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<p class="MsoNormal"><span lang="EN-US">Hi John,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">To be honest I never fully read the rules on when pattern values are in scope or not, and just always assumed it matches my mental model of ‘the variable is in scope if it would be definite assigned here assuming the
variable is definite assigned iff the match returned true’. <o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Using this assumption it is clear why this snippet wouldn’t work. `==` does not have any special rules about definite assignment when it’s arguments are boolean expressions and therefore falls back to the default of ‘A
variable is definite assigned after the execution of a boolean expression if it is definite assigned both when true and false’<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Hope this helps<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Kind regards<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Robbe Pincket</span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal" style="border:none;padding:0cm"><b>Van: </b><a href="mailto:hjohn@xs4all.nl">John Hendrikx</a><br>
<b>Verzonden: </b>donderdag 20 april 2023 9:21<br>
<b>Aan: </b><a href="mailto:amber-dev@openjdk.org">amber-dev</a><br>
<b>Onderwerp: </b>Variable not in scope after instanceof</p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Segoe UI",sans-serif">I came across a bit of a curious way to check if something is not an instance of something, and I noticed it doesn't play along with the new instanceof construct that allows
you to assign it to a local variable immediately:<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Segoe UI",sans-serif"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Segoe UI",sans-serif"> public static void main(String[] args) {
<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Segoe UI",sans-serif"> Number n = 1.0;
<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Segoe UI",sans-serif"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Segoe UI",sans-serif"> if (n instanceof Double d == false) {
<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Segoe UI",sans-serif"> System.out.println("It was not a double");
<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Segoe UI",sans-serif"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Segoe UI",sans-serif"> return;
<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Segoe UI",sans-serif"> }
<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Segoe UI",sans-serif"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Segoe UI",sans-serif"> System.out.println("It was a double: " + d); // compile error<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Segoe UI",sans-serif"> }<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Segoe UI",sans-serif"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Segoe UI",sans-serif">In the above snippet, the variable "d", despite being accepted, is not in scope anywhere.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Segoe UI",sans-serif"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Segoe UI",sans-serif">Changing the check to " !(n instanceof Double d)" works as expected.<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Segoe UI",sans-serif"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Segoe UI",sans-serif">Is this something that was missed, or am I misunderstanding why this can't work?<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Segoe UI",sans-serif"><o:p> </o:p></span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Segoe UI",sans-serif">--John<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Segoe UI",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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