Chapter 3: Replacing in-place mutation with data transformation

In this chapter

  • 3.1　Mutable updates versus immutable transformations
  • 3.2　Two design styles
    • Style A: behavior inside the record
    • Style B: behavior in external functions or services
  • 3.3　Comparing the styles
    • Default recommendation: start with style A
  • 3.4　Adding business-rule validation
    • Throwing exceptions: simple and direct
    • Returning a result type: explicit failure handling
  • 3.5　Transformation pipelines: connecting steps
    • Verifying each step in tests
  • 3.6　Keeping transformations pure
  • 3.7　Cancellation: separating transformation and external coordination
  • 3.8　Common questions
    • “Will creating a new object each time be slow?”
    • “Should I move every method into OrderWorkflow?”
  • 3.9　Chapter review

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