[JDK-5052943] 4.10.4: Improve lub for lower-bounded wildcards and variables - Java Bug System

Type: Enhancement
Resolution: Unresolved
Priority: P4
Fix Version/s: tbd
Affects Version/s: 5.0, 7, 8
Component/s: specification
Labels:
- bound
- conditional
- expression
- inference
- jls-types
- lower
- noreg-doc
- super
- wildcards

Subcomponent:
language
Understanding:
Fix Understood
CPU:

generic
OS:

generic

In:

  static <T> T choose(boolean b, T trueValue, T falseValue) {
    return b ? trueValue : falseValue;
  }
  boolean b = false;
  List<? super Number> s = null;
  s = b ? s : s;
  s = choose(b, s, s);

Inference can't handle lower/super bounded wildcards leading to errors like:

Choose.java:10: incompatible types
found : java.util.List<capture of ? extends java.lang.Object>
required: java.util.List<? super java.lang.Number>
        s = b ? s : s;
              ^
Choose.java:11: incompatible types
found : java.util.List<capture of ? extends java.lang.Object>
required: java.util.List<? super java.lang.Number>
        s = choose(b, s, s);
                  ^

See the attached file Choose.java

###@###.### 2004-05-25

duplicates

JDK-6573446 javac infers a type bound where none should exist

Closed

relates to

JDK-8059898 4.10.4: lub incorrect for '? extends T', '? super T' combination

Closed

JDK-8068542 18.4: Improve resolution where lub is incompatible with an upper bound

Open

JDK-6480391 Unbounded wildcard '?' means '? extends Object'

Closed

JDK-8073129 The result of lub(C<U>, C<? super V>) is incorrect

Open

JDK-8061427 Type variables should have lower/super bounds

Closed

(1 relates to)

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Type: Enhancement
Resolution: Unresolved
Priority: P4
Fix Version/s: tbd
Affects Version/s: 5.0, 7, 8
Component/s: specification
Labels:
- bound
- conditional
- expression
- inference
- jls-types
- lower
- noreg-doc
- super
- wildcards

Subcomponent:
language
Understanding:
Fix Understood
CPU:

generic
OS:

generic

In:

  static <T> T choose(boolean b, T trueValue, T falseValue) {
    return b ? trueValue : falseValue;
  }
  boolean b = false;
  List<? super Number> s = null;
  s = b ? s : s;
  s = choose(b, s, s);

Inference can't handle lower/super bounded wildcards leading to errors like:

Choose.java:10: incompatible types
found : java.util.List<capture of ? extends java.lang.Object>
required: java.util.List<? super java.lang.Number>
        s = b ? s : s;
              ^
Choose.java:11: incompatible types
found : java.util.List<capture of ? extends java.lang.Object>
required: java.util.List<? super java.lang.Number>
        s = choose(b, s, s);
                  ^

See the attached file Choose.java

###@###.### 2004-05-25

duplicates

JDK-6573446 javac infers a type bound where none should exist

Closed

relates to

JDK-8059898 4.10.4: lub incorrect for '? extends T', '? super T' combination

Closed

JDK-8068542 18.4: Improve resolution where lub is incompatible with an upper bound

Open

JDK-6480391 Unbounded wildcard '?' means '? extends Object'

Closed

JDK-8073129 The result of lub(C<U>, C<? super V>) is incorrect

Open

JDK-8061427 Type variables should have lower/super bounds

Closed

(1 relates to)

Assignee:: Dan Smith

Reporter:: Peter Ahe

Votes:: 0 Vote for this issue

Watchers:: 2 Start watching this issue

Created:: 2004-05-25 17:25

Updated:: 2024-04-12 08:11

Imported:: 16/Sep/12 7:22 PM

Indexed:: 18/Jul/12 1:56 PM

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