To be clear, I think the sweet spot here is:
- Legacy enum, string, and box (ESB) switches continue to throw NPE on
null;
- Total switches on enum (including the current expression switches on
enum) throw ICCE on a novel value;
- For new switches with remainder:
- Continue to throw NPE on unhandled null remainder;
- Throw UnexpectedFrogException on any other unhandled remainder.
On 8/28/2020 9:18 PM, Brian Goetz wrote:
And for all this complex analysis we get... some different exception
types? Doesn't seem like a worthwhile trade.
As I've mentioned already, I think the exception-type thing is mostly
a red herring. We have some existing precendent, which is pretty hard
to extrapolate from:
- Existing switches on enum/string/boxes throw NPE on a null target;
- (As of 12) enum expression switches throw ICCE when confronted with
a novel value.
All the discussion about exception types are trying to extrapolate
from these, but it's pretty hard to actually do so. I would be happy
to just have some sort of SwitchRemainderException.
What I'd like to do instead: switch expressions that are
optimistically/weakly total get an implicit 'default' case that
throws 'UnmatchedSwitchException' or something like that for
*everything* that goes unhandled. Exactly what diagnostic information
we choose to put in the exception is a quality of implementation
issue. As a special case, if the unmatched value is 'null' (not
'Box(null)'), we *might* decide to throw an NPE instead (depending on
how your ideas about null hostility in switches pan out)
That is, essentially, what I have proposed in my "Totality" thread (I
suspect you're still catching up, as it took us a long time to get
there.)
This is a behavioral change for enum switch expressions in Java 14+
code, which makes me feel a bit sheepish, but I don't think anybody
will mind a change now that the design has evolved enough to
recognize the need for a specific exception class.
I don't think we need an incompatible change; we're already sealing
off some legacy behavior with enum/string/box switches, we can seal
this one off there too.
