Code smells and refactoring

Refactoring means changing the structure of code without changing what it does. You do it in small steps, with the tests passing after each one. A code smell is a sign that a refactoring might help.

Common smells are a very long function, a long list of parameters, duplicated code, a vague name, deeply nested if statements, or one change that forces edits in many files. Each smell has standard fixes. You can extract part of a function into its own function, rename things, or replace nested conditions with early returns.

You can also group related parameters into a small class. One rule keeps it safe: never refactor and add features in the same step, and run the tests after every change. This is the core of the milestone.