From: ara.t.howard@...
Date: 2006-07-13T07:57:58+09:00
Subject: Re: prototype design pattern

On Thu, 13 Jul 2006, Pete wrote:

> Can't imagine how it could be simpler...
>
> class SomeUselessClass
> attr_accessor :a, :b, :c
> def initialize
>  @a, @b, @c = 1, 2, 3
> end
> end
>
> prototype = SomeUselessClass.new
> prototype.a = 7
>
> // create instances from prototype
> o1 = prototype.clone
> o2 = prototype.clone
> o3 = prototype.clone
>
> cheers
> peter

mostly succinctness, but also semantics.  cloning a prototype should not copy
it's instance variables, but rather stamp out a new instance - sort of like a
constructor.  here's a snippet from my latest branch:


     jib:~/eg/ruby/prototype/prototype-0.1.0 > cat samples/d.rb
     require 'prototype'

     proto = prototype{ attributes 'a' => 1, 'b' => 2, 'c' => 3 }

     %w( a b c ).each{|attr| p proto.send(attr)}

     clone = proto.clone
     proto.c = 42

     %w( a b c ).each{|attr| p proto.send(attr)}
     %w( a b c ).each{|attr| p clone.send(attr)}


     jib:~/eg/ruby/prototype/prototype-0.1.0 > ruby -Ilib samples/d.rb
     1
     2
     3
     1
     2
     42
     1
     2
     3


note that this

     proto = Prototype{ attributes 'a' => 1, 'b' => 2, 'c' => 3 }

or, even shorter

     proto = Prototype{ a 1; b 2; c 3 }

are the same, but more, than this

   class SomeUselessClass
     attr_accessor :a, :b, :c
     def initialize
       @a, @b, @c = 1, 2, 3
     end
   end
   prototype = SomeUselessClass.new

actually - to have the literal equiv your code would need to be closer to

   class SomeUselessClass
     ATTRIBUTES = %w( a b c)

     ATTRIBUTES.each do |a|
       attr_accessor a
       alias_method "#{ a }?", "#{ a }"
     end

     def self.attributes() ATTRIBUTES end

     def initialize
       @a, @b, @c = 1, 2, 3
     end
   end

   prototype = SomeUselessClass.new


and actually there's even a bit more..

and it's not even golfing!  ;-)

-a
-- 
suffering increases your inner strength.  also, the wishing for suffering
makes the suffering disappear.
- h.h. the 14th dali lama