Thanks, Chris. I've used this trick to implement "nop" in invokebinder:
MethodHandle ignoreException = Binder
.from(void.class, RuntimeException.class, String[].class)
.nop();
- Charlie
On Tue, Jan 24, 2012 at 2:53 AM, Noctarius <m...@noctarius.com> wrote:
> Hi Charlie
> The same "hack" applies to every situation where a generic
> returntype "needs" to defined but is not needed in the end. Void
> is the wrapper type to void and the returnvalue is just discarded
> whatever it was.
>
> Cheers
> Chris
>
> Am 24.01.2012 08:26, schrieb Charles Oliver Nutter:
>> Oh, that does seem to work...what an ugly hack. And actually,
>> you can just use Object.class but cast the resulting return to
>> void, and it works.
>>
>> So basically, I do this:
>>
>> handler = MethodHandles.constant(Object.class, null) handler =
>> MethodHandles.asType(void.class) handler =
>> MethodHandles.dropArguments(0, Throwable.class, String.class)
>>
>> And then use that as the exception handler.
>>
>> It's not exactly the no-op I wanted, since it has the cast
>> logic in there, but it's close enough.
>>
>> FWIW, I'm using this in the tests for invokebinder, for testing
>> the tryFinally operation:
>>
>> public void testTryFinally3() throws Throwable { MethodHandle
>> post = Binder .from(void.class, String[].class)
>> .invokeStatic(MethodHandles.lookup(), BinderTest.class,
>> "finallyLogic");
>>
>> MethodHandle ignoreException = Binder .from(void.class,
>> RuntimeException.class, String[].class) .drop(0, 2)
>> .cast(Object.class) .constant(null);
>>
>> MethodHandle handle = Binder .from(void.class, String[].class)
>> .tryFinally(post) .catchException(RuntimeException.class,
>> ignoreException) .invokeStatic(MethodHandles.lookup(),
>> BinderTest.class, "setZeroToFooAndRaise");
>>
>> assertEquals(MethodType.methodType(void.class, String[].class),
>> handle.type()); String[] stringAry = new String[1]; try {
>> handle.invokeExact(stringAry); } catch (RuntimeException re) {
>> assertTrue("should not have reached here", false); }
>> assertEquals("foofinally", stringAry[0]); }
>>
>> invokebinder is my MethodHandle DSL, so I don't have to stand
>> on my head while building MH chains :)
>>
>> https://github.com/headius/invokebinder
>>
>> - Charlie
>>
>> On Tue, Jan 24, 2012 at 1:07 AM, Noctarius <m...@noctarius.com>
>> wrote:
>>> Hi Charly,
>>>
>>> why not use Void and return null what behaves like using void
>>> as the return type.
>>>
>>> Cheers Chris
>>>
>>> Am 24.01.2012 08:01, schrieb Charles Oliver Nutter:
>>>> I discovered a possible gap in the MethodHandles API.
>>>>
>>>> Say I want to create an exception handler that does nothing
>>>> but ignore the exception. The target handle is a method
>>>> that looks like this:
>>>>
>>>> void foo(String)
>>>>
>>>> I have my "target" handle pointing at foo.
>>>>
>>>> I want to catch all Throwable and ignore them, so I would
>>>> build up a method handle chain that does the following
>>>> (top-down)
>>>>
>>>> 1. receives arguments (Throwable, String) and returns void
>>>> 2. drops both arguments 3. ???
>>>>
>>>> There's no endpoint I can attach it to for a "no-op" void
>>>> return.
>>>>
>>>> "constant" doesn't work because it returns a value, and
>>>> explicitly forbids void return type.
>>>>
>>>> "identity" doesn't work because it returns a value and
>>>> receives one argument.
>>>>
>>>> What I need here is something like MethodHandles.constant,
>>>> but that takes no arguments and has a void return.
>>>> MethodHandles.nop anyone?
>>>>
>>>> I could filterReturn, but I still would have to attach it
>>>> to an external method...there's no way to create a filter
>>>> that returns void entirely with method handles.
>>>>
>>>> Am I missing something?
>>>>
>>>> - Charlie _______________________________________________
>>>> mlvm-dev mailing list mlvm-dev@openjdk.java.net
>>>> http://mail.openjdk.java.net/mailman/listinfo/mlvm-dev
>>>
>>>
>>> --
>>>
>>>
>>> ############################## # A Digital's Life
>>> # ############################## Nickname: Noctarius
>>> Location: Germany
>>>
>>> Meet me at: Ohloh: http://www.ohloh.net/accounts/noctarius
>>> Web: http://www.noctarius.com XMPP/Jabber:
>>> noctar...@jabber.ccc.de
>>> _______________________________________________ mlvm-dev
>>> mailing list mlvm-dev@openjdk.java.net
>>> http://mail.openjdk.java.net/mailman/listinfo/mlvm-dev
>> _______________________________________________ mlvm-dev
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>
>
> --
>
>
> ##############################
> # A Digital's Life #
> ##############################
> Nickname: Noctarius
> Location: Germany
>
> Meet me at:
> Ohloh: http://www.ohloh.net/accounts/noctarius
> Web: http://www.noctarius.com
> XMPP/Jabber: noctar...@jabber.ccc.de
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