On Tue, 4 May 2021 16:41:44 GMT, Jan Lahoda <jlah...@openjdk.org> wrote:
> This is a preview of a patch implementing JEP 406: Pattern Matching for > switch (Preview): > https://bugs.openjdk.java.net/browse/JDK-8213076 > > The current draft of the specification is here: > http://cr.openjdk.java.net/~gbierman/jep406/jep406-20210430/specs/patterns-switch-jls.html > > A summary of notable parts of the patch: > -to support cases expressions and patterns in cases, there is a new common > superinterface for expressions and patterns, `CaseLabelTree`, which > expressions and patterns implement, and a list of case labels is returned > from `CaseTree.getLabels()`. > -to support `case default`, there is an implementation of `CaseLabelTree` > that represents it (`DefaultCaseLabelTree`). It is used also to represent the > conventional `default` internally and in the newly added methods. > -in the parser, parenthesized patterns and expressions need to be > disambiguated when parsing case labels. > -Lower has been enhanced to handle `case null` for ordinary (boxed-primitive, > String, enum) switches. This is a bit tricky for boxed primitives, as there > is no value that is not part of the input domain so that could be used to > represent `case null`. Requires a bit shuffling with values. > -TransPatterns has been enhanced to handle the pattern matching switch. It > produces code that delegates to a new bootstrap method, that will classify > the input value to the switch and return the case number, to which the switch > then jumps. To support guards, the switches (and the bootstrap method) are > restartable. The bootstrap method as such is written very simply so far, but > could be much more optimized later. > -nullable type patterns are `case String s, null`/`case null, String s`/`case > null: case String s:`/`case String s: case null:`, handling of these required > a few tricks in `Attr`, `Flow` and `TransPatterns`. > > The specdiff for the change is here (to be updated): > http://cr.openjdk.java.net/~jlahoda/8265981/specdiff.preview.01/overview-summary.html src/java.base/share/classes/java/lang/runtime/SwitchBootstraps.java line 77: > 75: } > 76: > 77: private static<T extends CallSite> MethodHandle typeInitHook(T > receiver) { There is no point to have a type parameter here, private static MethodHandle typeInitHook(CallSite receiver) { will work the same src/java.base/share/classes/java/lang/runtime/SwitchBootstraps.java line 131: > 129: > 130: private static void verifyLabel(Object label) { > 131: if (Objects.isNull(label)) { `if (label == true) {` is more readable as said in the javadoc of `Objects.isNull` ------------- PR: https://git.openjdk.java.net/jdk/pull/3863
