From: Hugh Sasse <hgs@...>
Date: 2005-10-21T19:01:28+09:00
Subject: Re: Reflection, observ(er|able) instance vars?

On Fri, 21 Oct 2005, Trans wrote:

> Use Module, or better yet your own mixin. And just do the class eval
> yourself w/o metaid, it's pretty easy
> 
> module HashAttr
> 
>    def attr_hashing( *arr )
>      attr_reader *arr
>      arr.each do |var|
>        class_eval %{
>          def #{var}(val) ; @var ; end
>        }
>        class_eval %{
>          def #{var}=(val)
>            @var=val
>            @thehash = nil  #reset
>          end
>        }
>      end
>    end
> 
>  end

That's very nice! :-)
> 
> Then do
> 
>   class Wombat
>     extend HashAttr
> 
>     attr_hashing :wom, :bat
>     attr_reader :thehash
> 
>     def initialize
>       @wom = "wom"
>       @bat = "bat"
>       @thehash = nil
>     end
> 
>     def hash
>       puts "hash called"
>       @thehash ||= (@wom.to_s + @bat.to_s).hash
>     end
> 
>     def to_s
>       @wom.inspect + @bat.inspect
>     end
> 
>     # compare
>     def ==( other )
>       hash == other.hash
>     end
>   end 
> 
> HTH,

Yes, that's much simpler than the knots I'd got myself into.  Thank
you.   That will help considerably.

> T.
> 
        Hugh
> 
>