Generic enums

In the following example, we will build a fully generic light:

enum State<T>: Equatable where T: Equatable {
    case on
    case off
    case dimmed(T)
}

struct Bits8Dimming: Equatable {
    let value: Int
    init(_ value: Int) {
        assert(value > 0 && value < 256)
        self.value = value
    }
}

struct ZeroOneDimming: Equatable {
    let value: Double
    init(_ value: Double) {
        assert(value > 0 && value < 1)
        self.value = value
    }
}

let nostalgiaState: State<Bits8Dimming> = .dimmed(.init(10))
let otherState: State<ZeroOneDimming> = .dimmed(.init(0.4))

The dim type is now specified as a part of the State type. This gives us a lot of flexibility, as well as validation. Wrapping the value into a small struct adds very little overhead in terms of performance, and allows us to ensure that the values are sane before being set into our enum.