ruby: Observer Pattern

README.md

Observer Pattern

V1
  name:   Fred Flintstone
  title:  Crane Operator
  salary: 30000
35000

==========================================================================================
V2
Cut a new check for Fred!
His salary is now 35000!

==========================================================================================
V3
Cut a new check for Fred!
His salary is now 35000!
Cut a new check for Fred!
His salary is now 90000!
Send Fred a new tax bill!

==========================================================================================
V4
Cut a new check for Fred!
His salary is now 35000!

==========================================================================================
V5
Cut a new check for Fred!
His salary is now 35000!

==========================================================================================
V6
Cut a new check for Fred!
His salary is now 35000!

==========================================================================================
V7
Cut a new check for Fred!
His salary is now 35000!

==========================================================================================

observer.rb

module Observer
  module V1
    class Employee
      attr_reader :name
      attr_accessor :title, :salary

      def initialize(name, title, salary)
        @name = name
        @title = title
        @salary = salary
      end
    end
  end

  module V2
    class Employee
      attr_reader :name
      attr_accessor :title, :salary

      def initialize(name, title, salary, payroll)
        @name = name
        @title = title
        @salary = salary
        @payroll = payroll
      end

      def salary=(new_salary)
        @salary = new_salary
        payroll.update(self)
      end

      private

      attr_reader :payroll
    end

    class Payroll
      def update(changed_employee)
        puts "Cut a new check for #{changed_employee.name}!"
        puts "His salary is now #{changed_employee.salary}!"
      end
    end
  end

  module V3
    class Employee
      attr_reader :name
      attr_accessor :title, :salary

      def initialize(name, title, salary)
        @name = name
        @title = title
        @salary = salary
        @observers = []
      end

      def salary=(new_salary)
        @salary = new_salary
        notify_observers
      end

      def add_observer(observer)
        observers << observer
      end

      def delete_observer(observer)
        observer.delete(observer)
      end

      private

      attr_reader :observers

      def notify_observers
        observers.each do |observer|
          observer.update(self)
        end
      end
    end

    class TaxMan
      def update(changed_employee)
        puts "Send #{changed_employee.name} a new tax bill!"
      end
    end
  end

  module V4
    class Subject
      def initialize
        @observers = []
      end

      def add_observer(observer)
        observers << observer
      end

      def delete_observer(observer)
        observers.delete(observer)
      end

      private

      attr_reader :observers

      def notify_observers
        observers.each do |observer|
          observer.update(self)
        end
      end
    end

    class Employee < Subject
      attr_reader :name
      attr_accessor :title, :salary

      def initialize(name, title, salary)
        super()

        @name = name
        @title = title
        @salary = salary
      end

      def salary=(new_salary)
        @salary = new_salary
        notify_observers
      end
    end
  end

  module V5
    module Subject
      def initialize
        @observers = []
      end

      def add_observer(observer)
        observers << observer
      end

      def delete_observer(observer)
        observers.delete(observer)
      end

      private

      attr_reader :observers

      def notify_observers
        observers.each do |observer|
          observer.update(self)
        end
      end
    end

    class Employee
      include Subject

      attr_reader :name
      attr_accessor :title, :salary

      def initialize(name, title, salary)
        super()

        @name = name
        @title = title
        @salary = salary
      end

      def salary=(new_salary)
        @salary = new_salary
        notify_observers
      end
    end
  end

  module V6
    require 'observer'

    class Employee
      include Observable

      attr_reader :name
      attr_accessor :title, :salary

      def initialize(name, title, salary)
        @name = name
        @title = title
        @salary = salary
      end

      def salary=(new_salary)
        @salary = new_salary
        changed
        notify_observers(self)
      end
    end
  end

  module V7
    module Subject
      def initialize
        @observers = []
      end

      def add_observer(&observer)
        observers << observer
      end

      def delete_observer(observer)
        observers.delete(observer)
      end

      private

      attr_reader :observers

      def notify_observers
        observers.each do |observer|
          observer.call(self)
        end
      end
    end

    class Employee
      include Subject

      attr_reader :name
      attr_accessor :title, :salary

      def initialize(name, title, salary)
        super()

        @name = name
        @title = title
        @salary = salary
      end

      def salary=(new_salary)
        @salary = new_salary
        notify_observers
      end
    end
  end
end

split = <<-EOF

==========================================================================================
EOF

puts 'V1'

fred = Observer::V1::Employee.new('Fred Flintstone', 'Crane Operator', 30_000)

puts <<-EOF
  name:   #{fred.name}
  title:  #{fred.title}
  salary: #{fred.salary}
EOF

# Give Fred a raise
fred.salary = 35_000

puts fred.salary

puts split
puts 'V2'

payroll = Observer::V2::Payroll.new
fred = Observer::V2::Employee.new('Fred', 'Crane Operator', 30_000, payroll)
fred.salary = 35_000

puts split
puts 'V3'

fred = Observer::V3::Employee.new('Fred', 'Crane Operator', 30_000)

payroll = Observer::V2::Payroll.new
fred.add_observer(payroll)

fred.salary = 35_000

tax_man = Observer::V3::TaxMan.new
fred.add_observer(tax_man)

fred.salary = 90_000

puts split
puts 'V4'

fred = Observer::V4::Employee.new('Fred', 'Crane Operator', 30_000)

payroll = Observer::V2::Payroll.new
fred.add_observer(payroll)

fred.salary = 35_000

puts split
puts 'V5'

fred = Observer::V5::Employee.new('Fred', 'Crane Operator', 30_000)

payroll = Observer::V2::Payroll.new
fred.add_observer(payroll)

fred.salary = 35_000

puts split
puts 'V6'

fred = Observer::V6::Employee.new('Fred', 'Crane Operator', 30_000)

payroll = Observer::V2::Payroll.new
fred.add_observer(payroll)

fred.salary = 35_000

puts split
puts 'V7'

fred = Observer::V7::Employee.new('Fred', 'Crane Operator', 30_000)

fred.add_observer do |changed_employee|
  puts "Cut a new check for #{changed_employee.name}!"
  puts "His salary is now #{changed_employee.salary}!"
end

fred.salary = 35_000

puts split