Advanced and Practical Enum usage in Swift

Enum values

released Fri, 01 Mar 2019
Swift Version 5.0

Enum values

Sometimes may want to have a value assigned to each enum case. This is useful if the enum itself indeed relates to something which can be expressed in a different type. C allows you to assign numbers to enum cases. Swift gives you much more flexibility here:

// A pretty useless enum

enum Binary {

   case zero = 0

   case one = 1


// You can also map to strings

enum House: String {

     case baratheon = \"Ours is the Fury\"

     case greyjoy = \"We Do Not Sow\"

     case martell = \"Unbowed, Unbent, Unbroken\"

     case stark = \"Winter is Coming\"

     case tully = \"Family, Duty, Honor\"

     case tyrell = \"Growing Strong\"


// Or to floating point (also note the fancy unicode in enum cases)

enum Constants: Double {

     case π = 3.14159

     case e = 2.71828

     case φ = 1.61803398874

     case λ = 1.30357


For String and Int types, you can even omit the values and the Swift compiler will do the right thing:

// mercury = 1, venus = 2, ... neptune = 8

enum Planet: Int {

     case mercury = 1, venus, earth, mars, jupiter, saturn, uranus, neptune


// north = \"north\", ... west = \"west\"

enum CompassPoint: String {

     case north, south, east, west


Swift supports the following types for the value of an enum:

  • Integer
  • Floating Point
  • String
  • Boolean

You can support more types by implementing a specific protocol.

If you want to access the values, you can do so with the rawValue property:

let bestHouse = House.stark


// prints \"Winter is coming\"

However, there may also be a situation where you want to construct an enum case from an existing raw value. In that case, there's a special initializer for enums:

enum Movement: Int {

     case left = 0

     case right = 1

     case top = 2

     case bottom = 3


// creates a movement.Right case, as the raw value for that is 1

let rightMovement = Movement(rawValue: 1)

If you use the rawValue initializer, keep in mind that it is a failable initializer, i.e. you get back an Optional, as the value you're using may not map to any case at all, say if you were to write Movement(rawValue: 42).