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" <gavin.bier...@oracle.com>
> À: "amber-spec-experts" <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
