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<span style="background-color: rgb(255, 255, 255);">"if its a constant or an effectively final variable, otherwise you lose."</span></div>
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<span style="background-color: rgb(255, 255, 255);">Guards have the same requirements on variables so this seems logical to me.</span></div>
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<span style="background-color: rgb(255, 255, 255);">Kind regards</span></div>
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<span style="background-color: rgb(255, 255, 255);">Robbe Pincket</span></div>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>Van:</b> amber-spec-observers <amber-spec-observers-retn@openjdk.org> namens Brian Goetz <brian.goetz@oracle.com><br>
<b>Verzonden:</b> donderdag 4 april 2024 19:46<br>
<b>Aan:</b> Tagir Valeev <amaembo@gmail.com>; amber-spec-experts <amber-spec-experts@openjdk.org><br>
<b>Onderwerp:</b> Re: Exhaustiveness and instance patterns</font>
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<div class="PlainText">The examples I had worked out previously were all static patterns, so
<br>
this is a good one to work through.<br>
<br>
For an instance pattern use, we may or may not put some constraints on <br>
the receiver expression. I have an intuition that some sort of <br>
"effectively constant" constraint is useful, but I haven't fully worked <br>
through the details. But that's a separate concern.<br>
<br>
In your examples, I think we say that a set of instance patterns { <br>
x.p1(), x.p2() } are exhaustive if p1 and p2 form a complete set of case <br>
patterns, _and_ the receiver expressions `x` are provably the same. I <br>
think this amounts to "if its a constant or an effectively final <br>
variable, otherwise you lose."<br>
<br>
BTW, it is not just method invocations. If its a nonfinal field, it <br>
could be mutated by the p1() implementation (that would be very rude, <br>
but allowed).<br>
<br>
<br>
<br>
On 4/4/2024 1:29 PM, Tagir Valeev wrote:<br>
> Hello!<br>
><br>
> Suppose we declare several instance patterns and define that they form <br>
> an exhaustive set (using syntax from the bikeshed thread):<br>
><br>
> class X {<br>
> case pattern(String that) p1() {...}<br>
> case pattern(String that) p2() {...}<br>
> }<br>
><br>
> To match, we need an instance of type X. Could it be an arbitrary <br>
> expression, or it should be a limited thing (e.g., only a local <br>
> variable)? And how the exhaustiveness will be determined? E.g.:<br>
><br>
> X myX = ...<br>
> switch(str) {<br>
> case myX.p1() -> {...}<br>
> case myX.p2() -> {...}<br>
> }<br>
><br>
> Here, we can assume that the set of cases is exhaustive, because p1() <br>
> and p2() have the same effectively-final qualifier. But what if it's a <br>
> method call?<br>
><br>
> switch(str) {<br>
> case getX().p1() -> {...}<br>
> case getX().p2() -> {...}<br>
> }<br>
><br>
> The `getX()` method may return different instances of X, and it's not <br>
> evident anymore whether this set of patterns is exhaustive. Do we have <br>
> any strategy regarding this case? Or exhaustive sets are not allowed <br>
> for instance patterns?<br>
><br>
> With kind regards,<br>
> Tagir Valeev<br>
<br>
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