> On Aug 31, 2020, at 7:35 AM, Brian Goetz <brian.go...@oracle.com> wrote:
>
> Totality is a term that language designers like, but may not be all that
> evocative to users. So switch-total might not exactly turn on the light bulb
> for them. In this manner, “sealed” has a useful connotation that has nothing
> to do with sealed types: non-leakiness: a sealed switch doesn’t leak any
> unprocessed values!
>
> Test driving ...
>
> sealed switch (x) { … }
> sealed-switch (x) { … }
> switch-sealed (x) { … }
>
> “A switch may be sealed with the sealed modifier; expression switches are
> implicitly sealed. The set of case patterns for a sealed switch must be
> total with some remainder; synthetic throwing cases are inserted for the
> remainder.”
+1
I like this being up front. I find tricks embedded in the body like 'default:
unreachable' do be too subtle and verbose. And I like the reuse of 'sealed'.
It's unclear whether your "some remainder" is allowed to be empty. (There was
some discussion earlier about outlawing 'default' in the equivalent of a sealed
switch.) I hope full totality is fine—an expression switch, implicitly
'sealed', of course permits a 'default' clause.
And then note that, given the existence of 'sealed switch', the 'default Object
o' feature is redundant. If you want to make sure you have a total case in your
switch, just say 'sealed' at the top. All sealed switches (both statement and
expression) guarantee either optimistic totality + NPE or that the last clause
is total.
