From: James Gray <james@...>
Date: 2008-05-06T21:58:17+09:00
Subject: Re: delegation question, where I want prototype style delegation

On May 6, 2008, at 1:00 AM, Sam Roberts wrote:

> I want to make an object that behaves like another object would, if  
> that
> object had had it's #each method redefined.

What you really want in this case is normal inheritance, so the  
overridden each() method replaces the original.

Then the only thick becomes getting the existing object into an  
equivalent subclass form.  We can use a little Ruby magic to track  
subclasses and do the conversion for us:

class Base
   def self.subclasses
     @subclasses ||= [ ]
   end

   def self.inherited(subclass)
     subclasses << subclass
   end

   def self.subclass(snake_case_name)
     camel_case_name = snake_case_name.gsub(/(?:\A|_)(.)/)  
{ $1.capitalize }
     subclasses.find { |sc| sc.to_s == camel_case_name }
   end

   include Enumerable

   def initialize(ary)
     @ary = Array(ary)
   end

   def each(&block)
     @ary.each(&block)
   end

   def show
     "show: #{to_a.join(", ")}"
   end

   def method_missing(method, *args, &block)
     if method.to_s =~ /\Aas_(\w+)\z/ and (sc = self.class.subclass($1))
       sc.new(@ary)
     else
       super
     end
   end
end

class Negated < Base
   def each
     super { |e| yield -e }
   end
end

class Plus10 < Base
   def each
     super { |e| yield e + 10 }
   end
end

puts "Base:"
b = Base.new(1..3)
puts b.show

puts "Negated:"
puts b.as_negated.show

puts "Plus 10:"
puts b.as_plus_10.show

__END__

Hope that helps.

James Edward Gray II