Observable

A really small and simple implementation of the Observer Pattern in Ruby

To use, include Observable in to any class.

Author: Greg Bell Version: 1.0

1. CREATE AN OBSERVABLE ATTR_ACCESSOR

To create an observable attr_accessor so that other classes can be notified when it changes:

class Employee
  include Observable

  attr_accessor :salary
  observable :salary

end

2. CREATE A CUSTOM OBSERVABLE

To create a custom observable notification:

class Employee
  include Observable

  observable :salary_changed
  
  def update_salary(new_salary)
    
    # update logic code
    
    # Then notify any observers passing it an event hash
    # This will passs the event hash on to any classes who registered
    # to observe this class observable
    notify :salary_changed, { :employee => self}
  end

end

3. REGISTER FOR UPDATES

To register for updates to an observable class:

class HR
  include Observable
  
  # Create an observer and pass the logic to a class method
  observe Employee, :salary , :employee_salary_updated
  
  def self.employee_salary_updated(event)
    puts "#{self} got employee salary updated with #{event.inspect}"
  end

  # OR (these would both create the same results)
  
  # Create an observer and put logic in a block
  observe Employee, :salary do |event|
    puts "#{self} got employee salary updated with #{event.inspect}"
  end
  
end

To register for updates to only ONE observable instance:

# Employee has setup an observable called :salary
employee = Employee.new("Bob")

employee.observe :salary do |event|
	HR.employee_salary_updated(event)
end

4. CREATE ANONYMOUS OBSERVABLES

To create observables that are not associated with any class:

Observable.create :system_message

Observable.observe :system_message do |event|
  puts "Received system message: #{event.inspect}"
end

class Anon
  Observable.observe :system_message do |event|
    puts "Received  inside anon system message: #{event.inspect}"
  end
end

Observable.notify(:system_message, { :message => 'APP STARTED'})

Observable.observe Employee, :salary do |event|
  puts "Anonomously observing employee salary"
end

5. VIEW ALL AVAILABLE OBSERVABLES

You can view all currently observables by calling Observable.all_observables