Starting to implement Variadic Generics

[technicated (Andrea Tomarelli)]

@Joe_Groff

In my thinking, we kinda already closed off that "variadics are just tuples" avenue once we committed to breaking up function arguments. That means that there are now at least two expression contexts we'd want to be able to "unpack" into. Nonetheless, we can probably limit the number of places you need variadic declarations compared to C++, since we ought to make it easy to pack into and unpack from tuple values.

One benefit of tuples preserving their built-in status is that we can maintain the "unlabeled single-element tuple types are equivalent to their element type" invariant (in other words, (T) and T are always the same type), which is important for the ergonomics of variadic returns or fields, since you don't want to have to unwrap them in the single element case.

Regarding this, in reality I initially thought (like Chris) that the variadic generics could be sugar for tuples, as I expressed in my other thread; but this is obvious subject to discussion and your point on (T) and T is a good reminder of the implications one should consider when relating new features to tuples.

@Joe_Groff

As a forum etiquette thing, I wonder whether it'd be a good idea to start pitch threads on this and the other "tuple literals" thread, so that these development threads can remain focused on implementation questions.

I'm not sure if this is a reply to Chris's post or mine, but in any case I agree with you and would like to invite anyone interested to participate to my other thread for discussion / pitching so that this thread can "only" collect informations about implementation-level stuff