gistfile1.rb

# based on http://www.ruby-doc.org/stdlib/libdoc/delegate/rdoc/index.html
require 'delegate'

class SimpleDelegator < Delegator
  def initialize(obj)
    super             # pass obj to Delegator constructor, required
    @_sd_obj = obj    # store obj for future use
  end

  def __getobj__
    @_sd_obj          # return object we are delegating to, required
  end

  def __setobj__(obj)
    @_sd_obj = obj    # change delegation object, a feature we're providing
  end
end

proxy_object = SimpleDelegator.new []

proxy_object.push 'first', 'second'
p proxy_object.size # => 2
p proxy_object # => ["first", "second"]

proxy_object.__setobj__ 'hey'
p proxy_object # => "hey"