How to implement `Optional.zip` using variadic generics?

[Slava_Pestov]

@anon9791410

Have you come up with an example working required arguments into the mix? I'm not going to bother trying for now, given what you've demonstrated as the current state of the feature.

A required argument is easy, you just define a non-pack type parameter:

func foo<T, each U>(_: T, _: repeat each U)

@anon9791410

(Also, I didn't find this thread because I didn't think what we're doing is zipping. Is it zipping? I thought zipping was combining a number of elements together in tuples.)

Think of an optional as a sequence of zero or one elements.