Refactoring: Refactorings/Replace Data Value with Object

Simple data items like strings can become complex to the point where they need behaviors. For example. A telephone field might start out as a simple string, but then needs special formatting behaviors, area code extraction, etc. The best way to fix this is to create an object.

Mechanics

1. Create the class for the value. Give it an equivalent to the field in the source class. Add an attribute reader and a constructor that takes the field as an argument.
2. Change the attribute reader in the source class to call the reader in the new class.
3. If the field is mentioned in the source class constructor, assign the field using the constructor of the new class.
4. Change the attribute reader to create a new instance of the new class.
5. Test
6. You may now need to Change Value to Reference on the new object.

Example

Before

class Order
  attr_accessor :customer

  def initialize(customer)
    @customer = customer
  end
end


# Usage

def self.number_of_orders_for(orders, customer)
  orders.select{ |order| order.customer == customer}.size
end

After

class Customer
  attr_reader :name

  def initialize(name)
    @name = name
  end
end

class Order
  def initialize(customer)
    @customer = Customer.new(customer)
  end

  def customer
    @customer.name
  end

  def customer=(value)
    @customer = Customer.new(value)
  end
end