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Types that conform to the CaseIterable protocol are typically enumerations without associated values. When using a CaseIterable type, you can access a collection of all of the type's cases by using the type's allCases property.

For example, the CompassDirection enumeration declared in this example conforms to CaseIterable. You access the number of cases and the cases themselves through CompassDirection.allCases.

enum CompassDirection: CaseIterable {
    case north, south, east, west
}
 
print("There are \(CompassDirection.allCases.count) directions.")
// Prints "There are 4 directions."
let caseList = CompassDirection.allCases
                               .map({ "\($0)" })
                               .joined(separator: ", ")
// caseList == "north, south, east, west"

Conforming to the CaseIterable Protocol

The compiler can automatically provide an implementation of the CaseIterable requirements for any enumeration without associated values or @available attributes on its cases. The synthesized allCases collection provides the cases in order of their declaration.

You can take advantage of this compiler support when defining your own custom enumeration by declaring conformance to CaseIterable in the enumeration's original declaration. The CompassDirection example above demonstrates this automatic implementation.