Conformance at declaration

The first method to declare a conformance is to do it at the top level, when you declare your custom type. You'll notice that the raw representation comes first, then the protocol conformance:

enum State: Int, Toggling {
    case off = 0
    case on
    
    mutating func toggle() {
        self = self == .on ? .off : .on
    }
}

var state: State = .on
state.toggle()
assert(state == .off)