Swift enums, Equatable and Hashable

enum.swift

// Enums with associated values are not equatable...
enum MyEnum {
    case a(number: Int)
    case b
    case c(text: String)
}

// We can define a hash based on the case or the case plus associated value.
extension MyEnum: Hashable {
	public var hashValue: Int {

		switch self {
		case .a(let number):
			return "a \(number)".hashValue

        case .b:
            return "b".hashValue

		case .c(let text):
			return "c \(text)".hashValue
		}
	}

    /*
     Alternative 
	public var hashValue: Int {

		switch self {
		case .a(let number):
			return 0

        case .b:
            return 1

		case .c(let text):
			return 2
        }
	}
    */
}

extension MyEnum: Equatable {
	public static func ==(lhs: MyEnum, rhs: MyEnum) -> Bool {
        return lhs.hashValue == rhs.hashValue
    }
}

let h1 = MyEnum.a(number: 1971).hashValue
let h2 = MyEnum.a(number: 13).hashValue
let h3 = MyEnum.b.hashValue
let h4 = MyEnum.c(text: "bibble").hashValue

var dict: [MyEnum: String] = [
    MyEnum.a(number: 1971): "nineteenseventyone",
    MyEnum.a(number: 13): "thirteen",
    MyEnum.b: "b",
    MyEnum.c(text: "bibble"): "wibble"
]

let equals1 = MyEnum.a(number: 13) == MyEnum.a(number: 13)
let equals2 = MyEnum.a(number: 13) == MyEnum.a(number: 007)
let equals3 = MyEnum.a(number: 13) == MyEnum.b