Optional-Operator-1.swift

class Bird {
    var name: String
    init(name: String) {
        self.name = name
    }
}

class Chicken: Bird {
    let canFly = false
}

class Eagle: Bird {
    let canFly = true
    func fly() {
        print("Eagle is flying.")
    }
}

let chicken = Chicken(name: "Chicky")

// Casting from subclass to parent class by using 'as'
let bird1 = chicken as Bird     // Cast sucessful, bird1 type is Bird
let bird2 = chicken as? Bird    // Warning: Forced cast from 'Chicken' to 'Bird' always succeeds
let bird3 = chicken as! Bird    // Warning: Forced cast from 'Chicken' to 'Bird' always succeeds

// Add chicken into array of type [Bird]
let birds: [Bird] = [chicken]

let chicken1 = birds[0] as Chicken  // Compile error: 'Bird' is not convertible to 'Chicken'
let chicken2 = birds[0] as? Chicken // Cast successful: chicken2 type is Chicken?
let chicken3 = birds[0] as! Chicken // Cast successful: chicken3 type is Chicken

let eagle1 = birds[0] as Eagle  // Compile error: 'Bird' is not convertible to 'Eagle'
let eagle2 = birds[0] as? Eagle // Cast failed: eagle2 is nil
let eagle3 = birds[0] as! Eagle // Cast failed: Trigger runtime error

// Using optional binding to access conditional cast result
if let myChicken = birds[0] as? Chicken {
    print(myChicken.name)
}