adaptor_pattern_delegation.rb

class SquarePeg
  attr_reader :width
  
  def initialize(width)
    @width = width
  end
end

class RoundPeg
  attr_reader :radius
  
  def initialize(radius)
    @radius = radius
  end
end

class RoundHole
  attr_reader :radius
  
  def initialize(radius)
    @radius = radius
  end
  
  def peg_fits?(peg)
    peg.radius <= radius
  end
end

class SquarePegAdaptor
  def initialize(square_peg)
    @peg = square_peg
  end
  
  def radius
    Math.sqrt(((@peg.width/2)**2)*2)
  end
end

hole = RoundHole.new(4.0)
4.upto(7) do |i|
  peg = SquarePegAdaptor.new(SquarePeg.new(i.to_f))
  if hole.peg_fits?(peg)
    puts "peg #{peg} fits in hole #{hole}"
  else
    puts "peg #{peg} does not fit in hole"
  end
end

adaptor_pattern_open.rb

class SquarePeg
  attr_reader :width
  
  def initialize(width)
    @width = width
  end
end

class RoundPeg
  attr_reader :radius
  
  def initialize(radius)
    @radius = radius
  end
end

class RoundHole
  attr_reader :radius
  
  def initialize(radius)
    @radius = radius
  end
  
  def peg_fits?(peg)
    peg.radius <= radius
  end
end

class SquarePeg
  def radius
    Math.sqrt(((width/2)**2)*2)
  end
end

hole = RoundHole.new(4.0)
4.upto(7) do |i|
  peg = SquarePeg.new(i.to_f)
  if hole.peg_fits?(peg)
    puts "peg #{peg} fits in hole #{hole}"
  else
    puts "peg #{peg} does not fit in hole"
  end
end

chain_of_responsibility_pattern.rb

class CongaDancer
  attr_reader :next_in_line
  
  def initialize(next_in_line)
    @next_in_line = next_in_line
  end
  
  def shimmy
    puts "shimmy"
    next_in_line.shimmy
  end
  
  def shake
    next_in_line.shake
  end
end

class CongaLeader
  def shimmy
    puts "shimmy!"
  end
  
  def shake
    puts "shake!"
  end
end

line = CongaDancer.new(CongaDancer.new(CongaLeader.new))
line.shimmy
line.shake

decorator_pattern_extend.rb

# Uses extend to dynamically add behaviour

class Coffee
  def cost
    2
  end
end

module Whip
  def cost 
    super + 0.2
  end
end

module Sprinkles
  def cost
    super + 0.3
  end
end

x = Coffee.new
x.extend Sprinkles
x.extend Whip

puts "Coffee with Sprinkles + Whip costs " + x.cost.to_s

decorator_pattern_with.rb

# Uses with to get an even better API syntax

module Whip
  def cost 
    super + 0.2
  end
end

module Sprinkles
  def cost
    super + 0.3
  end
end

class Coffee
  def self.with(*args)
    args.inject(self.new) {|memo, val| memo.extend val}
  end

  def cost
    2
  end
end

x = Coffee.with :sprinkles, :whip
x = Coffee.with Sprinkles, Whip
puts "Coffee with Sprinkles + Whip costs " + x.cost.to_s

decorator_pattern_wrap.rb

class Coffee
  def cost
    2
  end
end

module Decorator
  def initialize(decorated)
    @decorated = decorated
  end

  def method_missing(method, *args)
    args.empty? ? @decorated.send(method) : @decorated.send(method, args)
  end
end

# You can include this into any class you want to act as a decorator.
# You can then use that decorator as if it was the object it is decorating
# By default all messages sent to the decorator are forwarded on to the decorated object.
# You can then decorate the methods you need to extend:

class Milk
  include Decorator

  def cost
    @decorated.cost + 0.4
  end
end

# The real power of decorators lies in the fact that they can act like the objects they are decorating
# You can wrap decorators with other decorators as long as they share the same interface.
# By creating decorators for our different “extras”, we can create coffees using a combination of decorators and get the total cost of the coffee.

class Whip
  include Decorator

  def cost 
    @decorated.cost + 0.2
  end
end

class Sprinkles
  include Decorator

  def cost
    @decorated.cost + 0.3
  end
end

puts "Coffee with Whip costs " + Whip.new(Coffee.new).cost.to_s
puts "Coffee with Milk + Whip + Sprinkes costs " + Sprinkles.new(Whip.new(Milk.new(Coffee.new))).cost.to_s

generic_chain_of_responsibility_pattern.rb

class CongaDancer
  attr_reader :next_in_line
  
  def initialize(next_in_line)
    @next_in_line = next_in_line
  end
  
  def shimmy
    puts "shimmy"
    next_in_line.shimmy
  end
  
  def shake
    next_in_line.shake
  end
end

class CongaLeader < CongaDancer
  def shimmy
    puts "shimmy!"
  end
  
  def shake
    puts "shake!"
  end
end

class CongaDancer
  def method_missing(name, *args)
    puts "don't know how to #{name}, passing it on..."
    next_in_line.__send__(name, *args)
  end
end

class HokieCokieDancer < CongaDancer
  def left
    puts "left kick"
  end
  
  def right
    puts "right kick"
  end
  
  def shake
    puts "shake it all about"
    next_in_line.shake
  end
end

line = CongaLeader.new(HokieCokieDancer.new(CongaDancer.new))
puts "**********************"
line.left
puts "**********************"
line.right
puts "**********************"
line.left
puts "**********************"
line.right
puts "**********************"
line.shake

inheritance_not_decorator_pattern.rb

# Default/Typical approach is to use inheritance

class Coffee
  def cost
    2
  end
end

class MilkCoffee < Coffee
  def cost
    2.4
  end
end

class SweetCoffee < Coffee
  def cost
    2.15
  end
end

class SweetMilkCoffee < Coffee 
  def cost
    2.55
  end
end