swift234

Introduce ExistentialMemberRefExpr for references to the members of
values of existential type, e.g.,

  var x : Printable
  x.print()

Existential member references reify the type of the implicit object
argument (implicitly, because we have no way of expressing this in the
type system), and replace the types of any other archetypes
with existential types that (don't, but will eventually) conform to
the protocols to which the archetypes conform.



Swift SVN r1963