Hi David,
> De: "Brian Goetz" <brian.go...@oracle.com>
> À: "amber-spec-experts" <amber-spec-experts@openjdk.java.net>
> Envoyé: Jeudi 1 Octobre 2020 22:33:28
> Objet: Fwd: Records feedback
> Received on the -comments list.
A Record does not support encapsulation (separating the public API and the
private implementation) given that it's a named tuple.
If you want encapsulation, use a class.
public class Nil<A> implements List<A> {
private static final Nil<?> INSTANCE = new Nil<Object>();
private Nil() {}
@SuppressWarnings("unchecked")
public <A> Nil<A> nil() { return (Nil<A>) INSTANCE; }
}
As a side note, i've also fixed your use of @SuppressWarnings("rawtypes") which
should be used mostly when dealing with code written before Java 5.
Here, you should use @SuppressWarnings("unchecked") to workaround the fact that
there is no type Nothing in Java and no way to express that Nil is covariant at
declaration site.
regards,
Rémi
> -------- Forwarded Message --------
> Subject: Records feedback
> Date: Thu, 1 Oct 2020 15:09:38 -0500
> From: David Aaron Kaye [ mailto:kayed...@gmail.com |
> <kayed...@gmail.com> ]
> To: [ mailto:java-se-spec-comme...@openjdk.java.net |
> java-se-spec-comme...@openjdk.java.net ]
> Good afternoon,
> I am very excited to see Records coming to Java. I have been playing around
> with them since JDK 14. I noticed that in the proposal, JDK-8246771
> [ https://bugs.openjdk.java.net/browse/JDK-8246771 |
> <https://bugs.openjdk.java.net/browse/JDK-8246771> ] , it says
> ...if the canonical constructor is explicitly declared then its access
> modifier must provide at least as much access as the record class
> I have implemented a functional List:
> public sealed interface List<A> permits Cons, Nil {
> }
> public record Cons<A>(A head, List<A> tail) implements List<A> {
> }
> @SuppressWarnings("rawtypes")
> public record Nil<Nothing>() implements List<Nothing> {
> public static final Nil instance = new Nil();
> private Nil() {
> }
> }
> I made the constructor private because I want this to be a singleton,
> accessed from instance, but the current proposal does not allow me to do
> that, and I get a compilation error on the private constructor. I could
> prefer to be able to make the constructor private so that I can have a
> record that is a singleton.
> Thanks,
> David Kaye
