Structural Design Patterns

In the real world, you cannot always control the code you work with. You will frequently need to integrate legacy systems, older Objective-C frameworks, or external SDKs into your modern Swift application. The problem arises when these external systems have interfaces that are completely incompatible with your app’s existing architecture. If you force your app to accommodate these legacy interfaces directly—like dealing with NSArray, untyped dictionaries, and completion handlers—your code quickly becomes a tightly coupled, unsafe mess. ...

As your application grows, you often need to add new responsibilities to existing objects. The default approach for many developers is subclassing. However, subclassing is static and applies to an entire class. If you need to combine multiple different behaviors, subclassing leads to a massive, unmaintainable “subclass explosion.” The Decorator pattern (also known as a Wrapper) solves this. It is a structural design pattern that lets you attach new behaviors to objects by placing these objects inside special wrapper objects that contain the behaviors. ...

Modern iOS applications rely on multiple subsystems: networking, local databases, image caching, and third-party SDKs. If your UI or business logic interacts with all of these internal classes directly, your code becomes incredibly dense and difficult to read. The Facade design pattern is a structural pattern that provides a simplified, high-level interface to a complex body of code. It hides the underlying complexity of multiple subsystems behind a single, easy-to-use class. ...