Swift

What is an Interpreter Pattern? The Interpreter Pattern helps implement a simple language and defines a class based representation for its grammar along with an interpreter to interpret its sentences. Source What problems does it solve? The Interpreter Pattern helps solve following problems: Language Interpretation: When you have a language or syntax that needs to be interpreted, such as mathematical expressions, regular expressions, or domain-specific languages (DSLs), the Interpreter Pattern helps in implementing the logic to interpret and execute these expressions. Extensibility: The Interpreter Pattern allows for easy addition of new grammar rules or language constructs without modifying the core interpreter logic. This promotes extensibility, enabling the interpreter to support new features or languages with minimal changes. Separation of Concerns: It separates the grammar definition from the interpretation logic. This separation of concerns makes the codebase modular and easier to maintain. Changes to the grammar or language rules do not affect the interpretation logic, and vice versa. Real-world code example // Define the protocol for the expression protocol Expression { func interpret() -> Int } // Concrete expression for a number class NumberExpression: Expression { private var value: Int init(_ value: Int) { self.value = value } func interpret() -> Int { return value } } // Concrete expression for addition class AdditionExpression: Expression { private var left: Expression private var right: Expression init(_ left: Expression, _ right: Expression) { self.left = left self.right = right } func interpret() -> Int { return left.interpret() + right.interpret() } } // Concrete expression for subtraction class SubtractionExpression: Expression { private var left: Expression private var right: Expression init(_ left: Expression, _ right: Expression) { self.left = left self.right = right } func interpret() -> Int { return left.interpret() - right.interpret() } } // Concrete expression for multiplication class MultiplicationExpression: Expression { private var left: Expression private var right: Expression init(_ left: Expression, _ right: Expression) { self.left = left self.right = right } func interpret() -> Int { return left.interpret() * right.interpret() } } // Concrete expression for division class DivisionExpression: Expression { private var left: Expression private var right: Expression init(_ left: Expression, _ right: Expression) { self.left = left self.right = right } func interpret() -> Int { let divisor = right.interpret() if divisor != 0 { return left.interpret() / divisor } else { // Handle division by zero error fatalError("Division by zero") } } } // Usage let expression = AdditionExpression( MultiplicationExpression(NumberExpression(2), NumberExpression(3)), DivisionExpression(NumberExpression(10), NumberExpression(5)) ) // Interpret the expression let result = expression.interpret() print("Result: \(result)") Thank you for reading! 😊

What is a Flyweight Pattern? The Flyweight Pattern refers to an object that minimizes memory usage by sharing some of its data with other similar objects. Source What problems does it solve? The Flyweight Pattern helps solve following problems: Large Memory Footprint: When dealing with a large number of objects, especially if these objects share a significant amount of common state, traditional object creation can lead to excessive memory consumption. The Flyweight Pattern reduces memory usage by sharing this common state among multiple objects. Performance Overhead: Creating and managing a large number of objects can also introduce performance overhead due to memory allocation, deallocation, and initialization. By reusing shared objects and minimizing the creation of new objects, the Flyweight Pattern can improve performance. Object Creation Cost: Creating new objects can be costly in terms of time and resources, especially if the objects require complex initialization. By reusing existing objects, the Flyweight Pattern reduces the need for creating new objects, thereby reducing object creation costs. Real-world code example // Flyweight protocol defining the interface for shapes protocol Shape { func draw(at point: CGPoint) } // Concrete flyweight class representing a circle class Circle: Shape { private let radius: CGFloat private let fillColor: UIColor init(radius: CGFloat, fillColor: UIColor) { self.radius = radius self.fillColor = fillColor } func draw(at point: CGPoint) { print("Drawing Circle at (\(point.x), \(point.y)) with radius \(radius) and fill color \(fillColor)") // Actual drawing logic would go here } } // Flyweight factory class responsible for creating and managing flyweight objects class ShapeFactory { private var flyweights = [String: Shape]() func getCircle(radius: CGFloat, fillColor: UIColor) -> Shape { let key = "Circle-\(radius)-\(fillColor)" if let existingShape = flyweights[key] { return existingShape } else { let newShape = Circle(radius: radius, fillColor: fillColor) flyweights[key] = newShape return newShape } } } // Client code let shapeFactory = ShapeFactory() // Request for circles with different properties let circle1 = shapeFactory.getCircle(radius: 10, fillColor: .red) let circle2 = shapeFactory.getCircle(radius: 10, fillColor: .red) // Reusing the same circle object let circle3 = shapeFactory.getCircle(radius: 20, fillColor: .blue) // Drawing circles circle1.draw(at: CGPoint(x: 100, y: 100)) circle2.draw(at: CGPoint(x: 200, y: 200)) circle3.draw(at: CGPoint(x: 300, y: 300)) Thank you for reading! 😊

What is a Chain Of Responsibility Pattern? The Chain Of Responsibility Pattern helps create a chain of objects to examine requests. Each object in turn examines a request and either handles it or passes onto the next object in the chain. Source What problems does it solve? The Chain Of Responsibility Pattern (CoR) helps solve following problems: Dynamic Request Handling: It enables dynamic assignment of responsibilities at runtime. Handlers can be added, removed, or reordered without affecting the client’s code. This flexibility allows for easier maintenance and extension of the system. Decoupling Sender and Receiver: In traditional systems, a sender often needs to know the exact receiver of a request, leading to tight coupling between them. The CoR pattern decouples senders from receivers by allowing multiple objects to handle a request without the sender knowing the specific handler. Real-world code example // Protocol defining the handler interface protocol PurchaseHandler { var next: PurchaseHandler? { get set } func handleRequest(amount: Double) } // Concrete handlers class SmallPurchaseHandler: PurchaseHandler { var next: PurchaseHandler? let maxAmount: Double = 100.0 func handleRequest(amount: Double) { if amount <= maxAmount { print("SmallPurchaseHandler: Purchase approved for $\(amount)") } else if let nextHandler = next { print("SmallPurchaseHandler: Passing request to next handler") nextHandler.handleRequest(amount: amount) } else { print("SmallPurchaseHandler: No handler available, purchase rejected") } } } class MediumPurchaseHandler: PurchaseHandler { var next: PurchaseHandler? let maxAmount: Double = 500.0 func handleRequest(amount: Double) { if amount <= maxAmount { print("MediumPurchaseHandler: Purchase approved for $\(amount)") } else if let nextHandler = next { print("MediumPurchaseHandler: Passing request to next handler") nextHandler.handleRequest(amount: amount) } else { print("MediumPurchaseHandler: No handler available, purchase rejected") } } } class LargePurchaseHandler: PurchaseHandler { var next: PurchaseHandler? func handleRequest(amount: Double) { print("LargePurchaseHandler: Purchase approved for $\(amount)") } } // Usage func main() { let smallHandler = SmallPurchaseHandler() let mediumHandler = MediumPurchaseHandler() let largeHandler = LargePurchaseHandler() // Connecting handlers into a chain smallHandler.next = mediumHandler mediumHandler.next = largeHandler smallHandler.handleRequest(amount: 50.0) smallHandler.handleRequest(amount: 200.0) smallHandler.handleRequest(amount: 1000.0) } Thank you for reading! 😊

What is a State Pattern? The State Pattern allows an object to alter its behavior when its internal state changes. The object will appear to change its class. Source What problems does it solve? Complex conditional logic: When an object’s behavior depends on its internal state, it often leads to complex conditional statements. The State pattern simplifies this by encapsulating each state and its behavior in separate classes, making the code more readable and maintainable. State-specific behavior: Objects often need to change their behavior based on their state. The State pattern allows objects to delegate behavior to state objects, which can vary independently. This promotes better encapsulation and separation of concerns. Adding new states: When new states need to be added, the State pattern makes it easier to extend the functionality without modifying existing code. New states can be added by creating new state classes and integrating them into the existing context, without changing the context class itself. Real-world code example // Define the VendingMachine protocol protocol VendingMachineState { func insertCoin() func dispenseItem() } // Define concrete states class NoCoinState: VendingMachineState { private let vendingMachine: VendingMachine init(vendingMachine: VendingMachine) { self.vendingMachine = vendingMachine } func insertCoin() { print("Coin inserted") // Transition to the HasCoinState vendingMachine.changeState(newState: vendingMachine.hasCoinState) } func dispenseItem() { print("Please insert a coin first") } } class HasCoinState: VendingMachineState { private let vendingMachine: VendingMachine init(vendingMachine: VendingMachine) { self.vendingMachine = vendingMachine } func insertCoin() { print("Coin already inserted") } func dispenseItem() { if vendingMachine.inventoryCount > 0 { print("Item dispensed") vendingMachine.decreaseInventory() // Transition to the NoCoinState vendingMachine.changeState(newState: vendingMachine.noCoinState) } else { print("Out of stock") } } } // Define the VendingMachine class class VendingMachine { var inventoryCount: Int = 5 var currentState: VendingMachineState! var noCoinState: VendingMachineState! var hasCoinState: VendingMachineState! init() { noCoinState = NoCoinState(vendingMachine: self) hasCoinState = HasCoinState(vendingMachine: self) currentState = noCoinState } func changeState(newState: VendingMachineState) { currentState = newState } func insertCoin() { currentState.insertCoin() } func dispenseItem() { currentState.dispenseItem() } func decreaseInventory() { inventoryCount -= 1 } } // Usage let vendingMachine = VendingMachine() vendingMachine.dispenseItem() vendingMachine.insertCoin() vendingMachine.insertCoin() vendingMachine.dispenseItem() vendingMachine.dispenseItem() Thank you for reading! ...

What is a Dependency Inversion Principle? The Dependency Inversion Principle means that high-level modules should not depend on low-level modules. Source Source What problems does it solve? The Dependency Inversion Principle (DIP) helps solve: Rigidity Fragility Immobility problems Real-world code example Violation of DIP // High-level module directly depending on low-level modules class MessageService { func sendMessageViaEmail(message: String) { let emailSender = EmailSender() emailSender.sendMessage(message: message) } func sendMessageViaSMS(message: String) { let smsSender = SMSSender() smsSender.sendMessage(message: message) } func sendMessageViaPushNotification(message: String) { let pushNotificationSender = PushNotificationSender() pushNotificationSender.sendMessage(message: message) } } Adhering to DIP // Protocol defining the interface for sending messages protocol MessageSender { func sendMessage(message: String) } // High-level module depending on abstraction (MessageSender protocol) class MessageService { private let messageSender: MessageSender init(messageSender: MessageSender) { self.messageSender = messageSender } func sendMessage(message: String) { messageSender.sendMessage(message: message) } } // Concrete implementations of MessageSender protocol for different channels class EmailSender: MessageSender { func sendMessage(message: String) { print("Sending email: \(message)") } } class SMSSender: MessageSender { func sendMessage(message: String) { print("Sending SMS: \(message)") } } class PushNotificationSender: MessageSender { func sendMessage(message: String) { print("Sending push notification: \(message)") } } // Example usage let emailSender = EmailSender() let smsSender = SMSSender() let pushNotificationSender = PushNotificationSender() let emailService = MessageService(messageSender: emailSender) let smsService = MessageService(messageSender: smsSender) let pushNotificationService = MessageService(messageSender: pushNotificationSender) emailService.sendMessage(message: "Hello via email") smsService.sendMessage(message: "Hello via SMS") pushNotificationService.sendMessage(message: "Hello via push notification") Thank you for reading! 😊