[External] : Re: New candidate JEP: 456: Unnamed Variables and Patterns

Wed Sep 27 13:33:26 UTC 2023

Hello Clement!

Thanks for letting us know. I recreated a stand alone reproduction of your report and indeed I get the verification error: https://bugs.openjdk.org/browse/JDK-8317048
Looking into it.

Angelos

________________________________
From: Clément BOUDEREAU <cboudereau at gmail.com>
Sent: 27 September 2023 09:55
To: Gavin Bierman <gavin.bierman at oracle.com>
Cc: Brian Goetz <brian.goetz at oracle.com>; Tagir Valeev <amaembo at gmail.com>; amber-dev at openjdk.org <amber-dev at openjdk.org>; Angelos Bimpoudis <angelos.bimpoudis at oracle.com>; amber-spec-experts <amber-spec-experts at openjdk.org>
Subject: [External] : Re: New candidate JEP: 456: Unnamed Variables and Patterns

Hi Amber dev team,

Firstly, thank you for the awesome work done.

I tried to use unnamed variable to simplifiy pattern matching in existing code with preview feature enable and JDK21 but ended up with runtime exception. The code compiles but unit test fails while I am actually running unit test with other preview feature.

Here is the PR with the problem and temporary workaround :
https://github.com/cboudereau/dataseries/pull/34<https://urldefense.com/v3/__https://github.com/cboudereau/dataseries/pull/34__;!!ACWV5N9M2RV99hQ!IQaUoSdPFw6-k9Xl8bh66a2ULWyr2pCGqHgDBldDFjJNesjswhMSNWPshaJor8k95x4FVDPHBA2WQlMKyak3HQUSGQ$>

FYI, I have another pull request to integrate as soon as possible preview feature of the latest jdk21 here where everything work fine locally :
https://github.com/cboudereau/dataseries/pull/24<https://urldefense.com/v3/__https://github.com/cboudereau/dataseries/pull/24__;!!ACWV5N9M2RV99hQ!IQaUoSdPFw6-k9Xl8bh66a2ULWyr2pCGqHgDBldDFjJNesjswhMSNWPshaJor8k95x4FVDPHBA2WQlMKyakzNtsm5g$>

Here is the error at runtime:

[ERROR]   SimpleTest.simple:17 ┬╗ Verify Bad local variable type
Exception Details:
  Location:
    io/github/cboudereau/dataseries/Union$Value.compareTo(Lio/github/cboudereau/dataseries/Union$Value;)I @297: aload
  Reason:
    Type top (current frame, locals[9]) is not assignable to reference type
  Current Frame:
    bci: @297
    flags: { }
    locals: { 'io/github/cboudereau/dataseries/Union$Value', 'io/github/cboudereau/dataseries/Union$Value', '[Z', 'io/github/cboudereau/dataseries/Union$Value$Tuple', integer, 'io/github/cboudereau/dataseries/Union$Value$Tuple', top, top, top, top, top, 'io/github/cboudereau/dataseries/Union$Value$Fixed', 'io/github/cboudereau/dataseries/Union$Value', integer, 'io/github/cboudereau/dataseries/Union$Value', integer }
    stack: { }
  Bytecode:
    0000000: 1278 c000 7a4d bb00 0c59 2a2b b700 0e59
    0000010: b800 1157 4e03 3604 2c05 0454 2d15 04ba
    0000020: 0017 0000 ab00 0000 0000 0014 0000 0001
    0000030: 0000 0000 0000 0022 bb00 1b59 0101 b700
    0000040: 1d2c 0604 54bf 2d3a 0519 052c 0704 54b6
    0000050: 0020 c000 243a 0c2c 0804 5403 360d 2c10
    0000060: 0604 5419 0c15 0dba 0026 0000 aa00 0000
    0000070: 0000 00df ffff ffff 0000 0001 0000 00df
    0000080: 0000 001c 0000 006d 1905 2c10 0704 54b6
    0000090: 0027 c000 243a 0e03 360f 190e 150f ba00
    00000a0: 2600 00aa 0000 002b ffff ffff 0000 0001
    00000b0: 0000 002b 0000 0019 0000 0022 032c 1008
    00000c0: 0454 a700 9404 2c10 0904 54a7 008b 0436
    00000d0: 0d2c 100a 0454 a7ff 8d19 052c 100b 0454
    00000e0: b600 27c0 0024 3a0e 2c10 0c04 5403 360f
    00000f0: 190e 150f ba00 2600 00aa 0000 0000 0047
    0000100: ffff ffff 0000 0001 0000 0047 0000 001b
    0000110: 0000 0024 022c 100d 0454 a700 3c19 0ec0
    0000120: 0001 3a0b 2c10 0e04 5419 09b4 002a 190b
    0000130: b400 2ab9 002e 0200 2c10 0f04 54a7 0019
    0000140: 0536 0d2c 1010 0454 a7ff 1b04 3604 2c10
    0000150: 1104 54a7 fec9 2c10 1204 54ac 4ebb 001b
    0000160: 592d b600 362d b700 1d2c 1013 0454 bf
  Exception Handler Table:
    bci [75, 82] => handler: 348
    bci [138, 146] => handler: 348
    bci [219, 227] => handler: 348
  Stackmap Table:
    append_frame(@28,Object[#122],Object[#12],Integer)
    same_frame(@56)
    same_frame(@70)
    full_frame(@99,{Object[#36],Object[#36],Object[#122],Object[#12],Integer,Object[#12],Top,Top,Top,Top,Top,Top,Object[#36],Integer},{})
    same_frame(@136)
    append_frame(@154,Object[#36],Integer)
    same_frame(@188)
    same_frame(@197)
    same_frame(@206)
    chop_frame(@217,2)
    append_frame(@240,Object[#36],Integer)
    same_frame(@276)
    same_frame(@285)
    same_frame(@320)
    chop_frame(@331,2)
    full_frame(@342,{Object[#36],Object[#36],Object[#122]},{Integer})
    same_locals_1_stack_item_frame(@348,Object[#52])

On Tue, Sep 26, 2023 at 6:14 PM Gavin Bierman <gavin.bierman at oracle.com<mailto:gavin.bierman at oracle.com>> wrote:
That’s right. We made a decision to simplify the grammar of switch labels for the JEP to only have a single pattern. However, if you use the "colon form” you can express similar code:

gmb at gmb-mac src % cat Switch.java
public class Switch {

    sealed interface X { }

    enum E implements X {A;}

    record R() implements X { }

    public void work(X x) {
        var result = switch (x) {
            case E.A:
            case R(): yield 42;
                // exhaustive!
        };
    }

    public static void main(String[] args) {
        System.out.println("complete");
    }
}
gmb at gmb-mac src % java Switch.java
complete

As you point out, a more uniform treatment would treat all constants as patterns and allow them all to appear in pattern lists of record patterns, for example. Working on it!!

Gavin

On 26 Sep 2023, at 14:52, Brian Goetz <brian.goetz at oracle.com<mailto:brian.goetz at oracle.com>> wrote:

I see now I answered a slightly different question :)

We do support case labels for enums in pattern switches, and they participate in exhaustiveness.  But we don't currently support mixing `case pattern, constant-label` in a single case label.  This is waiting for a more comprehensive treatment of constants as patterns.

On 9/26/2023 8:32 AM, Tagir Valeev wrote:

Hello! As we are finalizing this feature, can we squeeze in a little
improvement? Namely, support enum and patterns within the same case
label, provided that the patterns do not declare any variables. Like:

enum X {A, B}

static void test(Object obj) {
  switch (obj) {
    case String _, X.B -> System.out.println("B or String");
    default -> System.out.println("other");
  }
}

public static void main(String[] args) {
  Test.test("ddd");
  Test.test(X.B);
}

Currently, such a code is not supported. Or will it be considered in
future JEPs?

With best regards,
Tagir Valeev.

On Mon, Sep 25, 2023 at 6:25 PM Mark Reinhold <mark.reinhold at oracle.com><mailto:mark.reinhold at oracle.com> wrote:

https://openjdk.org/jeps/456

  Summary: Enhance the Java language with unnamed variables, which
  can be initialized but not used, and unnamed patterns, which match a
  record component without stating the component's name or type. Both are
  denoted by an underscore character, _.

- Mark

--
C.BOUDEREAU
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