gistfile1.rb

module Sliceable
  def slice!
    if @sliced
      puts "The #{name} is already sliced!\n"
    else
      @sliced = true
      puts "Done slicing the #{name}.\n"
    end
  end
end

# The singleton module allows us to create singleton classes.
require 'singleton'
class Apple
  include Singleton
  extend Sliceable
end

# A Ruby module makes a more lightweight singleton.
module Persimmon
  extend Sliceable
end

# An object instance can serve as a super lightweight singleton.
Tangelo = Object.new
def Tangelo.name; "Tangelo"; end
Tangelo.extend Sliceable

# Singleton classes allow inheritance. The other alternatives don't allow this.
class Pair < Apple
end

[Apple, Persimmon, Tangelo, Pair].each do |c|
  2.times{ c.slice! }
  begin
    c.new
  rescue NoMethodError
    puts("Unable to call #{c.name}.new\n\n")
  end
end