Design Patterns in Ruby | OBSERVER

A behavioral design pattern that aims to create a subscription method to notify multiple objects of events in an observed object.

Problem

Our app has several different subscription plans. Every time a User changes their subscription plan, we want to notify some company teams about that change.

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Solution

Let’s create our user who will have a name and the type of subscription plan.

class User
  attr_reader :name, :plan

  def initialize(name:, plan:)
    @name = name
    @plan = plan
  end
end

john_doe = User.new(name: 'John Doe', plan: 'Standard')

And also create a Team class.

class Team
  attr_reader :name

  def initialize(name)
    @name = name
  end
end

finance = Team.new('Finance')
support = Team.new('Support')

To create an Observer pattern, we need to add several methods to the observed class to be able to manage it from the outside,

class User
  attr_reader :name, :plan, :observers

  def initialize(name:, plan:)
    @name = name
    @plan = plan
    @observers = [] # Store all observers in array
  end
  
  # After plan is changed we want to notify all observers
  def plan=(plan)
    @plan = plan
    
    notify_observers
  end
  
  # Adding observers
  def…