Optionals
Optional Types
Optionals types are declared with a ? after the type name. Optionals either contain a value or nil which represents the absence of a value.
var email: String? = nil
Force Unwrapping Optionals
The ! operator force unwraps an optional. If the underlying value is not nil, it can then be used. If the underlying value is nil, then the program will crash.
var name: String? = "Codey"var email: String? = nilprint("The user's name is \(userName!)") // Prints "The user's name is Codey"print("The user's email is \(userEmail!)") // Crashes!
Optional Binding
Safely unwrap optionals by using an if let statement to bind the optional to a new variable. If the optional is nil, then the code in the else block will run.
var name: String? = "Codey"var email: String? = nilif let name = name {print("The user's name is \(name)")} else {print("No name available")}if let unwrappedEmail = email {print("The user's email is \(unwrappedEmail)")} else {print("No email available")}// Prints:// "The user's name is Codey"// No email available
Multiple Optional Bindings
Multiple optionals can be bound in the same if let statement, separating each binding with “,”. if let statements can also check to see if a boolean expression evaluates to true.
var name: String? = "Codey"if let name = name, let email = email, email.contains("@") {print("Welcome to Codecademy \(name)! Your email address is \(email)")} else {print("Name is nil, email is nil, or the email is invalid")}// Prints "Welcome to Codecademy Codey! Your email address is [email protected]"
Guard Statements
A guard block is another way to write a conditional in Swift. All guard statements must have an else block that exits the current scope if the boolean expression is false. If the guard statement is true, the code below continues executing. Optionals can be bound in a guard block using the guard let syntax.
var name: String? = "Codey"func displayMessageIfValid() {guard let name = name, let email = email, email.contains("@") else {return}print("Welcome \(name)! Your email is \(email)")}displayMessageIfValid()// Prints: "Welcome Codey! Your email is [email protected]"
Nil-Coalescing Operator
The nil-coalescing operator ?? unwraps an optional value and provides a default if the optional is nil.
var email: String? = nilprint("Welcome! Your email is \(email ?? "unknown").")// Prints: "Welcome! Your email is unknown."
Optionals and Functions
Functions can take in optional types and return optional types. A function should return nil when it isn’t able to return a sensible instance of the requested type.
func getFirstInitial(from name: String?) -> String? {return name?.first}
