From: Robert Klemme <bob.news@...>
Date: 2006-02-02T06:41:32+09:00
Subject: Re: local variable and closure

Sch�le Daniel wrote:
> Hello,
>
> below is one little script that fails at ### <<< line
> the output is
>
> Animal has properties
> Animal will be speakable
> Dog has properties
> Dog will be speakable
> Duck has properties
> Duck will be speakable
> ./dort.rb:16:in `speak': undefined local variable or method `msg' for
> #<Dog:0x401d8da0> (NameError)
>          from ./dort.rb:44
>
> I would think that (passed to function) local variable msg would be
> "closed" in self.class_eval {} closure and therefor be accessable
>
> can someone point out why it doesn't work?
>
> Regards, Daniel
>
>
> #!/usr/bin/env ruby
>
> $prop = {}
>
> def prop
> puts "#{self.name} has properties"
> self.class_eval do
> $prop[self] = []
> end
> end
>
> def speakable(msg)
> puts "#{self.name} will be speakable"
> self.class_eval do
> $prop[self] << "I can speak"
> def speak;msg;end ### <<<
> end
> end
>
> class Animal
> prop
> speakable "..."
> def whatCanIDo;$prop[self.class];end
> def self.whatCanIDo;$prop[self];end
> end
>
> class Dog < Animal
> prop
> speakable "wuff"
> end
>
> class Duck < Animal
> prop
> speakable "quak"
> end
>
> a = Dog.new
> b = Duck.new
>
> puts a.speak, b.speak

Without looking too close at your code: def has special scoping rules.
You better try to use define_method:

def speakable(msg)
  class_eval do
    # ...
    define_method(:speak) msg end
  end
end

HTH

Btw, what are you trying to accomplish?  Somehow I have the feeling that
your code might be more complex than needed.  Especially the use of a
global variable irritates me.

Kind regards

    robert