But if a failure to match throws a checked exception you _do_ have to
specifically ask for it. You still get exhaustiveness checking by default,
you will just see unintended assignment to a partial pattern surfaced as an
uncaught exception.
There's no need to introduce new `try-match` syntax to opt into assignment
to partial patterns, you can just lean on rules that users already
understand. You ask for it simply by catching or throwing the potential
exception.
try {
PartialPattern(var a) = blah;
} catch (MatchFailException e) {
}
Is that not sufficient?
On 16 January 2021 13:35:35 Brian Goetz <brian.go...@oracle.com> wrote:
Hah, synchronicity! Yes, I was drafting an email with a suggestion for
something similar, although i used a __MATCH_OR_DIE expression form
that looked like a cast, and an unchecked exception.
Did I just imagine it, or was there a suggestion for something like
this in the past?:
var Point(var x, var y) = ...
Close. We have experimented with various forms of "imperative match".
Our first attempt was something like:
let P = e;
where P had to be total. This was later refined to something like
let P = e
else { ... }
where the else block had to either throw, or assign to all the bindings
in the pattern.
We later started to feel that (a) `let` was unnecessarily fussy, and (b)
casting it like a statement meant that we lost some other
opportunities. So we shifted towards something like
P = e
for suitably constrained patterns, on the observation that
T t = e;
which is currently a local variable assignment, could equally well be
interpreted as matching the type pattern `T t` to the expression. So we
could retroactively reinterpret `P = e` (at least for type and
deconstruction patterns) as an imperative match, rather than a
declaration-with-initializer, if we want. That's nice, but that kind of
forecloses on the else clause.
Regardless, the semantics here would be match-or-not, rather than
match-or-die. I think if you wanted match-or-die, you'd have to
specifically ask for it somehow (such as a try- construct.)
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