Methods and computed variables

Say that it is important for us to know whether a person's title relates to a professional qualification that the person holds. Let's add a method to our enum to provide that information:

enum Title: String { 
    case mr = "Mr" 
    case mrs = "Mrs" 
    case mister = "Master" 
    case miss = "Miss" 
    case dr = "Dr" 
    case prof = "Prof" 
    case other // Inferred as "other" 
    func isProfessional() -> Bool { 
        return self == Title.dr || self == Title.prof 
    }
}

For the list of titles that we have defined, Dr and Prof relate to professional qualifications, so we have our method return true if self (the instance of the enum type this method is called on) is equal to the dr case, or equal to the prof case.

This functionality feels more appropriate as a computed property since whether it isProfessional or not is intrinsic to the enum itself, and we don't need to do much work to determine the answer. So, let's change this into a property:

enum Title: String { 
    case mr = "Mr" 
    case mrs = "Mrs" 
    case mister = "Master" 
    case miss = "Miss" 
    case dr = "Dr" 
    case prof = "Prof" 
    case other // Inferred as "other" 
     
    var isProfessional: Bool { 
        return self == Title.dr || self == Title.prof 
    } 
} 

Now, we can determine whether a title is a professional title by accessing the computed property on it:

let loganTitle = Title.mr
let xavierTitle = Title.prof
print(loganTitle.isProfessional) // false
print(xavierTitle.isProfessional) // true

We can't store new information on an enum, but being able to define methods and computed properties that provide extra information about the enum is really powerful.