Make Edge Cases Explicit
REFACTORING-MAKE-EDGE-CASES-EXPLICIT
Summary
Name boundary behavior near the branch, calculation, or return that depends on it. This makes policy reviewable and shows when stronger types should prevent invalid states instead.
Rule
Make edge-case behavior explicit in the local control flow.
Why
Boundary values such as empty input, zero sizes, overflow, underflow, duplicates, missing fields, and already-complete states often decide whether a change is correct. When those cases are hidden inside incidental arithmetic, default fallbacks, or distant helpers, reviewers have to infer policy from mechanics.
Naming the edge case near the branch, calculation, or return makes the policy reviewable. It also shows whether the behavior is intentional, accidental, unhandled, or better expressed by a type that cannot represent the invalid state.
Helps
- Makes boundary behavior visible during review.
- Reduces accidental changes to empty, zero, overflow, and already-complete cases.
Limits
Do not add defensive branches for impossible states without first asking whether the type or parser should make the state impossible. Keep rare edge cases local when they matter only to one operation; promote them to a named type, constructor, or state transition when many callers need the same policy.
Agent Instruction
Make edge-case behavior visible near correctness-sensitive branches, calculations, or returns;
prefer stronger types for reusable invariants.Mechanisms
Supported by guard clauses, named local variables, explicit match arms, focused tests for boundary values, and types or constructors that prevent invalid states from entering trusted code.