With some forms of information, we know all of the possible values that can exist. Let’s say you’re building a transportation app. Users can either travel by truck, plane, or boat.

We could just use a String to store that information:

var myRide = "truck"

But that could let us assign myRide to something that’s not a valid ride type:

myRide = "winged monkeys"

That’d be pretty confusing for a user to see! Fortunately, Swift allows us to restrict the possible values that a variable could be.

An enumeration, often shortened to enum (pronounced ee-num), is a way to define your own group of related values and work with them in a type-safe manner. With the enum below, we’ll always know which vehicles are valid:

enum Vehicle {
    case airplane
    case boat
    case truck
}