> From: "Brian Goetz" <brian.go...@oracle.com>
> To: "Remi Forax" <fo...@univ-mlv.fr>, "Jesper Steen Møller"
> <jes...@selskabet.org>
> Cc: "Ilyas Selimov" <ilyas.seli...@jetbrains.com>, "amber-spec-experts"
> <amber-spec-experts@openjdk.java.net>
> Sent: Vendredi 3 Septembre 2021 22:07:57
> Subject: Re: Dominance in pattern matching for switch: Spec and Javac
> inconsistency
>>> If I understand correctly, a guarded switch label effectively can't
>>> dominate any
>>> other labels, since the spec doesn't go into trying to statically analyze
>>> whether or not the guard could ever be false.
>>> I guess the spec could mention that (but it would be a comment, since it
>>> follows
>>> from the other rules).
>> A guarded switch pattern can not dominate any other guarded switch pattern
>> that
>> have the same type pattern prefix,
>> e.g.
>> case Integer i && foo(i)
>> vs
>> case Integer i && bar(i)
>> but a guarded switch dominates it's prefix,
>> e.eg
>> case Integer i && foo(i) dominates case Integer.
> You've got that backwards; `Integer i` dominates `Integer i && g` for all g.
yes !
>> But there is no rule between a guarded pattern like case Integer i && foo(i)
>> and
>> case 1, so they can appear in any order.
> Correct, a type pattern `T` should dominate any constant case labels of type
> T,
> but you are right, thsi does not seem to work properly.
> Also doesn't work with 17ea:
> jshell> int x = 3; switch (x) { case Integer i:}
> x ==> 3
> | Error:
> | the switch statement does not cover all possible input values
> | switch (x) { case Integer i:}
> | ^---------------------------^
About the relation between int and Integer, the spec allows boxing but not
unboxing, i wonder if we enhance the spec to support unboxing,
unboxing being like a pattern query with two possible outcome: do not match if
null and match and extract the value if non null.
Integer anInteger = ...
switch(anInteger) {
case null -> // called if null
case int i -> // called for non null Integer
}
and
Integer anInteger = ...
switch(anInteger) { // NPE if null
case int i -> // called for non null Integer
}
with case Integer dominating case int.
Rémi
