tonytvo/introduce-indirection-layer

practice introduce indirection layer

Introduce the indirection layer

• when refactoring, we often end up in situation where single change causing cascading effects of changes and we retreat in our corner and cry, and recently, I have learned a good trick from J.B. Rainberger to introduce indirection layer to help us making small steps incrementally
• X minutes do
  • It seems like OrderLines is a good home (domain concept) for Order.lines field, once you extract Order.lines into OrderLines, we could see a whole bunch of behavior should belong into OrderLines as well
  • Setup
  • checkout https://github.com/tonytvo/introduce-indirection-layer
  • run tests, see them pass
  • extract lines logic in class Order into methods
    • Extract a method isEmpty() to check if the lines is empty
      • 
      • introduce parameter lines
        • 
    • Extract a method asList() to return the list of OrderLine
      • 
      • introduce parameter lines
    • Extract a method incrementItemQuantity(ItemAdded)
      • 
      • introduce parameter lines
  • move lines into parameter object OrderLines
    • introduce lines into parameter objects for asList
      • 
      • move asList method into OrderLines
        • 
    • introduce lines into existing parameter objects for isEmpty
      • 
      • move method into OrderLines
    • introduce lines into existing parameter objects for incrementItemQuantity(ItemAdded)
      • move method into OrderLines
    • introduce orderLines field for new OrderLines(lines)
      • 
    • inline lines field
      • 

References

• https://github.com/codecop/dependency-breaking-katas
• https://tonytvo.github.io/what-simple-way-share-learn-refactor/
• https://github.com/tomphp/event-sourcing-example