CombinedComparable.swift

enum ComparisonOrdering: Int {
    case Ascending = 1
    case Descending = -1
    case Same = 0
}

infix operator <=> { precedence 130 }
protocol CombinedComparable: Comparable, Equatable {
    func <=>(lhs: Self, rhs: Self) -> ComparisonOrdering
}

func <<T: CombinedComparable>(lhs: T, rhs: T) -> Bool {
    return (lhs <=> rhs) == .Ascending
}

func ==<T: CombinedComparable>(lhs: T, rhs: T) -> Bool {
    return (lhs <=> rhs) == .Same
}


///////////


struct X: CombinedComparable {
    let value: Int
}

func <=>(lhs: X, rhs: X) -> ComparisonOrdering {
    if lhs.value < rhs.value {
        return .Ascending
    } else if lhs.value > rhs.value {
        return .Descending
    } else {
        return .Same
    }
}


let a = X(value: 0)
let b = X(value: 1)

a == b