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  1. JDK
  2. JDK-6790039

overhaul cast-conversion (umbrella)

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    Description

      Cast-conversion impl has several problems when it comes to generic types; most of them have to do with the fact that javac tries to be smarter than the JLS, in order to detect an illegal generic cast at compile-time rather than at runtime. Though this is desirable, the underlying impl is not reliable, meaning that a lot of valid cast are rejected by the compiler because of some failures in the 'provable distinct' test. Note also, that javac implements a stricter version of such a test than the JLS does - this is because we want to be able to detect more illegal cast than the JLS does.

      Here's an example:

      List<? extends Number> ln = ...
      Object o = (List<String>)ln; //error: inconvertible types

      The JLS require an unchecked warning here - because ? extends Number and String are not provably distinct; on the other hand, javac exploits the type info regarding the wildcard upper bound in order to reject that cast as illegal.

      Problem arise when either the target or the source type is

      *) a type variable with a recursive bound (fbound) - T extends Comparable<T>
      *) a captured type variable whose upper bound is recursive

      In such a setting, the enhanced type-disjointness test fails, that is, it is possible for javac to consider that two such types are distinct when they are not - the result is an unwanted complilation error where the user would have expected an unchecked warning.

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          relates to

          Bug - A problem which impairs or prevents the functions of the product. JDK-6541884 javac bug (JDK6): missing unchecked warning

          • P3 - Major loss of function.
          • Closed

          Bug - A problem which impairs or prevents the functions of the product. JDK-6557182 Unchecked warning *and* inconvertible types

          • P3 - Major loss of function.
          • Closed

          Bug - A problem which impairs or prevents the functions of the product. JDK-6569057 Generics regression on cast

          • P3 - Major loss of function.
          • Closed

          Bug - A problem which impairs or prevents the functions of the product. JDK-6467183 javac fails to raise unchecked warning on cast of parameterized generic subclass

          • P4 - Minor loss of function, or other problem where easy workaround is present.
          • Closed

          Bug - A problem which impairs or prevents the functions of the product. JDK-6526449 javac does not accept semantically valid == test

          • P4 - Minor loss of function, or other problem where easy workaround is present.
          • Closed

          Bug - A problem which impairs or prevents the functions of the product. JDK-6557279 Tweak provable distinctness

          • P4 - Minor loss of function, or other problem where easy workaround is present.
          • Closed

          Bug - A problem which impairs or prevents the functions of the product. JDK-6665356 Cast not allowed when both qualifying type and inner class are parameterized

          • P4 - Minor loss of function, or other problem where easy workaround is present.
          • Closed

          Bug - A problem which impairs or prevents the functions of the product. JDK-6270087 Javac rejects legal cast

          • P5 - Cosmetic problem like misspelt words or misaligned text.
          • Closed

          Bug - A problem which impairs or prevents the functions of the product. JDK-6507317 Problem when casting from parametrized type to concrete class

          • P5 - Cosmetic problem like misspelt words or misaligned text.
          • Closed

          Bug - A problem which impairs or prevents the functions of the product. JDK-6558558 Missing "unchecked" diagnostic

          • P5 - Cosmetic problem like misspelt words or misaligned text.
          • Closed

          Bug - A problem which impairs or prevents the functions of the product. JDK-6558559 Extra "unchecked" diagnostic

          • P5 - Cosmetic problem like misspelt words or misaligned text.
          • Closed

          Bug - A problem which impairs or prevents the functions of the product. JDK-6558569 Missing unchecked warning

          • P5 - Cosmetic problem like misspelt words or misaligned text.
          • Closed

          Bug - A problem which impairs or prevents the functions of the product. JDK-6559175 Unchecked cast, List<?> vs List<? extends Object>

          • P5 - Cosmetic problem like misspelt words or misaligned text.
          • Closed

          Bug - A problem which impairs or prevents the functions of the product. JDK-6559179 Unchecked upcast not identified

          • P5 - Cosmetic problem like misspelt words or misaligned text.
          • Closed

          Enhancement - null JDK-7005140 Cast: write new regression test checking all combinations

          • P4 - Minor loss of function, or other problem where easy workaround is present.
          • Open

          Enhancement - null JDK-6714835 Safe cast is rejected (with warning) by javac

          • P4 - Minor loss of function, or other problem where easy workaround is present.
          • Closed

          Bug - A problem which impairs or prevents the functions of the product. JDK-6932571 Compiling Generics causing Inconvertible types

          • P3 - Major loss of function.
          • Closed

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              mcimadamore Maurizio Cimadamore
              mcimadamore Maurizio Cimadamore
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