n-ary assertions

notAWordAboutMacros.swift

protocol PayloadBearing_1 {
    typealias Payload_1 : Equatable
    func payload() -> Payload_1?
}

protocol PayloadBearing_2 : PayloadBearing_1 {
    typealias Payload_2 : Equatable
    func payload() -> (Payload_1, Payload_2)?
}

protocol PayloadBearing_3 : PayloadBearing_2 {
    typealias Payload_3 : Equatable
    func payload() -> (Payload_1, Payload_2, Payload_3)?
}


enum Foo : PayloadBearing_2 {
    case One(Int)
    case Two(Int, Int)

    func payload() -> Int? {
        if case let .One(value) = self {
            return value
        } else {
            return nil
        }
    }

    func payload() -> (Int, Int)? {
        if case let .Two(value) = self {
            return value
        } else {
            return nil
        }
    }
}

func assertSomething<T : PayloadBearing_2>(t: T, v: T.Payload_1?) -> Bool {
    return t.payload() == v
}

func assertSomething<T : PayloadBearing_2>(t: T, v: (T.Payload_1, T.Payload_2)?) -> Bool {
    switch (t.payload(), v) {
    case let (lhs?, rhs?) :
        return ((lhs.0 == rhs.0) &&
            (lhs.1 == rhs.1))
    case (.None, .None):
        return true
    case (.Some, .None), (.None, .Some):
        return false
    }
}

assertSomething(Foo.Two(3, 9), v: (3, 9))