Enumerations aren’t technically one of the three primary collection types offered by Swift (Arrays, Sets, and Dictionaries). However, they do define a set of cases, and you may find yourself in a situation where it is convenient to iterate across all of the cases like you would with a collection. Let’s say that you are making an app where the user can select the season:

enum Season {
    case winter
    case spring
    case summer
    case fall
}

We need to be able to iterate over all the seasons to show them in an array. Since enumerations aren’t able to do this on their own, we need to utilize a protocol. You’ll learn about protocols more in-depth later, but all you need to know now is that protocols define a set of methods and properties that can be adopted by an enumeration.

To iterate over the seasons, we’ll use the CaseIterable protocol. Here’s the syntax:

enum Season: CaseIterable {
    case winter
    case spring
    case summer
    case fall
}

CaseIterable gives us access to a property called allCases that returns an array of case values. We’ll append this property onto Season and iterate over each case with a for loop:

for season in Season.allCases {
    print(season)
}

/* Prints to the console:
winter
spring
summer
fall 
*/