What is an enum?

Swift version: 5.0

Paul Hudson    @twostraws    March 28th 2019

“Enum” is short for “enumeration”, and it’s a way of letting you use fixed names for special values rather than relying on strings or integers.

For example, if we wanted to track how happy a user was, you could use a number scale where -1 meant unhappy, +1 meant happy, and 0 meant they were in between, but then the onus is on you to remember what those numbers mean. A better idea is to use an enum like this one:

enum Satisfaction {
    case unhappy
    case meh
    case happy
}

Those cases can now be referenced as Satisfaction.happy, so it’s clear what you mean – and internally it’s treated no different from an integer, so it has no performance impact.

We can create a Person struct using that new enum, like this:

struct Person {
    var name: String
    var satisfaction: Satisfaction
}

Because Swift knows the satisfaction property must be a value from the Satisfaction enum we can just specify the case we want to use when creating a value:

let person = Person(name: "Taylor", satisfaction: .happy)

Available from iOS 8.0

Did this solution work for you? Please pass it on!

Tweet

Other people are reading…

• How to check your program state using precondition()
• How to check whether a module is available using canImport()
• What is destructuring?
• What is the autoclosure attribute?
• How to add warnings and errors to your code using #warning and #error

About the Swift Knowledge Base

This is part of the Swift Knowledge Base, a free, searchable collection of solutions for common iOS questions.