Replace Type Code with Polymorphism.

README.md

@@ -74,23 +74,21 @@ possible refactoring patterns to solve it.
 
 ### Refactoring Patterns
 
-  - Extract Class
-  - Extract Method
-  - Move Method
-  - Form Template Method
-  - Inline Class
-  - Introduce Assertion
-  - Introduce Null Object
-  - Introduce Parameter Object
-  - Preserve Whole Object
-  - Move Method
-  - Move Field
-  - Pull Up Method
-  - Rename Method
-  - Replace Array with Object
-  - Replace Method with Method Object
-  - Replace Temp with Query
-  - Replace Temp with Chain
-  - Replace Type Code with Polymorphism
-  - Replace Type Code with Module Extension
-  - Replace Type Code with State/Strategy
+* [x] Extract Class
+* [x] Extract Method
+* [x] Form Template Method
+* [x] Hide Delegate
+* [x] Introduce Assertion
+* [x] Introduce Null Object
+* [x] Separate Query from Modifier
+* [x] Move Field
+* [x] Parameterize Method
+* [x] Preserve Whole Object
+* [x] Pull Up Method
+* [x] Rename Method
+* [x] Replace Array with Object
+* [x] Replace Method with Method Object
+* [x] Replace Temp with Query
+* [-] Replace Type Code with Module Extension
+* [x] Replace Type Code with Polymorphism
+* [-] Replace Type Code with State/Strategy

replace-type-code-with-polymorphism/lib/after.rb

@@ -0,0 +1,33 @@
+class Employee
+  def initialize(type: :regular)
+    @type = type
+  end
+
+  def base_salary
+    500.0
+  end
+
+  def salary
+    base_salary + bonus
+  end
+
+  def self.build(type: :employee)
+    const_get(type.capitalize).new
+  end
+
+  def bonus
+    0
+  end
+end
+
+class Manager < Employee
+  def bonus
+    800
+  end
+end
+
+class Boss < Employee
+  def bonus
+    1500
+  end
+end

replace-type-code-with-polymorphism/lib/before.rb

@@ -0,0 +1,28 @@
+class Employee
+  def initialize(type: :regular)
+    @type = type
+  end
+
+  def base_salary
+    500.0
+  end
+
+  def salary
+    base_salary + bonus
+  end
+
+  def self.build(type: :regular)
+    new type: type
+  end
+
+  private
+
+  def bonus
+    value = case @type
+      when :regular then 0
+      when :boss    then 1500.0
+      when :manager then 800.0
+    end
+  end
+
+end

replace-type-code-with-polymorphism/test/test.rb

@@ -3,3 +3,22 @@
 
 require 'before' if ENV["BEFORE"]
 require 'after' unless ENV["BEFORE"]
+
+describe Employee do
+  describe "a regular one" do
+    it "has a salary" do
+      Employee.build.salary.must_equal 500.0
+    end
+  end
+
+  describe "a boss" do
+    it "has a salary" do
+      Employee.build(type: :boss).salary.must_equal 2000.0
+    end
+  end
+  describe "a manager" do
+    it "has a salary" do
+      Employee.build(type: :manager).salary.must_equal 1300.0
+    end
+  end
+end