SIP: Curried varargs

Scala Improvement Process
8

At alternate way of translating :_* could be to translate it to a method with a default implementation,
so it could be overridden if there’s a more efficient way of handling it known to the programer.

For example:

f(a, b, c:_*)

Would be translated into this:

f.applyBegin
  .applyNext(a)
  .applyNext(b)
  .applyNextSeq(c)
  .applyEnd

The default implementation of applyNextSeq could be something along these lines:

def applyNextSeq[A](as: Seq[A]): ListBuilder[A] = as.foldLeft(this)(_.applyNext(_))

But, if the programmer knows a better way of doing this, it could be overridden (using the ListBuilder example from above):

class ListBuilder[A] {
  def applyNext[B >: A](b: B): ListBuilder[B] = ???
  def applyNextSeq[B >: A](b: Seq[B]): ListBuilder[B] = ???
  def applyEnd: List[A] = ???
}
object List extends Curried {
  def applyBegin[A]: ListBuilder[A] = ???
}

I could be missing something, but this is basically a simple desugaring, and I think that changing pattern matching to be isomorphic would require deeper changes to the compiler.

1 Like