Another amazing functionality Swift gives with enumerations is the ability to incorporate computed properties. A computed property is a property that isn’t directly stored but is instead derived from other stored properties of the enumeration.

Consider this enumeration Patty:

enum Patty: Int {
    case single = 1
    case double
    case triple

    var pattyCountWithExtraPatty: Int {
        return self.rawValue + 1
    }
}

print(Patty.triple.pattyCountWithExtraPatty) // Prints: 4

We assign raw integer values implicitly to each of the cases of Patty. Then we implement the pattyCountWithExtraPatty computed property which returns an integer value equal to one plus what the rawValue is currently set to.

The computed property can return any type of value, and it doesn’t have to be the same as the raw values of the enumeration. In fact, you don’t even have to set raw or associated values for the enumeration cases to implement a computed property in an enumeration.