Refactor

When to refactor

• Function is over 50 lines
• Same pattern appears 3+ times
• You need a comment to explain what code does (the code should say it)
• Changing one thing requires changing many files
• Tests are hard to write for this code

Process

1. Ensure tests exist — never refactor without a safety net
2. Identify the smell — name what's wrong (duplication, coupling, complexity)
3. Apply one transformation — extract function, rename, inline, split
4. Run tests — verify nothing broke
5. Repeat — one small change at a time, never big-bang refactor

Common refactors

• Extract function — pull a named chunk out of a long function
• Rename — make names match what code actually does
• Inline — remove unnecessary abstraction that adds indirection without value
• Split module — break a file doing 3 things into 3 files doing 1 thing each
• Replace conditional with polymorphism — when if/else chains map to types

Rules

• Refactor OR add features. Never both in the same commit.
• The behavior must not change. Refactoring is restructuring, not rewriting.
• If you're not sure the tests cover it, don't refactor it.
• Three similar lines is better than a premature abstraction.