1.swift

enum Planets: String {
	case Mercury
	case Venus
	case Earth
}

// Add protocol to enums that need it
public protocol UsesRawValue {
	var rawValue: String { get }
}

extension Planets: UsesRawValue {}

extension Dictionary where Key: ExpressibleByStringLiteral {
	subscript(key: UsesRawValue) -> Value? {
		get { return self[key.rawValue as! Key] }
		set { self[key.rawValue as! Key] = newValue }
	}
}