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  1. JDK
  2. JDK-8244513

[lworld] Typing of conditional expressions involving values.

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    Details

    • Type: Bug
    • Status: Resolved
    • Priority: P4
    • Resolution: Fixed
    • Affects Version/s: repo-valhalla
    • Fix Version/s: repo-valhalla
    • Component/s: tools
    • Labels:
    • Subcomponent:
    • CPU:
      generic
    • OS:
      generic

      Description

      Here are some notes from a discussion with Maurizio that need follow up:

      Looking at the rules for 'reference conditionals' javac should apply
      widening conversion in the following program's conditional expression and thereby type it to be X.I

      public class X {
          interface I {}
          static class Node implements I {
          }
          static void foo(Node e) {
              var ret = (e == null) ? new XNodeWrapper() : e;
          }
          static inline class XNodeWrapper implements I {
              int i = 42;
          }
          public static void main(String [] args) {
          }
      }

      (... "Otherwise, the second and third operands are of types S1 and S2 respectively. Let T1 be the type that results from applying boxing conversion to S1, and let T2 be the type that results from applying boxing conversion to S2. The type of the conditional expression is the result of applying capture conversion (§5.1.10) to lub(T1, T2).")

      But, more specifically, conditionals are divided in 3 categories:

      1) numeric conditionals -> all operands are numerics (either boxed or unboxed)
      2) boolean conditionals (boolean or Boolean operands)
      3) reference conditonals

      now, for (3) we go the widening way (e.g. we apply boxing)
      but for (1) we say If one of the second and third operands is of primitive type T, and the type of the other is the result of applying boxing conversion (§5.1.7) to T, then the type of the conditional expression is T and there's also this: If the second and third operands have the same type, then that is the type of the conditional expression. So ideally here we need a section on value conditional expressions and the rules perhaps should be similar to those for numerics which try to return an unboxed value as much as possible

      in other words, this is about whether we want inline classes to be more like Integer or like any reference class since our plan is to retrofit Integer to be an inline class perhaps this is a forced move and we have to stick with the numeric rules

      So, 4 cases:
      T.ref, T.ref -> type is T.ref
      T.val, T.val -> type is T.val
      T.ref, T.val -> type is T.val
      T.val, T.ref -> type is T.val

      now, in the NodeWrapper example, this is just a plain reference conditional, so javac should just apply widening

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              Assignee:
              sadayapalam Srikanth Adayapalam
              Reporter:
              sadayapalam Srikanth Adayapalam
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                Updated:
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