Design Patterns · Middle · Question 51 of 75

How does Parallel Change (expand/contract) help change a widely used function signature?

✓Correct answer: Add the new version alongside the old one, migrate callers gradually, then remove the old version
2Change the signature and fix all callers in one huge commit
3Keep both versions forever

Explanation

Each step is small and deployable. It also works for API fields and database columns.

Further reading

Martin Fowler: Parallel Change ↗

Test yourself

Take the Design Patterns · Middle quiz: questions and options are shuffled, and you get a review of your mistakes at the end.