Add/collection strawman

[odersky]

Two additiions:

1. A new strawman centered around views rather than iterators
2. An improvement to overloading resolution which lets us use the Scala 2.8 calling
   idioms for map on String. Previously, this required an explicit type annotation.

[DarkDimius]

AFAIK Rust initially had RandomAccessIterator, but then they decided to drop it. It was creating more problems than solving.

[lrytz]

Looked a bit more through the strawman

• Could Iterator and View be unified?
• What's the intended use for IterableOnce?

[DarkDimius]

Could Iterator and View be unified?

The only diffence between view and iterator lies in fact that views can be traversed several times.
In my variation of the original strawman, I was proposing to make this change:

class View[A](val v: ()=> Iterator[A]) extends AnyVal

Ie: view is just a producer of iterators

[lrytz]

Ah, thanks - so the by-name here is crucial:

object View {
  def fromIterator[A](it: => Iterator[A]): View[A] = new View[A] { def iterator = it }
}

[adriaanm]

Implementing this in 2.12.0-RC1 broke existing code: https://issues.scala-lang.org/browse/SI-9943. It had a pretty weird overload where one parameter list was implicit and the other wasn't. We could ad-hoc exclude those cases, as the programmer probably doesn't think of them as overloaded, but that seems pretty, well, ad-hoc.

[odersky]

Alternatively, demand that all parameter types are the same. That's what dotty does currently. It compiles the code in SI-9943 OK.

[adriaanm]

Yep, this is the main aspect where Scala 2's implementation differs. It seemed more regular to me to just lub the argument types, but maybe we need to be more strict, based on this bug report.

[adriaanm]

Interestingly, this turned out to be a different problem: we admitted sealed classes (like <:<) as SAM types. Closing that hole made the type checker happy.