Welcome to our lesson on eliminating duplicated code and enhancing maintainability by extracting functions and refactoring magic numbers. In modern software development, writing clean and maintainable code is crucial, and refactoring is a key practice that helps achieve this. In this lesson, we'll focus on how to identify duplicate code segments and restructure them to improve readability and maintainability.

Throughout this course, we will be using Swift, a powerful and intuitive programming language for iOS, macOS, watchOS, and tvOS app development. We will also utilize XCTest, a robust testing framework, to ensure code reliability and facilitate test-driven development (TDD). These tools help write tests efficiently and manage code evolution seamlessly.

This lesson picks up from an existing ShoppingCart example to focus on the Refactor step of the Red-Green-Refactor cycle. Let's dive into identifying and refactoring duplicated code to improve the codebase.

Before we delve into specific "smells," it's important to understand the concept of code smells. Code smells refer to indicators in the code that may suggest deeper problems, such as poorly structured code or potential defects, but aren't bugs themselves. Some common examples include duplicate code, long methods, and magic numbers. These signals often hinder code readability and maintainability and can lead to more significant issues over time.

Refactoring patterns provide structured techniques to address these code smells, improving the overall quality of the codebase while avoiding behavioral changes. By employing these patterns, we can systematically transform problematic sections into cleaner, more efficient code. In this lesson, we'll target duplications by leveraging refactoring patterns, such as extracting functions and refactoring magic numbers, to enhance the clarity and adaptability of our application code. We can rely on our tests to ensure that we don't break any existing functionality!