Delegation in Ruby with DelegateClass.

setsdelegate.rb

require 'delegate'
class Set2 < DelegateClass(Array)

  attr_accessor :sep
  attr_reader :a
  protected :a

  def initialize(*a)
    @sep = ', '
    @a = a.uniq.sort
    super(@a)
  end

  def to_s
    @a.join(@sep)
  end

  # delegated
  #def length 
  #  @a.length
  #end

  alias cardinal length

  # delegated
  #def include?(x)
  #  @a.include? x
  #end

end

if __FILE__  == $0
  x = Set2.new(1, 2, 3, 3, 4)
  puts "x = {#{x}}"
  puts "x.length = #{x.length}"              # x.length = 4 
  puts "x.cardinal = #{x.cardinal}"          # x.cardinal = 4

  puts "x includes 2 = #{x.include? 2}"      # x includes 2 = true
  puts "x includes 8 = #{x.include? 8}"      # x includes 8 = false
end