Aladdin - Scala Bugtracking
[#415] project: specification priority: low category: missing feature
submitter assigned to status date submitted
Vincent Martin won't fix 2005-04-08 18:08:55.0
subject Selections on non-path expressions create malformed types
code 
abstract class A {
  type T <: String;
  def x: T;
}

abstract class B {
  def a: A;
  val y: String  = a.x;
}
what happened 
slots.scala:8: malformed type: A#T
  val y: String  = a.x;
                    ^
one error found
what expected Silent compilation. I really think the compiler should automatically add temporary stable variables (val) to hold the value of expressions used as receiver objects. In the code above, the compiler should interpret the class B as: 
abstract class B {
  def a: A;
  val tmp = a;
  val y: String  = tmp.x;
}
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Changes of this bug report
Martin  edited on  2006-03-30 17:57:16.0
The problem with the proposed fix is that it is non-local. We could make the temporary variable local, as in val y: String = { val a$ = a; a$.x } but that would produce also an error.
Martin  edited on  2006-10-07 13:24:40.0
I have put in a fix that approximates the type from above instead of throwing a malformed exception. This needs to be speced still.
Martin  edited on  2006-10-31 13:36:10.0
Martin  edited on  2006-12-01 17:30:28.0
I got convinced b recent bug reports that hiding this sort of bug is a bad thing. Very often it leads to obscure behavior later on. So I revert the changes to the compiler that approximate types, and leave the spec as it is.