From: Rajinder Yadav <devguy.ca@...>
Date: 2009-12-15T20:17:08+09:00
Subject: Re: meta-programming

Brian Candler wrote:
> Rajinder Yadav wrote:
>> How would I declared a, 'class Person' dynamically
> 
> Option 1: since you're using string eval already, you could just do the 
> same.
> 
> eval "class Person; end"
> 
> Option 2:
> 
> Person = Class.new         # superclass is Object
> Person = Class.new(Mammal) # superclass is Mammal
> 
> I find this isn't often done in practice though. A program which doesn't 
> know in advance which classes it has can be a bit too dynamic :-) You 
> would probably register your classes somewhere to be able to find them. 
> In a Hash is one option; under a Module is another, so you can use
> 
>    MyModule.constants
> 
> to find them all.
> 
> You can make your classes anonymous if you don't bind them to a 
> constant:
> 
>    my_klass = Class.new
> 
>> and then add methods and attributes to it?
> 
> As you've done before, using string eval, is one way.
> 
> Another way:
> 
>     Person.class_eval { define_method(:greet) { puts "Hello" } }
> 
> This means that the method is a closure, and can access variables 
> outside (unlike 'def' which starts a fresh scope), and this can be 
> useful sometimes.
> 
> Another way: put the method(s) of interest in module(s), then include 
> the relevant ones.
> 
>     Person.class_eval { include Greeter }
> 
> ActiveRecord is a plentiful source of examples.

Hi Brian,

thanks for the excellent examples and explanation =), I can't stop 
smiling about how beautiful and elegantly simple Ruby make things.

-- 
Kind Regards,
Rajinder Yadav

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