Problem with method references

[Tomasz Kowalczewski]

Thanks for the information.

Previously I used JDK build 120 and had some other problems. Will it
be of any benefit to the dev community if I share these? Or should I
wait till the prototype is in sync with java.dyn and retry?

-- 
Tomasz Kowalczewski


On Sun, Jan 2, 2011 at 10:29 PM, Rémi Forax <forax at univ-mlv.fr> wrote:
> Hi Tomasz,
> jdk7b123 comes with a new version of package java.dyn.
> so the source of the prototype compiler and the source of jdk7
> are not in sync.
>
> For the record, Methodhandle.invoke should be MethodHandle.invokeGeneric
> and SAM interface conversion should use MethodHandles.asInstance().
>
> Rémi
>
> On 01/02/2011 08:28 PM, Tomasz Kowalczewski wrote:
>> Hi All,
>>
>> I got latest code for lambda prototype and started to play with it a
>> little. I have encountered problems when using method references.
>>
>> I checked out the code using:
>>
>> hg clone http://hg.openjdk.java.net/lambda/lambda/langtools
>>
>> and compiled it against build 1.7.0-ea-fastdebug-b123.
>>
>> I have following problems when compiling/running my sample code:
>>
>> 1) This example does not compile.
>>
>> package org.tkowalcz.lambda.extractor;
>>
>> public class Lambda {
>>
>>    public static void main( String[] args ) {
>>      Extractor x = (Extractor) Lambda#getArgCount;
>>      x.extract( new Lambda() );
>>    }
>>
>>    public int getArgCount() {
>>      return 0;
>>    }
>> }
>>
>> interface Extractor {
>>
>>    int extract( Lambda lambda );
>> }
>>
>> Compiler output (from within ant):
>>
>>       [exec] src\org\tkowalcz\lambda\extractor\Lambda.java:6: cannot find symbol
>>       [exec]     Extractor x = Lambda#getArgCount;
>>       [exec]                   ^
>>       [exec]   symbol:   method<int>invoke(Lambda)
>>       [exec]   location: class MethodHandle
>>       [exec] Fatal Error: Unable to find method invoke
>>
>> 2) After adding a cast to Extractor it will compile but will throw
>> ClassCastException when run:
>>
>> public class Lambda {
>>
>>    public static void main( String[] args ) {
>>      Extractor x = (Extractor) Lambda#getArgCount;
>>      x.extract( new Lambda() );
>>    }
>>
>>    public int getArgCount() {
>>      return 0;
>>    }
>> }
>>
>> abstract class Extractor {
>>
>>    public abstract int extract( Lambda lambda );
>> }
>>
>>       [exec] Exception in thread "main" java.lang.ClassCastException:
>> sun.dyn.DirectMethodHandle cannot be cast to
>> org.tkowalcz.lambda.extractor.Extractor
>>       [exec]  at org.tkowalcz.lambda.extractor.Lambda.main(Lambda.java:6)
>>       [exec] VM option '+UnlockExperimentalVMOptions'
>>       [exec] VM option '+EnableInvokeDynamic'
>>
>> 3) However, when I change abstract class Extractor to interface then
>> removing the cast will let my code compile and run:
>>
>> public class Lambda {
>>
>>    public static void main( String[] args ) {
>>      Extractor x = Lambda#getArgCount;
>>      x.extract( new Lambda() );
>>    }
>>
>>    public int getArgCount() {
>>      return 0;
>>    }
>> }
>>
>> interface Extractor {
>>
>>    int extract( Lambda lambda );
>> }
>>
>> I hope that 1) and 2) is a correct usage and I am not abusing the
>> prototype too much.
>>
>
>
>