ParamForwarding: questions

[DarkDimius]

https://github.com/lampepfl/dotty/blob/master/src/dotty/tools/dotc/transform/ParamForwarding.scala#L22

/** For all parameter accessors
 *
 *      val x: T = ...
 *
 *  if
 *  (1) x is forwarded in the supercall to a parameter that's also named `x`
 *  (2) the superclass parameter accessor for `x` is accessible from the current class
 *  change the accessor to
 *
 *    def x: T = super.x.asInstanceOf[T]
 *
 *  Do the same also if there are intermediate inaccessible parameter accessor forwarders.
 *  The aim of this transformation is to avoid redundant parameter accessor fields.
 */

I have several questions to what this phase does:

1. Why do names matter?
2. if indeed name has not changed, is not it better to remove def entirely? Than virtual dispatch will do the same that def x: T = super.x.asInstanceOf[T] does. (I guess the answer is that types could be different, but I want to make sure that there are no other reasons)

[odersky]

Why do names matter?

To limit the search space, and make it more predictable.

if indeed name has not changed, is not it better to remove def entirely? Than virtual dispatch will do the same that def x: T = super.x.asInstanceOf[T] does. (I guess the answer is that types could be different, but I want to make sure that there are no other reasons)

And we also need a witness for the parameter accessor later on (that's something pickling/unpickling needs, for instance)

[DarkDimius]

And we also need a witness for the parameter accessor later on (that's something pickling/unpickling needs, for instance)

@odersky following examples from #776 scalac does not create such method. The examples in #776 also suggest that we cannot create def x, as either private or protected or public or default. We either need to remove the method(as scalac does) or to name mangle it.