Code guidelines

• Keep it simple!
• Keep functions and classes reasonably short.
• Minimize side effects.
• Avoid force unwrap.
• Minimize usage of implicitly unwrapped optionals. Only IBOutlet and similar.
• Prefer composition over inheritance.
• Prefer immutability.
• Prefer explicit type declarations for instance variables.
• Use readable names.
• If something is difficult to understand, add some documentation.