1.swift

// An enum of some planets
enum Planets: String {
	case Mercury
	case Venus
	case Earth
}

// This extension will allow us to use string enums without
// explicitly calling rawValue to get the string
extension Dictionary where Key: ExpressibleByStringLiteral {
	subscript(key: Planets) -> Value? {
		get { return self[key.rawValue as! Key] }
		set { self[key.rawValue as! Key] = newValue }
	}
}

// Using an example dictionary
var d = [
	"Earth" : "jikyu",
	"Mercury" : "M"
]

// retrieving values using the string enum
d[Planets.Earth] // "jikyu"
d[Planets.Mercury] // "M"

// retrieving values using rawValue
d[Planets.Earth.rawValue] // "jikyu"
d[Planets.Mercury.rawValue] // "M"

// Setting a value using the enum
d[Planets.Venus] = "The goddess of love"
d[Planets.Venus] // "The goddess of love"