[patterns] Several patterns and guards

[Tagir Valeev]

> And also the formatting does not help, you can compare

Of course, if you know the confusing semantics of the language, you
can format the code to make it less confusing. We can also provide IDE
warnings or autoformatting to help the users to avoid confusion. But
it's always better to make the language non-confusing in the first
place.

With best regards,
Tagir Valeev.

>
> void test(Object obj) {
>   switch (obj) {
>     case Integer _,
>          String _ when !((String) obj).isEmpty()
>             -> System.out.println("Number or non-empty string");
>     default -> System.out.println("other");
>   }
> }
>
> with
>
> void test(Object obj) {
>   switch (obj) {
>     case Integer _, String _
>       when !((String) obj).isEmpty()
>             -> System.out.println("Number or non-empty string");
>     default -> System.out.println("other");
>   }
> }
>
> I think that if a comma is used in a "case", the "when" should be moved to the next line to make the semantics more obvious.
>
> Rémi
>
> >
> >> On Aug 14, 2023, at 5:15 AM, Tagir Valeev <amaembo at gmail.com> wrote:
> >>
> >> Hello!
> >>
> >> Currently, when the switch label contains several patterns, only one
> >> guard could be declared, which is applied to all the patterns at once.
> >> In other words, the following code is not possible:
> >>
> >> void test(Object obj) {
> >>  switch (obj) {
> >>    case Integer _ when ((Integer) obj) > 0,
> >>         String _ when !((String) obj).isEmpty()
> >>            -> System.out.println("Positive number or non-empty string");
> >>    default -> System.out.println("other");
> >>  }
> >> }
> >>
> >> Does it make sense to lift this restriction? Probably it could be
> >> useful to declare separate guards? Ideally it should be possible to be
> >> able to declare a pattern variable, which is visible inside the
> >> pattern-specific guard only (but not inside the rule body).
> >>
> >> Another confusing thing here:
> >>
> >> void test(Object obj) {
> >>  switch (obj) {
> >>    case Integer _,
> >>         String _ when !((String) obj).isEmpty()
> >>            -> System.out.println("Number or non-empty string");
> >>    default -> System.out.println("other");
> >>  }
> >> }
> >>
> >> Now, the guard is applied even if obj is Integer (resulting in
> >> ClassCastException). This is not quite evident from the code. We may
> >> say that 'when' precedence is lower than ',' precedence, but people
> >> may expect the opposite. Should not we reconsider this and make guard
> >> a part of the lebel element, rather than the part of the whole label?
> >>
> >> With best regards,
> > > Tagir Valeev.