Expression switch exception naming

Brian Goetz brian.goetz at
Fri Mar 30 18:44:23 UTC 2018

I'm not talking about recovering.  This is purely taxonomy; this sort of 
mismatch does not (IMO) rise to the level of Error.

On 3/30/2018 2:42 PM, Remi Forax wrote:
> You still have not explain why you want to recover from one of these exception knowning that it's simpler to add a default if you want to take care of an unknown enum constant.
> Rémi
> ----- Mail original -----
>> De: "Brian Goetz" <brian.goetz at>
>> À: "Kevin Bourrillion" <kevinb at>
>> Cc: "amber-spec-experts" <amber-spec-experts at>
>> Envoyé: Vendredi 30 Mars 2018 20:39:30
>> Objet: Re: Expression switch exception naming
>>> All right, I've been focusing too much on the hierarchy, but the
>>> leaf-level name is more important than that (and the message text
>>> further still, and since I assume we'll do a fine job of that, I can
>>> probably relax a little). To answer your question, sure, the "ICC" is
>>> a pretty decent signal. Have we discussed Cyrill's point on -observers
>>> that we should create more specific exception types, such as
>>> UnrecognizedEnumConstantE{rror,xception}?
>> Yes.  What I'd been proposing was something like:
>> class IncompatibleClassChangeException <: Exception
>> or
>> classUnexpectedClassChangeException <: Exception
>> and then
>> UnexpectedEnumConstantException <: {I,U}CCE
>> UnexpectedSealedTypeException <: {I,U}CCE
>>> Okay, that is a sane approach, but I think it leaves too much of the
>>> value on the floor. I often benefit from having my exhaustiveness
>>> validated and being able to find out at compile time if things change
>>> in the future.
>> To be clear, I was describing:
>>   - We'd always do exhaustiveness checking for expression switches
>>   - A default / total pattern always implies exhaustive
>>   - We'd additionally consider an expression switch to be exhaustive if
>> all known enums are present _and_ the enum type is in the same module as
>> the switch
>> But that's probably too fussy.

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