Welcome to the third lesson of our course, where we explore the concept of Parameter Object to address a common code smell: complex function signatures. Throughout this course, we'll work on eliminating code smells to enhance the readability, maintainability, and scalability of your codebase, with a strong emphasis on Test Driven Development (TDD).

In our previous lessons, we tackled code smells like duplicated code using the Extract Method technique to manage long methods. Today, we'll confront the code smell associated with long parameter lists and introduce the Parameter Object as an effective solution. We'll leverage Swift's strong type system and use XCTest for testing.

Understanding and mastering the TDD cycle — Red, Green, Refactor — will be critical as we work to eliminate code smells in this lesson.

Long parameter lists are considered a code smell because they complicate function signatures, making the code harder to read, maintain, and test. This complexity arises from several issues:

1. Readability: When a function has too many parameters, it's challenging to understand what each parameter represents without referring to the documentation or function implementation. It clutters the function definition and makes the code less intuitive.

2. Maintainability: Modifying a function with a long parameter list becomes cumbersome. Adding or removing parameters can lead to errors in existing function calls across the codebase, increasing the risk of bugs.

3. Error-Prone: It's easy to mix up or misorder parameters, especially when their types are similar. Even with type-checking, logical errors can occur if parameters are passed in the wrong order or are misunderstood.

4. Testing Challenges: Long parameter lists make writing and maintaining tests more difficult, as test cases need to supply many arguments. This complexity can discourage thorough testing and make tests brittle against changes.