Design Patterns the Ruby way: strategy

design_patterns_strategy.rb

####### STRATEGY PATTERN #############

### way #1
## The following code implements the strategy pattern in the traditional
## manner, i.e. with a separate class for each strategy (xxxPayment),
## which is then passed in the constructor of the Context class (in
## this case the Purchase class).  The Context then selects a strategy
## at construction time and delegates its stragegy method (i.e. pay) to
## the strategy object


# this abstract base class is un-necessary in Ruby
# class	PaymentStrategy
# 	def pay(sum)
# 		raise "can't call that!"
# 	end
# end


class PayPalPayment #< PaymentStrategy
	def pay(sum)
		puts ".....paying $#{sum} by PayPal"
	end
end

class WorldPayPayment #< PaymentStrategy
	def pay(sum)
		puts ".....paying $#{sum} by WorldPay"
	end
end

class BitcoinPayment #< PaymentStrategy
	def pay(sum)
		puts ".....paying $#{sum} by Bitcoin"
	end
end


class Purchase
	attr_reader :items, :sum
	attr_accessor :payment_method

	def initialize(items, payment_method)
		@payment_method = payment_method
		@sum = 0
		items.each do |item, value|
			@sum += value
		end
	end

	def pay
		payment_method.pay(@sum)
	end
end

puts "####### way 1"
purchase = Purchase.new({cd_Wild_Beasts: 5.2, baseball_cap: 8.5  }, WorldPayPayment.new)
purchase.pay


### way #2
## This is the re-work of the pattern using code blocks (a.k.a lambdas)
## to dynamically define our strategy. We have no more need of Strategy
## objects, as we create our strategy dynamically in a code block, when
## we create the Purchase object. This is a much more flexible and scalable
## way of implementing the Strategy pattern.

class Purchase
	attr_reader :items, :sum
	attr_accessor :payment_method

	def initialize(items, &payment_method)
		@payment_method = payment_method
		@sum = 0
		items.each do |item, value|
			@sum += value
		end
	end

	def pay
		payment_method.call(@sum)
	end
end

puts "####### way 2"
purchase = Purchase.new({cd_Wild_Beasts: 5.2, baseball_cap: 8.5  }) {|sum| puts ".....paying $#{sum} by WorldPay"}
purchase.pay