Simple use of optionals in Swift 5.

Optionals.swift

//
// Simple use of optionals
//

// unwrapping with if let
var nickname: String? = nil

if let unwrap = nickname {
    print("Successfully created user as: \(unwrap).")
} else {
    print("User creation failed.")
}


// unwrapping with guard let
func brand(name: String?) {
    guard let unwrapped = name else {
        print("There is no name!")
        return
    }
    print("My favourite brand is \(unwrapped).")
}
brand(name: nil)     // There is no name!


// nil coalescing
func queue(position: Int) -> String? {
    if position == 1 {
        return "You are next."
    } else {
        return nil
    }
}
let person = queue(position: 5) ?? "You must wait."
print(person)     // You must wait.


// failable initializer
struct User {
    var password: String
    
    init?(password: String) {
        if password.count >= 8 {
            self.password = password
        } else {
            return nil
        }
    }
}
let jack = User(password: "passwrd")
print(jack?.password ?? "Password too short!")     // Password too short!


// typecasting
class Engine { }
class Electric: Engine { }
class Petrol: Engine {
    func makeBrap() {
        print("Brap!")
    }
}
let engines = [Electric(), Petrol(), Electric(), Petrol()]

for engine in engines {
    if let brapMaker = engine as? Petrol {
        brapMaker.makeBrap()
    }
}
// Brap!
// Brap!