From: dblack@...
Date: 2007-08-02T21:24:53+09:00
Subject: Re: defining methods dynamically?

Hi --

On Thu, 2 Aug 2007, Wayne E. Seguin wrote:

> On Aug 01, 2007, at 21:49 , dblack@rubypal.com wrote:
>> <snip>
>> There's actually no other way to do it :-)  But I think what you're
>> looking for is #define_method, which lets you define methods with
>> dynamically-determined names and also gives you a way to flatten the
>> variable scope of a method definition.
>> <snip>
>
> David,
>
> I do not follow what you mean by "flatten the variable scope of a method 
> definition".
> Could you please explain what this means a bit?

Sure.  Let's say you want to do:

   a = 1
   class C
     def show_a
       a          # won't work
     end
   end

The definition of a won't make it into the scope of the method
definition #show_a, because both the class keyword and the def keyword
start a new local scope.

However, class_eval and define_method are both permeable, as to scope.
So you can do:

   a = 1
   class C; end
   C.class_eval { define_method(:show_a) { a } }

   C.new.show_a    # 1

The a inside the block given to define_method is the same a that I
defined in the first line.  That's what I mean by flattening the
variable scope.


David

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