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<font size="4"><font face="monospace">This one got stuck in the
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<th valign="BASELINE" nowrap="nowrap" align="RIGHT">Subject:
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<td>Use of "assignment compatible" in the switch statement
specifications</td>
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<th valign="BASELINE" nowrap="nowrap" align="RIGHT">Date: </th>
<td>Wed, 6 Jul 2022 22:29:32 +0000</td>
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<th valign="BASELINE" nowrap="nowrap" align="RIGHT">From: </th>
<td>Robbe Pincket <a class="moz-txt-link-rfc2396E" href="mailto:robbepincket@live.be"><robbepincket@live.be></a></td>
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<th valign="BASELINE" nowrap="nowrap" align="RIGHT">To: </th>
<td><a class="moz-txt-link-abbreviated" href="mailto:jls-jvms-spec-comments@openjdk.java.net">jls-jvms-spec-comments@openjdk.java.net</a>
<a class="moz-txt-link-rfc2396E" href="mailto:jls-jvms-spec-comments@openjdk.java.net"><jls-jvms-spec-comments@openjdk.java.net></a>,
<a class="moz-txt-link-abbreviated" href="mailto:amber-spec-comments@openjdk.org">amber-spec-comments@openjdk.org</a>
<a class="moz-txt-link-rfc2396E" href="mailto:amber-spec-comments@openjdk.org"><amber-spec-comments@openjdk.org></a></td>
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<p class="MsoNormal"><span lang="EN-GB">Hi experts<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">A while back I was
reading the new amber spec on switch pattern matching, and
read something that felt off, but after checking the normal
spec, I noticed the issue existed there too.
<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">It was late when I sent
my review of the amber spec to their group, so I wanted to
sent this the day after but I managed to forget it.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">In 5.2, the concept of
"assignment compatible" is introduced:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">> If the type of an
expression can be converted to the type of a variable by
assignment conversion, we say the expression (or its value)
is assignable to the variable or, equivalently, that the
type of the expression is assignment compatible with the
type of the variable.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">It is a useful concept
that is used a total of 16 times in the spec for java 18
(and the current 19 spec).<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Although this concept is
introduced as a relation between two types, in the switch
statement specifications (14.11) the following appears:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">> 14.11.1 Switch
Blocks<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">> ...<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">> The switch block of
a switch statement or a switch expression is compatible with<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">the type of the selector
expression, T, if both of the following are true:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">> * If T is not an
enum type, then **every case constant associated with the
switch<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">block is assignment
compatible with T (ยง5.2)**.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">> * ...<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Here the relation is
used between a constant and a type, which seems to be
incorrect.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">For the Amber experts,
this section has been rewritten due to there being more
valid possible selector types, but the issue remains:<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">> A case constant c
is switch compatible with a type T where T is either char,
byte, short, int, Character, Byte, Short, Integer, or String
if c is assignment compatible with T (5.2).<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Greetings<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-GB">Robbe Pincket</span><span lang="EN-GB"><o:p></o:p></span></p>
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