在子句中的Swift元组

class Generic<T> {
    var value: T

    init(value: T) {
        self.value = value
    }
}

protocol Tuple2 {
    typealias A
    typealias B
    var i0: A { get }
    var i1: B { get }
}

protocol Tuple3: Tuple2 {
    typealias C
    var i2: C { get }
}

struct Tuple2Impl<A,B>: Tuple2 {
    var i0: A
    var i1: B

    init(_ i0: A,_ i1: B) {
        self.i0 = i0
        self.i1 = i1
    }
}
struct Tuple3Impl<A,C>: Tuple3 {
    var i0: A
    var i1: B
    var i2: C

    init(_ i0: A,_ i1: B,_ i2: C) {
        self.i0 = i0
        self.i1 = i1
        self.i2 = i2
    }
}

extension Generic where T: Tuple2 {
    func append<C>(c: C) -> Generic<Tuple3Impl<T.A,T.b,C>> {
        return Generic<Tuple3Impl<T.A,C>>(value: Tuple3Impl(value.i0,value.i1,C))
    }
}

var a = Generic(value: Tuple2Impl("Hello",256))

print(a.append(3.14).value.i2)