Swift Language Getting started with Swift Language Optional Value and Optional enum
Example
Optionals type, which handles the absence of a value. Optionals say either "there is a value, and it equals x" or "there isn't a value at all".
An Optional is a type on its own, actually one of Swift’s new super-powered enums. It has two possible values, None and Some(T), where T is an associated value of the correct data type available in Swift.
Let's have a look at this piece of code for example:
let x: String? = "Hello World"
if let y = x {
print(y)
}
In fact if you add a print(x.dynamicType) statement in the code above you'll see this in the console:
Optional<String>
String? is actually syntactic sugar for Optional, and Optional is a type in its own right.
Here's a simplified version of the header of Optional, which you can see by command-clicking on the word Optional in your code from Xcode:
enum Optional<Wrapped> {
/// The absence of a value.
case none
/// The presence of a value, stored as `Wrapped`.
case some(Wrapped)
}
Optional is actually an enum, defined in relation to a generic type Wrapped. It has two cases: .none to represent the absence of a value, and .some to represent the presence of a value, which is stored as its associated value of type Wrapped.
Let me go through it again: String? is not a String but an Optional<String>.The fact that Optional is a type means that it has its own methods, for example map and flatMap.
