> From: "Viktor Klang" <viktor.kl...@oracle.com>
> To: "Remi Forax" <fo...@univ-mlv.fr>, "core-libs-dev"
> <core-libs-...@openjdk.java.net>
> Sent: Wednesday, January 17, 2024 5:49:01 PM
> Subject: Re: Gatherer API : wildcards complaint
> Hi Rémi,
> Thank you for the feedback—examples would be much appreciated!
Here is an example with an interface and a class,
interface Counter {
void increment ();
int value ();
}
Gatherer < String , Counter , Integer > count () {
class CounterImpl implements Counter {
int counter ;
@Override
public void increment () {
counter ++;
}
@Override
public int value () {
return counter ;
}
}
Supplier < CounterImpl > initializer = CounterImpl :: new ;
Gatherer . Integrator < Counter , String , Gatherer . Downstream <? super
Integer >> integrator = ( counter , _ , _ ) -> {
counter .increment();
return true ;
};
BiConsumer < Counter , Gatherer . Downstream <? super Integer >> finisher = (
counter , downstream ) -> {
downstream .push( counter .value());
};
return Gatherer . ofSequential ( initializer , integrator , finisher ); // does
not compile :(
}
void main () {
System . out .println( Stream . of ( "foo"
).gather(count()).findFirst().orElseThrow());
}
if instead of explicitly typing each functions, we directly call ofSequential,
it works
return Gatherer . ofSequential (
CounterImpl :: new ,
( Counter counter , String _ , Gatherer . Downstream <? super Integer > _ ) ->
{
counter .increment();
return true ;
},
( Counter counter , Gatherer . Downstream <? super Integer > downstream ) -> {
downstream .push( counter .value());
}
);
because here, CounterImpl::new is inferred as Supplier<Counter>.
> Cheers,
> √
> Viktor Klang
> Software Architect, Java Platform Group
> Oracle
> From: core-libs-dev <core-libs-dev-r...@openjdk.org> on behalf of Remi Forax
> <fo...@univ-mlv.fr>
> Sent: Wednesday, 17 January 2024 16:55
> To: core-libs-dev <core-libs-...@openjdk.java.net>
> Subject: Gatherer API : wildcards complaint
> Hello,
> this is a minor complaint but I do not see a raison to not getting this right.
> Currently the Gatherer API does not use the wildcard correctly, which is not
> fully an issue because there is "enough" wildcards that if you rely on the
> inference, it will work.
> The problem is that when you write code, you make mistakes and usually when
> you
> have a typing issue, a way to debug it is to fix the type arguments
> de-activating the inference.
> But because there are some missing wildcards, this debugging strategy just
> fail
> flat with more typing errors.
> I think that fixing the missing wildcards will hep users (or a least me) to
> have
> a better experience when using the Gatherer API.
> I can help and propose a PR if you want.
> regards,
> Rémi
