RFR: 8282274: Compiler implementation for Pattern Matching for switch (Third Preview) [v3]

[Vicente Romero]

On Tue, 12 Apr 2022 13:18:14 GMT, Jan Lahoda <jlahoda at openjdk.org> wrote:

>> This is a (preliminary) patch for javac implementation for the third preview of pattern matching for switch (type patterns in switches).
>> 
>> Draft JLS:
>> http://cr.openjdk.java.net/~gbierman/PatternSwitchPlusRecordPatterns/PatternSwitchPlusRecordPatterns-20220407/specs/patterns-switch-jls.html
>> 
>> The changes are:
>> -there are no guarded patterns anymore, guards are not bound to the CaseElement (JLS 15.28)
>> -a new contextual keyword `when` is used to add a guard, instead of `&&`
>> -`null` selector value is handled on switch level (if a switch has `case null`, it is used, otherwise a NPE is thrown), rather than on pattern matching level.
>> -total patterns are allowed in `instanceof`
>> -`java.lang.MatchException` is added for the case where a switch is exhaustive (due to sealed types) at compile-time, but not at runtime.
>> 
>> Feedback is welcome!
>> 
>> Thanks!
>
> Jan Lahoda has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Cleanup.

src/jdk.compiler/share/classes/com/sun/tools/javac/code/Source.java line 242:

> 240:         PATTERN_SWITCH(JDK17, Fragments.FeaturePatternSwitch, DiagKind.PLURAL),
> 241:         REDUNDANT_STRICTFP(JDK17),
> 242:         TOTAL_PATTERN_IN_INSTACEOF(JDK17, Fragments.FeatureTotalPatternsInInstanceof, DiagKind.PLURAL),

shouldn't be JDK19?

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PR: https://git.openjdk.java.net/jdk/pull/8182