possible bug with instanceof pattern matching

[Charles]

Hi Brian

Thanks for clarifying. I suppose the second case, which uses two separate
variables, is also explained by that.

Since pattern matching doesn't differentiate which "je" got created, it
can't tell which variable will eventually be visible in the scope. Hence it
is saying both variables are not visible in the scope.




and as always, have a great day


*Best Regards*
*Charles*




On Sun, Feb 18, 2024 at 11:33 PM Brian Goetz <brian.goetz at oracle.com> wrote:

> This is not a bug; this potential feature was discussed at some length
> during the design process.  Another way this potential-feature could show
> up is:
>
>     switch (container) {
>         case Box(String s), Bag(String s): ... use s ...
>     }
>
> The reason that we chose not to proceed with such "binding merging" is
> that when you get inside the block, `je` is one variable with two
> declarations; you don't really know where the declaration is.  (So IDE
> navigations like "go to declaration" would have to learn to highlight TWO
> (or more) declarations, for example.)
>
> This feature isn't fundamentally impossible, and we could consider it
> again in the future, but it was a deliberate decision to not go this far at
> this time.
>
>
> On 2/18/2024 6:53 AM, Charles wrote:
>
> Hi all
>
>
> What I'm about to report below is *openjdk 17*.
>
>
> This doesn't compile
>
> if (ex instanceof JedisException je
>                             || (ex instanceof ExecutionException ee &&
> ee.getCause() instanceof JedisException je)
>             ){
>    ... blah blah
> }
>
> reason being the second je is already defined in the scope.
> [image: image.png]
>
> if you think about it. if ex is je, then, the second part won't trigger.
> And if the second part is reached, then ex is not je. Hence there is only
> going to be one statement mapped to je.
> no confusion here. I feel this should be allowed.
>
>
> Let's assume the above is the way it should be. I use different names for
> the second variable.
>
>  if (ex instanceof JedisException je
>                     || (ex instanceof ExecutionException ee &&
> ee.getCause() instanceof JedisException second_je)
>             ) {
>                 log.error(je);
>                 log.error(second_je);
>             }
>
> [image: image.png]
> This still doesn't compile.
>
> I would like to bring this issue up for discussion.
>
>
>
>
> and as always, have a great day
>
>
> *Best Regards *
> *Charles*
>
>
>
>
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