From: "Jesús Gabriel y Galán" <jgabrielygalan@...>
Date: 2009-12-15T19:49:35+09:00
Subject: Re: meta-programming

On Tue, Dec 15, 2009 at 9:32 AM, Rajinder Yadav <devguy.ca@gmail.com> wrote:
> I am just starting to expand my Ruby knowledge into the area of
> meta-programming.
>
> I want to be able to create a class dynamically. Lets call it, class Person,
> and then I want to add methods to it dynamically.
>
> From a static point I have managed to compile the following example:
>
> class Person
>   def self.extend_me
>   class_eval "def greet; puts 'hello'; end"
>   instance_eval "def name; puts 'Person'; end"
>   end
> end
>
> Person.extend_me
>
> Person.respond_to? :greet
> Person.respond_to? :name
>
> puts Person.name
> p = Person.new
> puts p.greet
>
>
> How would I declared a, 'class Person' dynamically and then add methods and
> attributes to it? Can someone point me to good documentation on this or show
> me some simple code example?

If you want to define the class dynamically, take a look at Class.new.
This creates an anonymous class that you can assign to a constant
directly or with const_set.
To define methods I would use define_method. Adding attributes is done
adding methods that set and get the attributes:

irb(main):042:0> C = Class.new do
irb(main):043:1* def self.add_method(name, &blk)
irb(main):044:2> define_method(name, &blk)
irb(main):045:2> end
irb(main):046:1> end
=> C

irb(main):051:0> C.add_method(:name) {@name}
=> #<Proc:0xb7cb9de8@(irb):51>
irb(main):052:0> C.add_method(:name=) {|value| @name = value}
=> #<Proc:0xb7cb3bf0@(irb):52>
irb(main):053:0> c = C.new
=> #<C:0xb7cb16d4>
irb(main):054:0> c.name=3
=> 3
irb(main):055:0> c.name
=> 3

Hope this helps,

Jesus.