> De: "Brian Goetz" <brian.go...@oracle.com> > À: "Remi Forax" <fo...@univ-mlv.fr> > Cc: "Gavin Bierman" <gavin.bier...@oracle.com>, "amber-spec-experts" > <amber-spec-experts@openjdk.java.net> > Envoyé: Vendredi 20 Septembre 2019 16:01:14 > Objet: Re: Draft JLS spec for JEP 305: Pattern matching for instanceof
> The rules for scoping outlined here > [ http://cr.openjdk.java.net/~briangoetz/amber/pattern-semantics.html | > http://cr.openjdk.java.net/~briangoetz/amber/pattern-semantics.html ] > certainly covered the propagation of binding variables through ternaries. And > those rules appear to be covered by 6.3.1.4 in Gavin’s draft. my bad, for whatever reason, i've not seen that section. > We value being able to freely refactor between the ternary expression and > if-statement forms; if you’ve got examples where that can’t be done, or where > the semantics and scoping differ, please point those out! Rémi >> On Sep 20, 2019, at 9:57 AM, Remi Forax < [ mailto:fo...@univ-mlv.fr | >> fo...@univ-mlv.fr ] > wrote: >> I don't remember if we have discuss this or not but if i read the spec >> correctly, >> there is no support for the operator ?: >> so a code like this is ok >> if (o instanceof String s) { >> return s.length(); >> } else { >> return 0; >> } >> while a code like this is not >> return (o instanceof String s)? s.length(): 0; >> supporting the "if statement" without supporting the "if expression" seems >> arbitrary given the duality of both constructs. >> Rémi >>> De: "Gavin Bierman" < [ mailto:gavin.bier...@oracle.com | >>> gavin.bier...@oracle.com ] > >>> À: "amber-spec-experts" < [ mailto:amber-spec-experts@openjdk.java.net | >>> amber-spec-experts@openjdk.java.net ] > >>> Envoyé: Jeudi 19 Septembre 2019 11:28:42 >>> Objet: Draft JLS spec for JEP 305: Pattern matching for instanceof >>> A draft language spec for JEP 305 (Pattern Matching for instanceof) is >>> available >>> at: >>> [ >>> http://cr.openjdk.java.net/~gbierman/jep305/jep305-20190918/specs/patterns-instanceof-jls.html >>> | >>> http://cr.openjdk.java.net/~gbierman/jep305/jep305-20190918/specs/patterns-instanceof-jls.html >>> ] >>> Comments are welcomed on all aspects, but I draw your attention to a couple >>> of >>> things that we’d like your feedback on: >>> 1. The instanceof operator restricts the type to be a reifiable reference >>> type. >>> The spec currently keeps that restriction for type test patterns too. But >>> should we go further, i.e. will people expect to be able to say the >>> following >>> (given that this *declares* a pattern variable l)? >>>> if (o instanceof List<Integer> l) { >>>> … >>>> } >>> 2. We’d like to keep the possibility open for merging of multiple pattern >>> declarations, where it makes sense. For example: >>>> if (a instanceof Foo f || b instanceof Foo f) { >>>> … // Like to be able to use f here >>>> } >>> The current spec explicitly calls out cases like these as compile-time >>> errors, >>> to allow for forwards compatibility if we add this feature. But what do you >>> think of this feature? (We have textually multiple declarations of a pattern >>> variable, but they are “merged”, so they are really the same thing…) >>> 3. [Only for spec nerds] I am proposing to add a new Chapter 16 to discuss >>> patterns (at the moment it’s short, but we’re planning for it to grow). The >>> existing Chapters 16-19 will be renumbered to 17-20. Will this renumbering >>> cause problems for anyone? >>> Thanks, >>> Gavin
