枚举 – 如何使枚举符合Swift中的协议？

Swift文档说，类，结构和枚举都可以符合协议，我可以达到它们都符合的点。但我不能让枚举的行为很像类和结构的例子：

protocol ExampleProtocol {
    var simpleDescription: String { get set }
    mutating func adjust()
}

class SimpleClass: ExampleProtocol {
    var simpleDescription: String = "A very simple class."
    var anotherProperty: Int = 69105

    func adjust() {
        simpleDescription += " Now 100% adjusted."
    }
}

var a = SimpleClass()
a.adjust()
let aDescription = a.simpleDescription

struct SimpleStructure: ExampleProtocol {
    var simpleDescription: String = "A simple structure"

    mutating func adjust() {
        simpleDescription += " (adjusted)"
    }
}

var b = SimpleStructure()
b.adjust()
let bDescription = b.simpleDescription

enum SimpleEnum: ExampleProtocol {
    case Base

    var simpleDescription: String {
        get {
            return "A Simple Enum"
        }
        set {
            newValue
        }
    }

    mutating func adjust() {
        self.simpleDescription += ",adjusted"
    }
}

var c = SimpleEnum.Base
c.adjust()
let cDescription = c.simpleDescription

我还没有想出如何获得simpleDescription改变调用adjust()的结果。我的例子显然不会这样做，因为getter有一个硬编码的值，但是如何为simpleDescription设置一个值，同时仍然符合ExampleProtocol？

这是我的尝试：

protocol ExampleProtocol {
    var simpleDescription: String { get }
    mutating func adjust()
}

enum ExampleEnum : ExampleProtocol {
    case Base,Adjusted

    var simpleDescription: String {
        return self.getDescription()
    }

    func getDescription() -> String {
        switch self {
        case .Base:
            return "A simple description of enum"
        case .Adjusted:
            return "Adjusted description of enum"
        }
    }

    mutating func adjust() {
        self = ExampleEnum.Adjusted
    }
}

var c = ExampleEnum.Base
c.adjust()
let cDescription = c.simpleDescription