Mastering Type Casting in Swift: is, as?, as!, and as

import Foundation

class Vehicle {
    let wheels: Int
    init(wheels: Int) { self.wheels = wheels }
    func describe() { print("This vehicle has \(wheels) wheels.") }
}

class Car: Vehicle {
    let make: String
    init(make: String, wheels: Int) { self.make = make; super.init(wheels: wheels) }
    override func describe() { print("This is a \(make) car with \(wheels) wheels.") }
}

class Bicycle: Vehicle {
    let type: String
    init(type: String, wheels: Int) { self.type = type; super.init(wheels: wheels) }
    override func describe() { print("This is a \(type) bicycle with \(wheels) wheels.") }
}

let vehicleCollection: [Vehicle] = [
    Car(make: "Toyota", wheels: 4),
    Bicycle(type: "Mountain", wheels: 2),
    Vehicle(wheels: 18),
    Car(make: "Honda", wheels: 4)
]

for vehicle in vehicleCollection {
    if vehicle is Car {
        print("Found a Car!")
    } else if vehicle is Bicycle {
        print("Found a Bicycle!")
    } else {
        print("Found a generic Vehicle.")
    }
}

// Output:
// Found a Car!
// Found a Bicycle!
// Found a generic Vehicle.
// Found a Car!

import Foundation

// ... (Vehicle, Car, Bicycle classes as defined previously)

let vehicleCollection: [Vehicle] = [
    Car(make: "Tesla", wheels: 4),
    Bicycle(type: "Road", wheels: 2),
    Vehicle(wheels: 6)
]

for vehicle in vehicleCollection {
    if let car = vehicle as? Car {
        print("Downcast to Car: \(car.make)")
    } else if let bicycle = vehicle as? Bicycle {
        print("Downcast to Bicycle: \(bicycle.type)")
    } else {
        print("Could not downcast to Car or Bicycle.")
    }
}

// Output:
// Downcast to Car: Tesla
// Downcast to Bicycle: Road
// Could not downcast to Car or Bicycle.

import UIKit // Or Foundation if not using UI elements

class MyCustomCell: UITableViewCell {
    var titleLabel: UILabel = UILabel()
    override init(style: UITableViewCell.CellStyle, reuseIdentifier: String?) {
        super.init(style: style, reuseIdentifier: reuseIdentifier)
        contentView.addSubview(titleLabel)
        // Assume layout constraints are added here
    }
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}

// Example using as! (typical in cellForRowAt; not meant to be run directly)
func dequeueExample() {
    let tableView = UITableView()
    tableView.register(MyCustomCell.self, forCellReuseIdentifier: "MyCustomCellReuseID")
    
    // In a real scenario, this would be within tableView(cellForRowAt:)
    // We are certain a MyCustomCell will be returned because we registered it.
    let cell = tableView.dequeueReusableCell(withIdentifier: "MyCustomCellReuseID", for: IndexPath(row: 0, section: 0)) as! MyCustomCell
    cell.titleLabel.text = "Hello Type Casting!"
    print("Cell title: \(cell.titleLabel.text ?? "")")

    // Uncommenting the following line would cause a crash
    // let faultyCell = Vehicle(wheels: 4) as! Car // Compiler error, but if it were runtime, it'd crash
}

// dequeueExample()

import Foundation

// ... (Vehicle, Car classes as defined previously)

let myCar = Car(make: "Ford", wheels: 4)

// Upcasting to Vehicle is always safe and doesn't require '?' or '!'.
let generalVehicle: Vehicle = myCar as Vehicle
generalVehicle.describe() // Calls Car's overridden describe() method

print(type(of: myCar)) // Car
print(type(of: generalVehicle)) // Car (runtime type is still Car)

// Bridging example (often implicit, but can be explicit)
let nsString: NSString = "Hello Swift" as NSString
let swiftString: String = nsString as String
print(nsString)
print(swiftString)

import Foundation

protocol Printable {
    var name: String { get }
    func printContent()
}

class Document: Printable {
    var name: String
    let content: String
    init(name: String, content: String) { self.name = name; self.content = content }
    func printContent() {
        print("Printing Document '\(name)': \(content)")
    }
}

class Image: Printable {
    var name: String
    let resolution: String
    init(name: String, resolution: String) { self.name = name; self.resolution = resolution }
    func printContent() {
        print("Printing Image '\(name)' at resolution: \(resolution)")
    }
}

class Report {
    let title: String
    init(title: String) { self.title = title }
}

let thingsToPrint: [Any] = [
    Document(name: "Swift Guide", content: "Learn Swift fundamentals."),
    Image(name: "App Icon", resolution: "512x512"),
    Report(title: "Monthly Revenue"),
    Document(name: "Protocol Deep Dive", content: "Advanced Swift protocols.")
]

for item in thingsToPrint {
    if let printableItem = item as? Printable {
        print("Found a printable item: \(printableItem.name)")
        printableItem.printContent()
    } else {
        print("Item \(item) is not printable.")
    }
}

// Output:
// Found a printable item: Swift Guide
// Printing Document 'Swift Guide': Learn Swift fundamentals.
// Found a printable item: App Icon
// Printing Image 'App Icon' at resolution: 512x512
// Item Optional(__lldb_expr_4.Report) is not printable.
// Found a printable item: Protocol Deep Dive
// Printing Document 'Protocol Deep Dive': Advanced Swift protocols.

import Foundation

// Defining a simple struct and class for demonstration
struct User {
    let name: String
}

class Product {
    let id: String
    init(id: String) { self.id = id }
}

let mixedItems: [Any] = [
    "Hello",
    42,
    User(name: "Alice"),
    Product(id: "P123"),
    { (value: Int) -> Int in return value * 2 }
]

for item in mixedItems {
    switch item {
    case let stringValue as String:
        print("Found a String: \(stringValue.uppercased())")
    case let intValue as Int:
        print("Found an Int: \(intValue + 10)")
    case let user as User:
        print("Found a User: \(user.name)")
    case let product as Product:
        print("Found a Product with ID: \(product.id)")
    case let someFunction as (Int) -> Int:
        print("Found a closure: result is \(someFunction(5))")
    default:
        print("Found something else.")
    }
}

// Output:
// Found a String: HELLO
// Found an Int: 52
// Found a User: Alice
// Found a Product with ID: P123
// Found a closure: result is 10