global scope, then created a special method in the Object class 
that adds any object to the pool, so one then does something like:

  a = [1,2,3]
  a.to_pool
  class_eval {
    def ameth
      p Pool.a
    end
  }

Of course, there is also the solution:

  a = [1,2,3]
  $a = a
  class_eval {
    def ameth
      p $a
    end
  }

While I like Ryan's solutions b/c it just seems like a useful thing to have an 
object pool handy without resorting to global variables, one can easily say 
these are hacks. And for the problem at hand there isn't actually a solution 
that isn't. But it is certainly interesting to see who can come up with the 
best one.

-t0