The article distinguishes between illegal states (system states that should never occur) and unwanted states (states that are undesirable but may temporarily exist). It argues that systems must represent unwanted states to handle real-world unpredictability like user errors or network issues, using examples from calendaring software and airline bookings. This distinction helps designers create more robust systems that can gracefully handle edge cases without crashing.
Background
In software and system design, managing state validity is crucial for reliability and correctness. Traditional approaches often focus on preventing invalid states entirely through type systems or constraints.
- Source
- Lobsters
- Published
- Apr 28, 2026 at 11:40 PM
- Score
- 7.0 / 10