shvets / design_patterns_in_ruby

# observer2.rb
 
# Define a one-to-many dependency between objects so that when one object
# changes state, all it's dependents are notified and updated automatically
 
require 'observer'
 
# 1. observer
 
class Observer
  def initialize(name) 
    @name = name
  end
 
  def update(value)
    puts "updated " + @name + ". New value: " + value
  end
end
 
# 2. Observable is imported from 'observer' module
 
# 3. test
 
class Tester
  include Observable
 
  def property= property
    @property = property
  
    changed
    notify_observers(property)
  end
end
 
observer1 = Observer.new("n1")
observer2 = Observer.new("n2")
observer3 = Observer.new("n3")
 
observer4 = Proc.new {}
 
observer4.instance_eval do
  def update(value)
    puts "updated from lambda (update is :#{value})"
  end
end
 
tester = Tester.new
 
tester.add_observer observer1
tester.add_observer observer2
tester.add_observer observer3
tester.add_observer observer4
 
tester.property = 'red'
 
puts '----------'
 
tester.delete_observer observer3
 
tester.property = 'green'