Will 'dateFormatter' evaluate once, like lazy ?
class Birthday {
  private static var dateFormatter: DateFormatter = {
    let formatter = DateFormatter()
    formatter.locale = Locale(identifier: "en_US_POSIX")
    formatter.dateFormat = "d MMMM yyyy"
    return formatter
  }()
  private let date: Date
  init(date: Date) {
    self.date = date
  }
}
asdf