Refactoring Patterns - Hide Delegate

Refactoring Pattern 3: Hide Delegate

Learning Goals

• Explain Hide Delegate & how it promotes encapsulation
• Identify scenarios for which Hide Delegate is the appropriate refactoring pattern to use
• Implement Hide Delegate

Supplies

• You should have a copy of this extraction of Chapter 7.

First 12 minutes individually:

• Briefly read the Hide Delegate section from 181 to 184
• Carefully re-read the code sections on 183 and 184
• Reflect on these key ideas of Hide Delegate:
  • Encapsulation means objects need to know less about other parts of the system
  • Rather than talking through, talk to
  • You can talk to your friends, but don’t talk to your friends’ friends
  • Chains of method calls with different levels of abstraction are a red flag
    • Instead, pass the messages like a bucket brigade
  • The Law of Demeter is not a law and is not about agriculture
• Try refactoring this example scenario (you should already have this cloned) using Hide Delegate. As you encapsulate the use of the delegated object, make sure the linked test still passes
• If you finish early, apply this refactoring pattern to the Enigma examples found under Additional Resources in the main lesson for today
• If you still have more time, apply this refactoring pattern to your current project

Final 3 minutes in your small group:

• Answer the following questions:
  • What is encapsulation?
  • Why would we want to hide delegates?
  • What’s one clear indication that you should implement Hide Delegate?
• Compare solutions