Episode 17 – Component Coupling

Clean Code

Episode 17

This episode talks about how components should depend on each other.

• Overview
  • Acyclic Dependencies Principle
  • Stable Dependencies Principle
  • Stable Abstractions Principle
• The Acyclic Dependencies Principle
  • Cyclic module cause those module to force to release at the same time
  • Solution is either split the component out or use dependency inversion
• The Stable Dependencies Principle
  • Stability is something that is hard to change.
  • A component should depend on something more stable
  • Stability correlates with number of incoming dependency and inversely correlates to number of outgoing dependency.
• The I metrics
  • I metrics = Fan-out / ( Fan-in + Fan-out )
  • All dependency arrow point toward decreasing I.
• The Stable Abstractions Principle
  • Use open-close principle for the module at the bottom of the dependency.
  • The more stable a component, the more abstract it should be.
  • Abstract number = number of abstract classes / number total classes
  • A + I = 1
• Distance
  • D = | A + I | – 1
  • Zone of uselessness is where there many abstraction but nothing using it
  • Zone of pain is there are too many concrete classes depend on each other
  • Distance metric between zone of uselessness and zone of pain
• References