Introducing design patterns in Swift provides a structured approach to solving common software design problems, improving code maintainability, scalability, and readability. Here’s an overview of some commonly used design patterns in Swift:

1. Model-View-Controller (MVC):
   • MVC separates an application into three interconnected components: Model (data and business logic), View (UI elements), and Controller (mediator between model and view).
   • Swift’s UIKit framework commonly uses MVC for structuring iOS applications.
2. Singleton:
   • Singleton ensures that a class has only one instance globally accessible throughout the application.
   • It is useful for managing shared resources such as database connections, logging, or configuration settings.

class Singleton {
    static let shared = Singleton()
    private init() {}
}

3. Factory:
   • Factory pattern provides an interface for creating objects without specifying their concrete classes.
   • It allows for decoupling of object creation from object usage.

protocol Product {
    func use()
}

class ConcreteProduct: Product {
    func use() {
        print("Using concrete product")
    }
}

class Factory {
    func createProduct() -> Product {
        return ConcreteProduct()
    }
}

4. Observer:
   • Observer pattern defines a one-to-many dependency between objects, where the state of one object (the subject) changes, all its dependents (observers) are notified and updated automatically.
   • It’s commonly used for implementing event handling and data binding.

protocol Observer: AnyObject {
    func update()
}

class Subject {
    private var observers = [Observer]()
    
    func addObserver(_ observer: Observer) {
        observers.append(observer)
    }
    
    func notifyObservers() {
        observers.forEach { $0.update() }
    }
}

5. Decorator:
   • Decorator pattern allows behavior to be added to individual objects dynamically, without affecting the behavior of other objects from the same class.
   • It’s useful for extending the functionality of objects at runtime.

protocol Component {
    func operation()
}

class ConcreteComponent: Component {
    func operation() {
        print("Concrete component operation")
    }
}

class Decorator: Component {
    private let component: Component
    
    init(component: Component) {
        self.component = component
    }
    
    func operation() {
        component.operation()
    }
}

6. Facade:
   • Facade pattern provides a simplified interface to a complex system, hiding its implementation details behind a single interface.
   • It’s commonly used to decouple clients from subsystems and provide a unified interface.

class SubsystemA {
    func operationA() {
        print("Subsystem A operation")
    }
}

class SubsystemB {
    func operationB() {
        print("Subsystem B operation")
    }
}

class Facade {
    private let subsystemA = SubsystemA()
    private let subsystemB = SubsystemB()
    
    func operation() {
        subsystemA.operationA()
        subsystemB.operationB()
    }
}

These are just a few examples of design patterns commonly used in Swift development. Each pattern addresses specific software design problems and provides a reusable solution that can be applied across different projects. Understanding and applying these patterns can significantly improve the structure, maintainability, and flexibility of your Swift codebase.