> From: "Brian Goetz" <brian.go...@oracle.com> > To: "Remi Forax" <fo...@univ-mlv.fr> > Cc: "Dan Heidinga" <heidi...@redhat.com>, "Kevin Bourrillion" > <kev...@google.com>, "valhalla-spec-experts" > <valhalla-spec-experts@openjdk.java.net> > Sent: Monday, April 25, 2022 9:54:26 PM > Subject: Re: [External] Foo / Foo.ref is a backward default; should be > Foo.val / > Foo
>> This seems very specific to Optional, for Optional storing null is always a >> mistake, but that's not true for other VBC, by example a deadline can be >> typed >> as an Instant with null meaning no deadline. > No, it is not specific to Optional at all. Many domains exclude null on an > ad-hoc basis. > It is about giving the user the choice to reserve space in the heap for the > null > or not. If other logic has already excluded null (which is common), they can > use an Instant.val and get better footprint. If they like the semantics of > having null, they can use Instant. As the maintainer of Instant, you do not want people to be able to misuse your API, if you declare Instant as a B3, then they will see the tearing, so you will declare it as a B2 so the whole point of having B3 being a ref by default is moot. Optional is special not only because null make no sense but also because it's size is small enough to be loaded/stored in one (micro-)instruction. Rémi
