On Fri, 6 May 2022 14:09:24 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. > > Jan Lahoda has updated the pull request incrementally with one additional > commit since the last revision: > > Reflecting review feedback. Looks good src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Flow.java line 752: > 750: Iterable<? extends > JCCaseLabel> labels) { > 751: Set<Symbol> coveredSymbols = new HashSet<>(); > 752: Map<Symbol, List<JCRecordPattern>> > deconstructionPatternsBySymbol = new HashMap<>(); since you seem to have settled on "recordPattern" for implementation names - you can probably revisit some of these names to say "record" instead of "deconstruction". src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Flow.java line 801: > 799: //i.e. represent all possible combinations. > 800: //This is done by categorizing the patterns based on the > type covered by the given > 801: //starting component. Example needed here. For instance (I discussed this with @biboudis): record Outer(R r) { }; sealed interface I { }; class A implements I { }; class B implements I { }; sealed interface R { }; record Foo(I i) implements R { } record Bar(I i) implements R { } switch (o) { case Outer(Foo(A), Foo(A)): case Outer(Foo(B), Foo(B)): case Outer(Foo(A), Foo(B)): case Outer(Foo(B), Foo(A)): case Outer(Bar(A), Bar(A)): case Outer(Bar(B), Bar(B)): case Outer(Bar(A), Bar(B)): case Outer(Bar(B), Bar(A)): } Which generates two sets: case Outer(Foo(A), Foo(A)): case Outer(Foo(B), Foo(B)): case Outer(Foo(A), Foo(B)): case Outer(Foo(B), Foo(A)): And case Outer(Bar(A), Bar(A)): case Outer(Bar(B), Bar(B)): case Outer(Bar(A), Bar(B)): case Outer(Bar(B), Bar(A)): Sorry for being pedantic - this code is tricky and I'm worried we'll all forget exactly how it works in 2 months :-) src/jdk.compiler/share/classes/com/sun/tools/javac/parser/JavacParser.java line 1014: > 1012: pattern = parsePattern(patternPos, mods, type, > false); > 1013: } else if (token.kind == LPAREN) { > 1014: pattern = parsePattern(patternPos, mods, type, > false); Nice! ------------- Marked as reviewed by mcimadamore (Reviewer). PR: https://git.openjdk.java.net/jdk/pull/8516
