Optionals trong Swift

var name: String = "Alice"
// name = nil  // Error!
 
var optionalName: String? = "Alice"
optionalName = nil  // OK

var age: Int? = 25
var email: String? = nil
var height: Double? = 1.75

var name: String? = "Alice"
print(name!)  // Alice
 
name = nil
// print(name!)  // Runtime error: Fatal error!

var name: String? = "Alice"
 
if let unwrappedName = name {
    print("Name: \(unwrappedName)")
} else {
    print("Name is nil")
}

func greet(name: String?) {
    guard let unwrappedName = name else {
        print("No name provided")
        return
    }
    print("Hello, \(unwrappedName)")
}

var name: String? = nil
let displayName = name ?? "Guest"
print(displayName)  // Guest

var name: String? = "Alice"
let length = name?.count  // Optional(5)
 
name = nil
let length2 = name?.count  // nil

var name: String! = "Alice"
print(name)  // Tự động unwrap
 
// Vẫn có thể nil
name = nil
// print(name)  // Crash!

let name: String? = "Alice"
let age: Int? = 25
 
if let unwrappedName = name, let unwrappedAge = age {
    print("\(unwrappedName), \(unwrappedAge) years old")
}