Hi Uwe, you're welcome. Note it's up for review now: http://mail.openjdk.java.net/pipermail/core-libs-dev/2016-May/041211.html
Best, Michael > Am 13.05.2016 um 11:54 schrieb Uwe Schindler <uschind...@apache.org>: > > Hi, > > OK, thanks for creating an issue! > > Uwe > > ----- > Uwe Schindler > uschind...@apache.org > ASF Member, Apache Lucene PMC / Committer > Bremen, Germany > http://lucene.apache.org/ > >> -----Original Message----- >> From: Remi Forax [mailto:fo...@univ-mlv.fr] >> Sent: Friday, May 13, 2016 10:37 AM >> To: Uwe Schindler <uschind...@apache.org> >> Cc: Michael Haupt <michael.ha...@oracle.com>; Core-Libs-Dev <core-libs- >> d...@openjdk.java.net> >> Subject: Re: MethodHandle for array length >> >> Hi Uwe, >> I was planning to add a bug for this feature but it seems that Michael was >> faster than me, >> https://bugs.openjdk.java.net/browse/JDK-8156915 >> >> regards, >> Rémi >> >> ----- Mail original ----- >>> De: "Uwe Schindler" <uschind...@apache.org> >>> À: "Michael Haupt" <michael.ha...@oracle.com>, "Core-Libs-Dev" <core- >> libs-...@openjdk.java.net> >>> Envoyé: Jeudi 12 Mai 2016 14:34:34 >>> Objet: RE: MethodHandle for array length >>> >>> Hi Michael, >>> >>>>> Am 11.05.2016 um 21:35 schrieb Uwe Schindler >> <uschind...@apache.org>: >>>>> With Java 9 this gets a bit worse: There is no "easy way" with the >>>> MethodHanldes class to generate a MethodHandles.countedLoop() on all >>>> elements of an array: >>>>> >>>>> public static MethodHandle countedLoop(MethodHandle iterations, >>>> MethodHandle init, MethodHandle body) [new in Java 9] >>>> >>>> this isn't a remedy when you need the index in each iteration, but you >> can >>>> generate a loop over all elements of an array using iteratedLoop(), as >>>> illustrated by this test from LoopCombinatorTest: >>>> >>>> @Test >>>> public static void testIterateSum() throws Throwable { >>>> // Integer[] a = new Integer[]{1,2,3,4,5,6}; int sum = 0; for (int e : >>>> a) { sum >>>> += e; } return sum; => 21 >>>> MethodHandle loop = >>>> MethodHandles.iteratedLoop(Iterate.MH_sumIterator, >> Iterate.MH_sumInit, >>>> Iterate.MH_sumStep); >>>> assertEquals(Iterate.MT_sum, loop.type()); >>>> assertEquals(21, loop.invoke(new Integer[]{1, 2, 3, 4, 5, 6})); >>>> } >>>> >>>> ... where MH_sumIterator is a handle to this method: >>>> >>>> static Iterator<Integer> sumIterator(Integer[] a) { >>>> return Arrays.asList(a).iterator(); >>>> } >>> >>> Of course this works, too. >>> >>> My proposal or question here was more about the API inconsistency in >> general. >>> You can do a lot here and there, you can implement effective or >>> non-effective loops with MethodHandles, but still the following holds true: >>> java.lang.invoke.MethodHandles is missing an accessor for "array.length", >>> which is not understandable. The "countedLoop" here was just an example >> use >>> case (if that one is great or not does not matter), it was just posted to >>> actually show the API and how it *could* be used. >>> >>> The real example from our script engine was not related to loops, it was an >>> actual invokedynamic callsite implementation where it was not possible to >>> figure out how to get a method handle to the very special arraylength byte >>> code, aka "array.length javac sugar". Everything else to handle arrays is >>> there at one single place, but the array length is missing and you get very >>> annoyed. If you are not so familiar to bytecode and the mechanics behind, >>> you have a very hard time to find out how to do this: the intuitive >>> solutions does not work: "array.length" -> aha it’s a field, so let's try >>> Lookup.findGetter(long[].class, "length", int.class) -> does not work! >>> >>> What is so hard to accept the proposal to have >>> MethodHandles.arrayLengthGetter, implemented in the most effective >> way (as a >>> methodhandle that solely calls the special bytecode "arraylength")? In fact >>> thais is like a 10 liner to implement + Javadocs. No need to delay a >>> release, there are still changes in JDK 9 going on that are far more risky >>> than this. >>> >>> Best, >>> Uwe -- <http://www.oracle.com/> Dr. Michael Haupt | Principal Member of Technical Staff Phone: +49 331 200 7277 | Fax: +49 331 200 7561 Oracle Java Platform Group | LangTools Team | Nashorn Oracle Deutschland B.V. & Co. KG | Schiffbauergasse 14 | 14467 Potsdam, Germany ORACLE Deutschland B.V. & Co. KG | Hauptverwaltung: Riesstraße 25, D-80992 München Registergericht: Amtsgericht München, HRA 95603 Komplementärin: ORACLE Deutschland Verwaltung B.V. | Hertogswetering 163/167, 3543 AS Utrecht, Niederlande Handelsregister der Handelskammer Midden-Nederland, Nr. 30143697 Geschäftsführer: Alexander van der Ven, Jan Schultheiss, Val Maher <http://www.oracle.com/commitment> Oracle is committed to developing practices and products that help protect the environment
