Hey Kristoffer,
sorry for the late reply. I was on vacation.
Here you can find my initial email that also contains a description and
a link to the patch:
http://mail.openjdk.java.net/pipermail/compiler-dev/2015-January/009220.html
The Eclipse JDT team didn't really need a patch. Their compiler does not
throw away generic type information in early stages so it was easy to
add them to the generic signature (which "accidentally" happened at the
beginning and now works again with help of a compiler option):
https://bugs.eclipse.org/bugs/show_bug.cgi?id=449063
The OpenJDK/Oracle JDK compiler mainly works without generic type
information (they call "erasure()" intentionally), so the produced class
files do not contain information that can be determined by any hacks.
It would be great if we could convince them. I think many projects need
more type-safety for lambda expressions.
On 18.08.2015 14:58, Stephan Ewen wrote:
Timo should still have the patch!
If you want to re-vive the thread, that'd be great. I'd be happy to
support it.
On Tue, Aug 18, 2015 at 2:51 PM, Kristoffer Sjögren <sto...@gmail.com
<mailto:sto...@gmail.com>> wrote:
Do you have a link to these patches?
Reading through the thread, I get the feeling they didn't reject the
idea completely.
Considering there are also other projects (Crunch, Spark, Storm, etc)
that would benefit from this, maybe we can convince them together?
On Tue, Aug 18, 2015 at 2:27 PM, Stephan Ewen <se...@apache.org
<mailto:se...@apache.org>> wrote:
> Yep, Timo wrote the patch, both for OpenJDK and JDT - the JDT
one was
> accepted in the end.
>
>
> On Tue, Aug 18, 2015 at 2:09 PM, Robert Metzger
<rmetz...@apache.org <mailto:rmetz...@apache.org>> wrote:
>>
>> Exactly, Timo opened the thread.
>>
>> On Tue, Aug 18, 2015 at 2:04 PM, Kristoffer Sjögren
<sto...@gmail.com <mailto:sto...@gmail.com>>
>> wrote:
>>>
>>> Yeah, I think I found the thread already... by Timo Walther?
>>>
>>> On Tue, Aug 18, 2015 at 2:01 PM, Stephan Ewen
<se...@apache.org <mailto:se...@apache.org>> wrote:
>>> > Would have been great. I had high hopes when I saw the trick
with the
>>> > "constant pool", but this is only to make what Flink does
already
>>> > applicable
>>> > to non-serializable lambdas.
>>> >
>>> > If you want to help us with this, I'll ping you for some
support on the
>>> > OpenJDK mailing list ;-)
>>> >
>>> > On Tue, Aug 18, 2015 at 1:59 PM, Kristoffer Sjögren
<sto...@gmail.com <mailto:sto...@gmail.com>>
>>> > wrote:
>>> >>
>>> >> I suspected that you already had looked into this, but it
was worth a
>>> >> try. It would make everything so much easier.
>>> >>
>>> >> Thanks for the explanation :-)
>>> >>
>>> >>
>>> >> On Tue, Aug 18, 2015 at 1:50 PM, Stephan Ewen
<se...@apache.org <mailto:se...@apache.org>>
>>> >> wrote:
>>> >> > Hi Kristoffer!
>>> >> >
>>> >> > I looked through the code as well. In fact, Flink
currently uses the
>>> >> > trick
>>> >> > mentioned for Serializable Lambdas in the gist you sent me.
>>> >> >
>>> >> > This works well for lambdas that return simple types
(primitives or
>>> >> > classes
>>> >> > without generics). The information for the generic
parametrization
>>> >> > is
>>> >> > unfortunately really erased, it is in no signature or
anything.
>>> >> >
>>> >> > Java has the concept of "generic method signatures",
which means
>>> >> > that a
>>> >> > method gets a signature string that includes the generic
types.
>>> >> > These
>>> >> > signatures are generated for regular functions, but
OpenJDK and
>>> >> > OracleJDK do
>>> >> > not generate them for synthetic methods (like lambdas).
>>> >> >
>>> >> > We tried to submit a patch to OpenJDK to add these generic
>>> >> > signatures to
>>> >> > lambda methods, but they did not like the fact that we
try to figure
>>> >> > out
>>> >> > the
>>> >> > generic types of lambdas. I hope they change their minds
at some
>>> >> > point...
>>> >> >
>>> >> > Stephan
>>> >> >
>>> >> >
>>> >> >
>>> >> >
>>> >> > On Tue, Aug 18, 2015 at 11:46 AM, Aljoscha Krettek
>>> >> > <aljos...@apache.org <mailto:aljos...@apache.org>>
>>> >> > wrote:
>>> >> >>
>>> >> >> Unfortunately, this also doesn't work for the same
reasons. The
>>> >> >> generic
>>> >> >> types of generic parameters of a lambda are not stored
anywhere.
>>> >> >> Stephan
>>> >> >> mentioned to me that the only possibility right now
would be to
>>> >> >> look at
>>> >> >> the
>>> >> >> code using something like ASM to find a cast in the code
to the
>>> >> >> concrete
>>> >> >> type of the generic parameter.
>>> >> >>
>>> >> >> On Tue, 18 Aug 2015 at 11:35 Kristoffer Sjögren
<sto...@gmail.com <mailto:sto...@gmail.com>>
>>> >> >> wrote:
>>> >> >>>
>>> >> >>> How about https://github.com/jhalterman/typetools?
>>> >> >>>
>>> >> >>> On Tue, Aug 18, 2015 at 11:16 AM, Aljoscha Krettek
>>> >> >>> <aljos...@apache.org <mailto:aljos...@apache.org>>
>>> >> >>> wrote:
>>> >> >>> > Hi Kristoffer,
>>> >> >>> > I'm afraid not, but maybe Timo has some further
information. In
>>> >> >>> > this
>>> >> >>> > extended example we can see the problem:
>>> >> >>> >
https://gist.github.com/aljoscha/84cc363d13cf1dfe9364. The
>>> >> >>> > output
>>> >> >>> > is:
>>> >> >>> >
>>> >> >>> > Type is: class
>>> >> >>> > org.apache.flink.examples.java8.wordcount.TypeTest$Thing
>>> >> >>> > class
org.apache.flink.examples.java8.wordcount.TypeTest$Thing
>>> >> >>> > Type is: class
>>> >> >>> > org.apache.flink.examples.java8.wordcount.TypeTest$Thing
>>> >> >>> > class
org.apache.flink.examples.java8.wordcount.TypeTest$Thing
>>> >> >>> > Type is :
>>> >> >>> >
>>> >> >>> >
>>> >> >>> >
>>> >> >>> >
org.apache.flink.examples.java8.wordcount.TypeTest.org.apache.flink.examples.java8.wordcount.TypeTest$Thing<java.lang.String>
>>> >> >>> > class
org.apache.flink.examples.java8.wordcount.TypeTest$Thing
>>> >> >>> >
>>> >> >>> > So with the two lambda calls it does not correctly
determine the
>>> >> >>> > generic
>>> >> >>> > parameter of Thing while it works with the anonymous
class.
>>> >> >>> >
>>> >> >>> > I was exited when I saw the example because we've
been trying
>>> >> >>> > for so
>>> >> >>> > long to
>>> >> >>> > get this to work. Maybe we have to wait for java 19
to get this
>>> >> >>> > to
>>> >> >>> > work. ;-)
>>> >> >>> >
>>> >> >>> > Thanks a lot for helping, though. :D
>>> >> >>> > Aljoscha
>>> >> >>> >
>>> >> >>> > On Tue, 18 Aug 2015 at 11:01 Kristoffer Sjögren
>>> >> >>> > <sto...@gmail.com <mailto:sto...@gmail.com>>
>>> >> >>> > wrote:
>>> >> >>> >>
>>> >> >>> >> Hi
>>> >> >>> >>
>>> >> >>> >> Potential fix for writing flink jobs using lamdas
without
>>> >> >>> >> Eclipse
>>> >> >>> >> JDT?
>>> >> >>> >>
>>> >> >>> >>
https://gist.github.com/aslakhellesoy/3678beba60c109eacbe5
>>> >> >>> >>
>>> >> >>> >> Cheers,
>>> >> >>> >> -Kristoffer
>>> >> >
>>> >> >
>>> >
>>> >
>>
>>
>
