Suppose I have a base class "Person" that I want to add to a Set (List) and need to therefore conform to Hashable and Equatable:

```
class Person : Equatable, Hashable {
let firstName: String
let lastName: String
var nickname: String?
let dateOfBirth: NSDate
var hashValue: Int {
    if let nickname = nickname {
        return firstName.hashValue ^
               lastName.hashValue ^
               nickname.hashValue ^
               dateOfBirth.hashValue
    } else {
        return firstName.hashValue ^
               lastName.hashValue ^
               dateOfBirth.hashValue
    }

}

init (firstName: String, lastName: String, nickname: String, bornOn dateOfBirth: NSDate) {
    self.firstName = firstName
    self.lastName  = lastName
    self.nickname = nickname
    self.dateOfBirth = dateOfBirth
    }
}

func ==(lhs: Person, rhs: Person) -> Bool {
    return
        lhs.firstName   == rhs.firstName    &&
        lhs.lastName    == rhs.lastName     &&
        lhs.nickname    == rhs.nickname     &&
        lhs.dateOfBirth == rhs.dateOfBirth
}

```

This class has only a single optional property, which makes the dealing with the optional in the creation of the hashvalue fairly reasonable. What if there were 2 or more optional properties? I can see this getting out of hand quite quickly.

How are optional properties generally dealt with when conforming an object to the hashable protocol?