On Tue, 3 May 2022 12:07:50 GMT, Jan Lahoda <jlah...@openjdk.org> wrote:
> 8262889: Compiler implementation for Record Patterns > > A first version of a patch that introduces record patterns into javac as a > preview feature. For the specification, please see: > http://cr.openjdk.java.net/~gbierman/jep427+405/jep427+405-20220426/specs/patterns-switch-record-patterns-jls.html > > There are two notable tricky parts: > -in the parser, it was necessary to improve the `analyzePattern` method to > handle nested/record patterns, while still keeping error recovery reasonable > -in the `TransPatterns`, the desugaring of the record patterns is very > straightforward - effectivelly the record patterns are desugared into > guards/conditions. This will likely be improved in some future version/preview > > `MatchException` has been extended to cover additional cases related to > record patterns. src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Flow.java line 783: > 781: } > 782: for (Entry<Symbol, List<JCDeconstructionPattern>> e : > categorizedDeconstructionPatterns.entrySet()) { > 783: if (coversDeconstructionStartingFromComponent(pos, > targetType, e.getValue(), 0)) { Here, the result of `e.getValue` is a reversed list of the observed patterns. For the switch below, switch (r) { case R(A a, A b) -> 1; case R(A a, B b) -> 2; case R(B a, A b) -> 3; case R(B a, B b) -> 4; } The 0th element of that list is the `R(B a, B b)` pattern, the 1st the `R(B a, A b)`. I am 99% sure that this is not a problem but I am pointing it out regardless, in case there is any underlying danger to that. ------------- PR: https://git.openjdk.java.net/jdk/pull/8516
