| name | pow10-rule-04-short-functions |
| description | NASA Power of 10 Rule 4 — Functions ≤60 lines (one printed page). Severity: high. |
Rule 4 — Short Functions
Severity: high
Statement
Each function fits on one printed page — hard limit 60 source lines (excluding comments), soft limit 40. Functions exceeding the hard limit must be decomposed or carry a documented waiver.
Rationale
A function that fits on one page can be reviewed and tested as a unit. Longer functions hide bugs by combining responsibilities. Short functions also make refactoring safer and unit testing tractable.
Universal violation patterns
- Single function > 60 SLoC
- Cyclomatic complexity > 10
- Multiple distinct responsibilities in one body (parsing + validating + persisting)
- Deep nesting (> 3 levels of
if/for)
Universal remediation pattern
Extract by responsibility. Each helper takes one phase of the work and returns its output to the caller, which now reads as a sequential pipeline. Each helper is independently testable.
Per-language guidance
When violation is justified
Generated code, large switch dispatchers (consider table-driven instead), state machines. Document with a waiver:
// pow10: allow rule=4 until=YYYY-MM-DD owner=<handle> reason="generated state table"
Citations
