<div><p style="font-size:50px;margin-top:0;margin-bottom:0">😱</p><p style="margin-top:10px;margin-bottom:0">David Alayachew reacted via <a href="https://www.google.com/gmail/about/?utm_source=gmail-in-product&utm_medium=et&utm_campaign=emojireactionemail#app">Gmail</a></p></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Wed, Jan 31, 2024 at 6:11 AM Brian Goetz <<a href="mailto:brian.goetz@oracle.com">brian.goetz@oracle.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><u></u>
<div>
<font size="4" face="monospace">I think you are probably thinking
about this in too few dimensions. For a one-dimensional problem:<br>
<br>
   sealed interface X permits A, B, C { }<br>
<br>
   switch (x) { <br>
       case A a -> <br>
       case B b -> ...<br>
   }<br>
<br>
it seems quite easy to "find the missing case."Â But here's an
only slightly harder one:<br>
<br>
   sealed interface A permits T, U { }<br>
   sealed interface B permits V, W { }<br>
   record R(A a, B b) { } <br>
<br>
   switch (r) {    <br>
       case R(A a, V b) -> ...    <br>
       case R(T a, _)  -> ...    <br>
   }<br>
<br>
What's missing? Well, there are any number of cases that can
complete the picture, such as<br>
<br>
    case R(U a, W b) -> ... <br>
 <br>
The problem gets harder fast as the dimensionality increases; R
has two components, both of which use sealing. And things scale
with not only the number of components, but the depth of sealed
hierarchies, etc. <br>
<br>
If you read the specification (or the precursor mathematical
model, an early version of which is here
(<a href="https://cr.openjdk.org/~briangoetz/eg-attachments/Coverage.pdf" target="_blank">https://cr.openjdk.org/~briangoetz/eg-attachments/Coverage.pdf</a>),
you'll see that it does not construct the full product space and
start "checking off boxes", so turning it into an example
generator (and keeping the two consistent) is not a small task. <br>
<br>
</font><br>
<div>On 1/30/2024 10:55 PM, David Alayachew
wrote:<br>
</div>
<blockquote type="cite">
<div dir="ltr">
<div class="gmail_default" style="font-family:monospace">Hello
Tagir,</div>
<div class="gmail_default" style="font-family:monospace"><br>
</div>
<div class="gmail_default" style="font-family:monospace">Thank
you for your response!</div>
<div class="gmail_default" style="font-family:monospace"><br>
</div>
<div class="gmail_default" style="font-family:monospace">Fair
point about NP-Complete. Maybe scaling back the idea would
make more sense.</div>
<div class="gmail_default" style="font-family:monospace"><br>
</div>
<div class="gmail_default" style="font-family:monospace">But I
am confused about this comment.<br>
</div>
<div class="gmail_default" style="font-family:monospace"><br>
</div>
<div class="gmail_default" style="font-family:monospace">>
From what I remember, it could be very non-trivial to
determine a minimal set of missing branches
</div>
<br>
<div class="gmail_default" style="font-family:monospace">I'm
very surprised to hear this, but if that is true, then let's
scale this down to the absolute minimum.</div>
<div class="gmail_default" style="font-family:monospace"><br>
</div>
<div class="gmail_default" style="font-family:monospace">In
order to know that we are missing a case, we must first find a
gap in the exhaustiveness, with respect to the remainder.</div>
<div class="gmail_default" style="font-family:monospace"><br>
</div>
<div class="gmail_default" style="font-family:monospace">So
let's move the goal posts and say that if we can report that
single type that is the gap, I would be happy enough with
that.</div>
<div class="gmail_default" style="font-family:monospace"><br>
</div>
<div class="gmail_default" style="font-family:monospace">Would
that be more realistic?</div>
<div class="gmail_default" style="font-family:monospace"><br>
</div>
<div class="gmail_default" style="font-family:monospace">Thank
you for reaching out!</div>
<div class="gmail_default" style="font-family:monospace">David
Alayachew<br>
</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Tue, Jan 30, 2024 at
3:21 AM Tagir Valeev <<a href="mailto:amaembo@gmail.com" target="_blank">amaembo@gmail.com</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div dir="ltr">IntelliJ IDEA can do this in simple cases (use
'Create missing branches' action in Alt+Enter menu on
"statement does not cover all possible input values" error
message). From what I remember, it could be very non-trivial
to determine a minimal set of missing branches in a general
case, especially if you have generic parameters and nested
deconstruction patterns. I'm not sure but probably it's an
NP-complete problem.
<div><br>
</div>
<div>With best regards,</div>
<div>Tagir Valeev.</div>
</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Tue, Jan 30, 2024 at
6:40 AM David Alayachew <<a href="mailto:davidalayachew@gmail.com" target="_blank">davidalayachew@gmail.com</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div dir="ltr">
<div class="gmail_default" style="font-family:monospace">Hello
Amber Dev Team,</div>
<div class="gmail_default" style="font-family:monospace"><br>
</div>
<div class="gmail_default" style="font-family:monospace">The
previous discussions on Checked Exceptions reminded me
about this.</div>
<div class="gmail_default" style="font-family:monospace"><br>
</div>
<div class="gmail_default" style="font-family:monospace">Is
there any possible future where sealed types will be
able to tell you which permitted subtypes are missing?</div>
<div class="gmail_default" style="font-family:monospace"><br>
</div>
<div class="gmail_default" style="font-family:monospace">This
is actually one of the sleeper features of Checked
Exceptions -- they don't just give you exhaustiveness,
they are even nice enough to tell you exactly which
Exception type you left out.</div>
<div class="gmail_default" style="font-family:monospace"><br>
</div>
<div class="gmail_default" style="font-family:monospace">This
is a godsend for maintenance, fearless refactoring,
and general correctness.</div>
<div class="gmail_default" style="font-family:monospace"><br>
</div>
<div class="gmail_default" style="font-family:monospace">Any
chance we could get this for sealed types in the
future?</div>
<div class="gmail_default" style="font-family:monospace"><br>
</div>
<div class="gmail_default" style="font-family:monospace">Thank
you for your time and help!</div>
<div class="gmail_default" style="font-family:monospace">David
Alayachew<br>
</div>
</div>
</blockquote>
</div>
</blockquote>
</div>
</blockquote>
<br>
</div>
</blockquote></div>