[Swift] Enums with rawValue automatically receive an initializer

Enums with rawValue automatically get an initializer defined

I didn't know this until recently. It is clearly stated on swift.org.

Initializing from a Raw Value

If you define an enumeration with a raw-value type, the enumeration automatically receives an initializer that takes a value of the raw value’s type (as a parameter called rawValue) and returns either an enumeration case or nil. You can use this initializer to try to create a new instance of the enumeration.

https://docs.swift.org/swift-book/LanguageGuide/Enumerations.html

Let's verify the behavior in practice

enum Drink: String {
    case coffee
    case tea
}

print(Drink(rawValue: "coffee") ?? "Undefined") // coffee
print(Drink(rawValue: "tea") ?? "Undefined") // tea
print(Drink(rawValue: "hoge") ?? "Undefined") // Undefined

It seems an initializer like the one below is defined automatically.

enum Drink: String {
    case coffee
    case tea
    
    // This is automatically defined
    init?(rawValue: String) {
        switch rawValue {
        case Drink.coffee.rawValue:
            self = .coffee
        case Drink.tea.rawValue:
            self = .tea
        default:
            return nil
        }
    }
}

Honestly, I think there are limited use cases for this, as most scenarios can be handled by extending the enum definition.

It also feels a bit cumbersome to use because you must account for the fact that the initializer returns nil if there is no matching rawValue.

• References
  • Enumerations - docs.swift.org
  • Initializer init(rawValue:)- Apple Developer Documentation

That's all.