----- Mail original ----- > De: "John Rose" <john.r.r...@oracle.com> > À: "Remi Forax" <fo...@univ-mlv.fr> > Cc: "valhalla-spec-experts" <valhalla-spec-experts@openjdk.java.net> > Envoyé: Jeudi 9 Mai 2019 00:50:10 > Objet: Re: It's not safe until it's in the coffer
> On May 8, 2019, at 3:12 PM, Remi Forax <fo...@univ-mlv.fr> wrote: >> >> I propose to use Coffer<Complex> instead of Complex? (with Complex an inline >> class). > > So you are giving a name, "Coffer", to the Old Contract. > > The javadoc for the named type-constructor could describe > this contract fully: > > - array performance profile associated with indirections not inlines > - non-tearing indirection-based updates > - null in the value set, if the inline type is already null natively > - L-descriptors in the JVM (for those who peek) > - circularities OK (a Foo can have a field of type Coffer<Foo>) > > Maybe Indirect<VT> is the right name, then? it's better than Coffer. > > The effect of doing this would be to make the indirect version > of a type VT to look superficially more like a box, at a time > when we are trying to downplay boxes. But it's only superficial. yes > > The Coffer/Indirect generic is a one-off type constructor, > like ? itself. Put another way, matchfix C<.> is just a bulkier > syntax for postfix-? As such it would have to be documented > in its essence in the JLS, as well as in its javadoc. > > One consequence of Coffer/Indirect is that it puts a larger > distance between the two types than VT -vs- VT? does. > In that, it's sort of like Integer-vs-int. But unlike boxes, > natural VT operations are not lifted to Coffer<VT>. > The difference between VT and VT? is small enough > that I (for one) would expect operations on VT to be > lifted to VT?. We would also expect a type system > relation between VT and VT?. > > A consequence of bulkier notation is that it's clear that > VT <: C<VT> is false. Another is that programmers > will think twice before saying C<VT> where VT? could be > an attractive nuisance (like the register keyword). yes > > So, there are some things to like about this bulky syntax. > There are lots to dislike: > > - it's bulky (bug or feature?) > - the nullability is less obvious (but maybe that's not a problem) > - it's a one-off that has to be defined in JLS and javadoc both > - it will remind us of wrappers, sometimes for the nullability, given that Indirect is not an inline class but an indirect class, i don't think this is an issue. > > — John > > P.S. BTW, would Coffer<?> erase to Object? It can be but i was not able to find that useful given that V is already a subtype of Object and erasing instanceof Indirect<?> to instanceof Object is surprising. > > P.P.S. Must… not… mention… covfefe… argh!!! i hope my proposal will not gone covfefe :) Rémi
