Responsibility

Object Oriented Design done right.

José Mota

Ruby and Javascript instructor at Tuts+ for 1.5 years

Code Retreats em Portugal

Objectives

• How OOD is used
  
• How it should be used
• How it helps define responsibilities
  

Typical case for objects

class User
  def buy(product)
    # code that makes the user buy a product
  end
end 

What's wrong in the picture?

Title

class User
  def buy(product)
    # code that makes the user buy a product
  end
end

What does buy do?

• Updates the stock of the product
  
• Deals with a money charge from the user
• Emails a receipt
• Engages a whole process of shipping
  

Solution

Create a new class with the specific

responsibility of handling a purchase.

class User
  def buy(product)
    Purchase.new(user, product).execute
  end
end

class Purchase
  def initialize user, product
    @user = user
    @product = product
  end

  def execute
    update_stock
    charge_user
    deliver_receipt
    engage_shipping
  end
end

Feature change

What to do?

It breaks the code.

Solution

Create a class that handles multiple products.

class PurchaseMany
  def initialize user, products
    @user = user
    @product = products
  end

  def execute
    @products.each do |product|
      Purchase.new(user, product).execute
    end
  endend

Demo