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The challenge here is that there is no, current, reification of a pattern application, so all it boils down to at this point is: given a Predicate for some type T, make a cast to some unrelated type R.</div>
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For Class-based retention of elements, it is possible to do the equivalent of testing Class::isInstance(element) and then push the element downstream after a Class::cast(element)</div>
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Cheers,<br>
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<b>Viktor Klang</b></div>
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Software Architect, Java Platform Group<br>
Oracle</div>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> core-libs-dev <core-libs-dev-retn@openjdk.org> on behalf of Nir Lisker <nlisker@gmail.com><br>
<b>Sent:</b> Saturday, 26 April 2025 20:55<br>
<b>To:</b> core-libs-dev@openjdk.org <core-libs-dev@openjdk.org><br>
<b>Subject:</b> Casting gatherer</font>
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<div dir="ltr">Hi,
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<div>instanceof has been refitted to include an auto-cast ("pattern matching on instanceof"). Unfortunately, doing this as an intermediate operation on a stream requires first to filter via instanceof and then map via a cast. This is because</div>
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<div> x instanceof MyClass myClass</div>
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<div>returns a boolean, not myClass.</div>
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<div>I've asked for an easier way of doing it long ago directly on Stream and was declined, but now with Gatherers I'm bringing this up again. I think it would be reasonable to put such an operation in the Gatherers class. I imagine that many Gatherer libraries,
or utility classes, will include it since it's a common operation, and having it in the JDK means that it'll be done the best way possible (you can optimize where others can't, if applicable here).</div>
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<div>-- Nir</div>
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