The document discusses the Observer pattern in Ruby. It describes the Observer pattern as allowing one object to notify other "interested" objects when its state changes. It provides an example using the Observable module to implement the pattern. In the example, a Person object notifies an Alert observer whenever send_email is called by calling the notify_observers method, which loops through the observers and calls their gotcha method.

1. Design Patterns in Ruby
Observer Pattern
Copyright 2016. Jyaasa Technologies. All Right Reserved
http://jyaasa.com

2. Neha Suwal
Associate Software Engineer at
Jyaasa Technologies

3. Design Patterns
Design principles are core abstract principles which we are supposed to follow while
designing software architect

4. Observer Pattern:
● one object to inform other ‘interested’ objects when its state changes
The Observable module in the Ruby standard library provides the mechanism necessary
for us to implement this pattern, and it is fairly easy to use.

5. Example:
module Email
extend self
def send(subject, receiver)
mail to: “#{receiver}@example.com”, subject:
“#{subject}”
end
end
class Person
include Email
attr_reader :name
def initialize(name)
@name = name
end
def send_email(subject, receiver)
Email.send(subject, receiver)
end
end

6. bill = Person.new 'Bill'
bill.send_email 'Fishing Trip', 'Fred'

7. class Alert
def gotcha(person)
puts "!!! ALERT: #{person} SENT AN EMAIL !!!"
end
end

8. module Subject
attr_reader :observers
def initialize
@observers = []
end
def add_observer(*observers)
observers.each { |observer| @observers << observer }
end
private
def notify_observers
observers.each { |observer| observer.gotcha(self) }
end
end

9. class Person
include Email, Subject
attr_reader :name
def initialize(name)
# 'super' requires a parentheses because we're calling
# super on the superclass, 'Subject'
super()
@name = name
end
def send_email(subject, receiver)
Email.send(subject, receiver)
notify_observers
end
end

10. alert = Alert.new
bill = Person.new 'Bill'
bill.add_observer alert
bill.send_email 'Fishing Trip', 'Fred'
!!! ALERT: BILL SENT AN EMAIL !!!

11. THANK YOU!