Typed Method handles

[Rémi Forax]

On 06/09/2011 04:11 PM, Ali Ebrahimi wrote:
> Hi Remi,
>
>
> On Thu, Jun 9, 2011 at 4:49 PM, Rémi Forax<forax at univ-mlv.fr>  wrote:
>
>>   On 06/09/2011 12:33 PM, Ali Ebrahimi wrote:
>>
>> Hi Remi,
>> comments inlined.
>>
>> On Thu, Jun 9, 2011 at 1:49 PM, Rémi Forax<forax at univ-mlv.fr>  wrote:
>>
>>> On 06/09/2011 11:55 AM, Ali Ebrahimi wrote:
>>>> Hi all,
>>>> What happens if method handles takes variable arty of generic type
>>>> parameters.
>>>>
>>>> MethodHandle<void,int>   mh = #{x ->   System.out.println(x);};
>>>>
>>>> mh.invokeExack(1); //compiles
>>>>
>>>> mh.invokeExack("1"); //compile fail
>>>   I've proposed this syntax last year or before.
>>> There are 2 problems:
>>>   - it's a function type, so this means to introduce a new kind of type
>>> in the Java type system.
>>>   - it allows to use void and the primitives types between the angle
>>> bracket
>>>     which is not something allowed for the generics syntax.
>>>
>> This is not so hard. Method handles are new phenoms to platform and
>> compiler can handle them specially as polymorphic signature method
>> invocations handed.
>>
>> Best Regards,
>> Ali Ebrahimi
>>
>>   So this syntax was rejected for Java 8 but may be reconsidered later.
>>> Rémi
>>>
>> I think I know what a method handle is.
>> Polymorphic signature method like MH.invoke or MH.invokeGeneric are handled
>> by bypassing the method resolution used by the compiler.
>> That's why you have to specify the return type when calling such methods.
>> To summarize, the compiler does nothing and let the VM checks at runtime if
>> the invocation is safe or not.
>>
>> So you can't reuse this mechanism to implement function type.
>>
> I don't mean reuse the same mechanism, my intent is specially applying of
> generic type parameters for MethodHandle reference types and allowing them
> take arbitrary number of  type parameters in declaration.
> In this case, the compiler does not check number and types of them and
> accept them as is and use them for checking of methodhandle invocation
> expresions .
>
> MethodHandle<void,int>   mh1;
> MethodHandle<void,int,int>   mh2;
> MethodHandle  mh;
> ...
> mh1.invoke(1);
> mh2.invoke(1,2);
>
> for generic MethodHandle reference as mh1, mh2 compiler checks applicability
> of passed args in methodhandle invocation expresions and for non-generic
> once as mh don't do this check and works as current mechanism.
> mh.invoke(1,2,3,4);
>
> MethodHandle class itself does not any generic type parameters in
> definition.

But you just scratch the surface.
What about sybtyping between MethodHandle function type,
is a MethodHandle function type is a reified type,
is wildcard of MethodHandle function type allowed, is capture allowed,
is a MethodHandle function type can be inferred (what are the rules
for such inference), etc ?

> Best Regards
> Ali Ebrahimi

Rémi