swift - How to create enum optional instance -

i leraning swift 3 "the swift programming language (swift 3 beta)". below enum example. in end of example, have written "use init?(rawvalue:) make instance of enumeration raw value". can tell me, how make that. thanks.

enum rank: int {      case ace = 1 // raw value     case two, three, 4 , 5 , six, seven, eight, nine, ten     case jack, queen, king  init?(rawvalue: int) {      self = rawvalue == 1 ? .ace : .jack }      func simpledescription() -> string{          switch self {         case .ace:              return "ace"          case .jack:              return "jack"          case .queen:              return "queen"          case .king:              return "king"          default:              return string(self.rawvalue)         }      } } 

as can see here:

enum rank: int 

"your" rank enums raw value must of type int.

therefore, create new rank element ace value, write:

let ace = rank(rawvalue: 1) 

to create queen write:

let queen = rank(rawvalue: 12) 

notice rank init returns optional. means if give invalid int value, nil in return.

for instance:

let notvalid = rank(rawvalue: 100) //gives nil in return 

hope helps you.