Swift by example enums 

enum Example {
    case A
    case B
    case C
    case D
}
Unlike enums in other languages, the named labels
do not implicitly map to 0, 1.. etc. enum members
are their own values of the type specified by the
enum's name. 

var example = Example.A          // (Enum Value)
Once you assign to an enum value, you can reassign
to another value without respecifying the the enum
name. 

example = .B
Switch statements must be exhaustive or declare
a default case. 

switch example {
case .A:
    print("A")
case .B:
    print("B")                               // B
case .C:
    print("C")
case .D:
    print("D")
}
Enumerations can store values of any type, and
type values can be different for every enum member. 

enum Types {
    case Str(String)
    case Num(Double)
}
A variable can be reassigned a different type of the
enum. 
var a = Types.Str("hello")
a = .Num(1.0)
Associated values can be extracted as part of a switch. 
switch a {
case .Str(let val):
    print(val)
case .Num(let val):
    print(val)                             // 1.0
}

# Raw Values
Enums can prepopulate with "raw" values, similar to other
languages. 
enum Letters: Character {
    case a = "A"
    case b = "B"
    case c = "C"
}
When integers are used for raw values, they
auto-increment if no value is specified. 
enum Numbers: Int {
    case One = 1, Two, Three, Four, Five
}
Access raw values with toRaw 

var five = Numbers.Five
print(five.rawValue)                      // 5
fromRaw tries to find an enum member with a raw value.
An optional is returned. 

var possibleNum = Numbers(rawValue: 2)!
print(possibleNum == Numbers.Two)       // true
TK - type methods and mutating methods