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  1. JDK
  2. JDK-8269386

Imprecise type inference in the presence of ternary operator and wildcard

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    Details

    • Type: Bug
    • Status: Closed
    • Priority: P4
    • Resolution: Not an Issue
    • Affects Version/s: 11, 17, 18
    • Fix Version/s: None
    • Component/s: tools
    • Subcomponent:
    • CPU:
      generic
    • OS:
      generic

      Description

      A DESCRIPTION OF THE PROBLEM :
      In this program, javac infers a Captured type of `? extends Object` as the type of the variable `x`.
      I would expect to infer `B<? super T>`, since `B<? super T>` is more specific than `? extends Object`, and is a supertype of both `B<T>` and `B<? super T>`.


      STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
      javac A.java

      EXPECTED VERSUS ACTUAL BEHAVIOR :
      EXPECTED -
      Compile
      ACTUAL -
      A.java:5: error: incompatible types: B<CAP#1> cannot be converted to B<? super T>
          return x;
                 ^
        where T is a type-variable:
          T extends Object declared in class A
        where CAP#1 is a fresh type-variable:
          CAP#1 extends Object from capture of ? extends Object
      1 error

      ---------- BEGIN SOURCE ----------
      class A<T> {
        public A() {}
        public B<? super T> foo() {
          var x = (true) ? new B<T>() : (B<? super T>) null;
          return x;
          //return (true) ? new B<T>() : (B<? super T>) null; // This works
        }
      }

      class B<T> {
        public B() {}
      }
      ---------- END SOURCE ----------

      FREQUENCY : always


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              Assignee:
              Unassigned Unassigned
              Reporter:
              webbuggrp Webbug Group
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                Updated:
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