Habit: look for your heuristics and competing heuristics

Heuristics competing against Favour Composition over Inheritance

• Heuristic: Use inheritance when template pattern fits

• Heuristic: Use inheritance when is-a

• Heuristic: Use inheritance when behaves-like-a

• Heuristic: Use inheritance when and only when there is inheritance in the domain

Heuristics competing about reality

• Heuristic: Don't model reality, evaluate for usefulness...driven by the domain

• Heuristic: immutable in reality => immutable in code

• • invoice - ready, signed off, sent out, does not change anymore

  • Heuristic: when your solution involves breaking&entering, find another solution

Heuristics to help find competing heuristics

• Heuristic: Assume there are multiple possible models

• • core DDD heuristics

(src: Video: Design Heuristics - Mathias Verraes - KanDDDinsky 2018)