Difficult Trait Conformance

trait IterDataPipable:
    fn __next__[T: CollectionElement](ref[_] self) -> Optional[T]: pass

@value
struct ListDatapipe[T: CollectionElement](IterDataPipable[T]): 
    var src: List[T]
    var index: Int

    fn __init__(inout self, src: List[T]):
        self.src = src
        self.index = 0

    fn __init__(inout self, src: List[T], index: Int):
        self.src = src
        self.index = index

    fn __iter__(self) -> Self: return self

    fn __next__(ref[_] self) -> Optional[T]:
        self.index += 1
        if self.index == len(self.src) + 1:
            return Optional[T](None)

        return Optional[T](self.src[self.index - 1])

    fn __len__(self) -> Int: return len(self.src) - self.index

    var numbers = List(1,2,3,4,5)
    var pipe = ListDatapipe(numbers)
    # var pipe2 = AnotherPipe(pipe)
    # additional pipes
    var n = pipe.__next__()