On Wed, 2 Oct 2024 20:24:41 GMT, Chen Liang <li...@openjdk.org> wrote:
> First, some bit of history. These API methods are added before those > constants, and this patch did not change the type of these methods or > constants. Sure, makes sense to separate this patch from a potential type change of the methods/constants. > I believe the methods have restricted return types to be informative: `tag()` > is a U1, but it can be interpreted as a char (see [JVMS > 4.7.16.1](https://docs.oracle.com/javase/specs/jvms/se23/html/jvms-4.html#jvms-4.7.16.1)) > and thus is returned as one. CP tag is a U1 too (see [JVMS > 4.4](https://docs.oracle.com/javase/specs/jvms/se23/html/jvms-4.html#jvms-4.7.16.1)) > so maybe `byte` is just used out of convenience. I think `byte` and `char` as the types are a good choice given the way these tag items are described in the JVMS. > However, we usually use `int` to represent U1, also called unsigned bytes. > See > [`DataInput::readUnsignedByte`](https://github.com/openjdk/jdk/blob/c43202baf6eb7e49ec458037971a9efa392d053e/src/java.base/share/classes/java/io/DataInput.java#L323) > and > [`ClassReader::readU1`](https://github.com/openjdk/jdk/blob/c43202baf6eb7e49ec458037971a9efa392d053e/src/java.base/share/classes/java/lang/classfile/ClassReader.java#L133). > Guess that's why we used `int` for the constants. (Also, note that byte and > char are all [erased to > int](https://download.java.net/java/early_access/jdk24/docs/api/java.base/java/lang/classfile/TypeKind.html#computational-type) > in bytecode, so this has little practical effect and that might be why I > didn't bother to change these) One scenario where the unequal types of the methods and constants _does_ have a practical effect are JVM languages that don't have [binary numeric promotion](https://docs.oracle.com/javase/specs/jls/se23/html/jls-5.html#jls-5.6) for their [numerical equality operators](https://docs.oracle.com/javase/specs/jls/se23/html/jls-15.html#jls-15.21.1). This is the case for Kotlin's [value equality expressions](https://kotlinlang.org/spec/expressions.html#value-equality-expressions). This Kotlin code [would not compile](https://pl.kotl.in/A9D1WDdS8): fun isArray(a: AnnotationValue): Boolean { return a.tag() == AnnotationValue.TAG_ARRAY } Instead you would have to write [this code](https://pl.kotl.in/qSrwSIL39): fun isArray(a: AnnotationValue): Boolean { return a.tag() == AnnotationValue.TAG_ARRAY.toChar() } ------------- PR Review Comment: https://git.openjdk.org/jdk/pull/20773#discussion_r1790562651
