SAM identity or at least equals/hashCode

[Ali Ebrahimi]

Hi,
yes, of course, i'm working on.

Ali Ebrahimi

On Tue, Jun 21, 2011 at 6:29 PM, Brian Goetz <brian.goetz at oracle.com> wrote:

> Care to share your translation strategy?
>
>
> On 6/21/2011 10:48 AM, Ali Ebrahimi wrote:
>
>> Hi, I know that.
>>
>> I think we can convert  all statefull lambdas to stateless ones in
>> desugering phase.
>>
>> Ali ebrahimi
>>
>> On Tue, Jun 21, 2011 at 5:57 PM, Brian Goetz <brian.goetz at oracle.com
>> <mailto:brian.goetz at oracle.com**>> wrote:
>>
>>    The compiler desugars the lambda to a method that has two
>>    parameters. SAM converting that method to one that has no parameters
>>    can be accomplished in a number of ways -- generating bytecode for
>>    the method that does the currying, MethodHandle.insertArguments, etc.
>>
>>
>>    On 6/21/2011 10:20 AM, Ali Ebrahimi wrote:
>>
>>        Hi,
>>        how do you handle it if you have more than one captured (bound)
>>        state?
>>
>>        public Adder adderGenerator(int x, int y) { return #{ ->  x + y} };
>>
>>        Ali Ebrahimi
>>        On Tue, Jun 21, 2011 at 5:36 PM, Peter
>>        Levart<peter.levart at marand.si
>>        <mailto:peter.levart at marand.si**>>__wrote:
>>
>>
>>            On 06/21/11, Brian Goetz wrote:
>>
>>                        If you want to refer to the object instance that
>>                        is the result of
>>                        SAM conversion, call that the SAM instance or
>>                        the SAM object --
>>                        which is an object.  (You can't assume much
>>                        about its identity --
>>                        the compiler will likely make sure that all
>>                        instances of
>>                        "stateless" lambdas are really the same object,
>>                        a la the
>>                        "Flyweight" pattern.)
>>
>>
>>                    Only stateless? Why?
>>
>>
>>                Lambdas can capture final local variables.  Consider:
>>
>>                public IntFactory constGenerator(int x) { return #{ ->
>>                  x } };
>>
>>
>>            This is exactly the use case I'm talking about. One would
>>            want that
>>
>>            constGenerator(12).equals(__**constGenerator(12)) would
>>            evaluate to true and
>>            constGenerator(12).equals(__**constGenerator(13)) would
>>            evaluate to false
>>
>>            event though the instances of two SAM objects returned from
>>            two invocations
>>            of method:
>>
>>            constGenerator(12)
>>
>>            are not the same instance, they could be equal.
>>
>>                Clients will call the resulting IntFactory with
>>                    foo.make()
>>                and expect an int to come back.  The SAM-converted
>>                lambda is an object,
>>                it has to have a nilary make() method, that method has
>>                captured state x,
>>                so where do we store the captured state?
>>
>>
>>            I belive you (could) generate a static method with one
>>            formal parameter:
>>
>>            private static int lambda$1(Integer p1) { return p1; }
>>
>>            ...then obtain a MethodHandle for it, say: lambda$1Mh
>>            ...then capture the final x: lambda$1BoundMh =
>>            lambda$1Mh.bindTo(x);
>>
>>            now the SAM-converted lambda object has a reference to
>>            lambda$1BoundMh. It
>>            uses it to delegate the invocation of it's nilary make()
>>            method to. So why
>>            could it not use it to delegate equals/hashCode methods too?
>> The
>>            prerequisite is of course that MethodHandle(s) define
>>            meaningfull
>>            equals/hashCode methods that take into account the captured
>>            (bound) state
>>            and any final target method identity too. That's what I had
>>            in mind.
>>
>>            For the above example, lambda$1BoundMh would implement
>>            equals/hashCode in
>>            terms of delegating to bound Object (Integer in our case)
>>            and to the wrapped
>>            MH lambda$1Mh. The final lambda$1Mh would implement
>>            equals/hashCode in terms
>>            of target lambda$1 method signature.
>>
>>            Now, I don't know much about MHs and how they are
>>            implemented and optimized
>>            in the VM, so perhaps such scheme would defeat those
>>            optimizations. Or is it
>>            still possible?
>>
>>            Regards, Peter
>>
>>
>>
>>
>>
>>
>>