Could you explain the principles of creating readable and maintainable code?

Readable and maintainable code is code that is easy for other developers (or yourself after some time) to understand and modify. Key principles:

• Clear names: variables, functions, and classes should have meaningful names reflecting their purpose.
• Breaking down into functions and modules: each function should perform a single task, modules should be responsible for separate parts of the logic.
• Consistent coding style: adhere to a uniform formatting style, indentation, and conventions.
• Comments where appropriate: write comments where the logic is not obvious, but not excessively.
• Avoid code duplication: use reusable functions and classes.
• Error handling: anticipate and properly handle possible errors.

Example in Swift:

func fetchUserData(userId: String) -> User? {
    // Get user data by ID
    guard let data = database.getUserData(id: userId) else {
        return nil
    }
    return User(data: data)
}

Here, the function has a clear name, performs a single task, and includes a comment for clarification.