From: Eye Matz <matz@...>
Date: 2006-10-03T23:51:47+09:00
Subject: Re: Newbie: Question => How to do this with Classes ?

Jean Helou wrote:
> now for your example :
> class Important
>   def singleton_class
>     #get the singleton class for this instance
>     #A good explanation for the singleton class is available in the 
> pickaxe book
>     #if i remember correctly it's in the duck typing section with a 
> diagram
>     #which makes it all clear.
>     class << self; self; end
>   end
> 
>   #define the class method which will be available as a dsl element.
>   #this is only "syntactic sugar" for your dsl to make it nicer
>   def self.set_this_value_method(value)
>     define_attr_method :this_value_method, value
>   end
> 
>   #Then defines a new method called "name" in the singleton class of
> the instance.
>   #note that here the instance is a class thus it adds a class method
>   def self.define_attr_method(name, value)
>     singleton_class.class_eval do
>      define_method(name) do
>        value
>      end
>   end
> 
> end
> 
> 
> class SemiImportant < Important
>   set_this_value_method :something_or_anything
> end
> 
> now you can call SemiImportant.this_value_method and it will return
> :something_or_anything
> 
> jean

Hi Jean,

Thanks you VERY much for making that example clearer !

One minor error in it, though
>   def singleton_class
>     class << self; self; end
>   end

should be

def self.singleton_class
  class << self; self; end
end

And Yes, I do understand the concept of Singleton classes, just NOT very 
well in Ruby or in Ruby syntax. My problem is really more to do with the 
grammatical logic, ie: when should I use this or that, or how should I 
write this or that to get this or that result.

I haven't found a clear and concise account of that, and therefore I am 
writing stuff like this [ Name are Matz I ] in Ruby, and things don't 
work so well then.

Thank you for your help!


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