Improving structure without changing behaviour.
WHAT IT IS
Changing the structure of code while preserving what it does.
WHY IT MATTERS
Without it, code decays with every change, until change becomes impractical.
WHAT IT REQUIRES
Tests.
WHY
Without them you cannot know behaviour was preserved.
WHAT TO DO IF THERE ARE NO TESTS
Write them for the area you are changing, first.
WHAT COMMON REFACTORINGS ARE
Extracting a function or a variable Renaming Inlining something that adds nothing Replacing a conditional chain with polymorphism Moving something to where it belongs Introducing a parameter object
WHEN TO REFACTOR
Continuously, in small steps, as part of normal work.
WHY NOT AS A PROJECT
Large refactoring projects are difficult to justify, are cancelled, and produce long-lived branches.
WHAT THE RULE IS
Leave the code better than you found it, slightly, each time.
WHAT TO AVOID
Refactoring and changing behaviour in the same commit.
WHY
The real change becomes invisible among structural changes.
WHAT TO RUN AFTER EVERY STEP
The tests.
