possible bug with instanceof pattern matching

[Brian Goetz]

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.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.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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