Hello!
Such kind of incompatibility happens every single time the new
supertype is introduced for two types. E.g., consider:
import java.lang.invoke.MethodType;
import java.util.List;
import java.io.Serializable;
class Main {
void test() {
MethodType mt = MethodType.methodType(void.class);
List<Serializable> list = List.of(mt, 1).subList(0,1);
}
}
Compilable in Java 11, not compilable in Java 12+
Test.java:8: error: incompatible types: List<INT#1> cannot be
converted to List<Serializable>
List<Serializable> list = List.of(mt, 1).subList(0,1);
^
where INT#1 is an intersection type:
INT#1 extends Object,Serializable,Constable
1 error
I don't think that such a compatibility issue was even mentioned in
Java 12 release notes.
With best regards,
Tagir Valeev.
On Wed, May 3, 2023 at 3:13 PM <fo...@univ-mlv.fr> wrote:
>
> Another example sent to me by a fellow French guy,
>
> final Deque<String> nestedDequeue = new ArrayDeque<>();
> nestedDequeue.addFirst("C");
> nestedDequeue.addFirst("B");
> nestedDequeue.addFirst("A");
>
> final List<String> nestedList = new ArrayList<>();
> nestedList.add("D");
> nestedList.add("E");
> nestedList.add("F");
>
> final List<Collection<String>> list = Stream.of(nestedDequeue,
> nestedList).toList();
>
> This one is cool because no 'var' is involved and using
> collect(Collectors.toList()) instead of toList() solves the inference problem.
>
> Rémi
>
> ----- Original Message -----
> > From: "Stuart Marks" <stuart.ma...@oracle.com>
> > To: "Remi Forax" <fo...@univ-mlv.fr>
> > Cc: "core-libs-dev" <core-libs-...@openjdk.java.net>
> > Sent: Tuesday, May 2, 2023 2:44:28 AM
> > Subject: Re: The introduction of Sequenced collections is not a source
> > compatible change
>
> > Hi Rémi,
> >
> > Thanks for trying out the latest build!
> >
> > I'll make sure this gets mentioned in the release note for Sequenced
> > Collections.
> > We'll also raise this issue when we talk about this feature in the Quality
> > Outreach
> > program.
> >
> > s'marks
> >
> > On 4/29/23 3:46 AM, Remi Forax wrote:
> >> I've several repositories that now fails to compile with the latest jdk21,
> >> which
> >> introduces sequence collections.
> >>
> >> The introduction of a common supertype to existing collections is *not* a
> >> source
> >> compatible change because of type inference.
> >>
> >> Here is a simplified example:
> >>
> >> public static void m(List<Supplier<? extends Map<String, String>>>
> >> factories) {
> >> }
> >>
> >> public static void main(String[] args) {
> >> Supplier<LinkedHashMap<String,String>> supplier1 = LinkedHashMap::new;
> >> Supplier<SortedMap<String,String>> supplier2 = TreeMap::new;
> >> var factories = List.of(supplier1, supplier2);
> >> m(factories);
> >> }
> >>
> >>
> >> This example compiles fine with Java 20 but report an error with Java 21:
> >> SequencedCollectionBug.java:28: error: method m in class
> >> SequencedCollectionBug
> >> cannot be applied to given types;
> >> m(factories);
> >> ^
> >> required: List<Supplier<? extends Map<String,String>>>
> >> found: List<Supplier<? extends SequencedMap<String,String>>>
> >> reason: argument mismatch; List<Supplier<? extends
> >> SequencedMap<String,String>>>
> >> cannot be converted to List<Supplier<? extends Map<String,String>>>
> >>
> >>
> >>
> >> Apart from the example above, most of the failures I see are in the unit
> >> tests
> >> provided to the students, because we are using a lot of 'var' in them so
> >> they
> >> work whatever the name of the types chosen by the students.
> >>
> >> Discussing with a colleague, we also believe that this bug is not limited
> >> to
> >> Java, existing Kotlin codes will also fail to compile due to this bug.
> >>
> >> Regards,
> > > Rémi
