<html><body><div style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000"><div><br></div><div><br></div><hr id="zwchr" data-marker="__DIVIDER__"><div data-marker="__HEADERS__"><blockquote style="border-left:2px solid #1010FF;margin-left:5px;padding-left:5px;color:#000;font-weight:normal;font-style:normal;text-decoration:none;font-family:Helvetica,Arial,sans-serif;font-size:12pt;"><b>From: </b>"Viktor Klang" <viktor.klang@oracle.com><br><b>To: </b>"Remi Forax" <forax@univ-mlv.fr><br><b>Sent: </b>Wednesday, January 17, 2024 6:01:38 PM<br><b>Subject: </b>Re: Seing a Collector as a Gatherer<br></blockquote></div><div><style style="display:none;"> P {margin-top:0;margin-bottom:0;} </style></div><div data-marker="__QUOTED_TEXT__"><blockquote style="border-left:2px solid #1010FF;margin-left:5px;padding-left:5px;color:#000;font-weight:normal;font-style:normal;text-decoration:none;font-family:Helvetica,Arial,sans-serif;font-size:12pt;">
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Hi Rémi,</div>
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Yes, this was something I was hoping to get into the preview, but I wasn't sure where that conversion should end up.</div>
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There are a few different places where it might go:<br>
<br>
Gatherer.of(Collector)<br>
Gatherers.collect(Collector)</div>
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Collector.asGatherer()</div>
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Collectors.gather(Collector)</div>
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I wasn't really convinced where it should go, and I was hesitant to making any changes to existing public interfaces as a "nice to have", so I opted to leave it out for now.</div>
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I think people would prefer to see it on Collector as a default method, but as I said before, making changes to Collector wasn't something I was ready to prioritize for the (first) JEP.</div></blockquote><div><br></div><div>I think this method is also important pedagogically, there should be a place that describe the relationship between a Collector and a Gatherer.<br data-mce-bogus="1"></div><div><br data-mce-bogus="1"></div><div>For Gatherer.of(), this one seems alien compared to the other overloads of of()/ofSequential() and to a lesser extend I do not like too much to have overloads with one parameter with two different interfaces, because someone can comes with a class that implements both Collector and Integrator (as stupid as it is),<br data-mce-bogus="1"></div><div><br data-mce-bogus="1"></div><div>For Gatherers.collect(Collector) is fine,<br data-mce-bogus="1"></div><div><br data-mce-bogus="1"></div><div>For Collector.asGatherer(), a default method has the disadvantage that usually a Collector is typed from left to right so calling an instance method requires an intermediary variable<br data-mce-bogus="1"></div><div> Collector<String, ?, List<String>> collector = Collector.toList(); // ok<br data-mce-bogus="1"></div><div> Gatherer<String, ?, List<String>> gatherer = Collector.toList().asGatherer(); // we are in trouble here<br data-mce-bogus="1"></div><div> that's why Collectors.collectingAndThen() (aka compose the finisher) is a static method in Collectors and not an instance method in Collector (finishAndThen ?),</div><div><br data-mce-bogus="1"></div><div>For Collectors.gather(), methods inside Collectors tend to return a Collector.<br data-mce-bogus="1"></div><div><br data-mce-bogus="1"></div><div><br data-mce-bogus="1"></div><blockquote style="border-left:2px solid #1010FF;margin-left:5px;padding-left:5px;color:#000;font-weight:normal;font-style:normal;text-decoration:none;font-family:Helvetica,Arial,sans-serif;font-size:12pt;"><div class="elementToProof" style="font-family: Aptos, Aptos_EmbeddedFont, Aptos_MSFontService, Calibri, Helvetica, sans-serif; font-size: 12pt; color: rgb(0, 0, 0);"><br>
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Cheers,<br>
√</div></div></blockquote><div><br></div><div>regards,<br data-mce-bogus="1"></div><div>Rémi<br data-mce-bogus="1"></div><div><br data-mce-bogus="1"></div><blockquote style="border-left:2px solid #1010FF;margin-left:5px;padding-left:5px;color:#000;font-weight:normal;font-style:normal;text-decoration:none;font-family:Helvetica,Arial,sans-serif;font-size:12pt;"><div id="Signature">
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<b><br></b></div>
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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 Remi Forax <forax@univ-mlv.fr><br><b>Sent:</b> Wednesday, 17 January 2024 17:08<br><b>To:</b> core-libs-dev <core-libs-dev@openjdk.java.net><br><b>Subject:</b> Seing a Collector as a Gatherer</font>
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<div class="BodyFragment"><font size="2"><span style="font-size:11pt;"><div class="PlainText">Hello,<br>
I may have overlook that, but it seems there is no method to see a Collector as a Gatherer.<br>
<br>
A Gatherer is more general than a Collector and a Gatherer with a greedy integrator that does not call Downstream.push in the intergator and only once is the finisher is basicaly a Collector.<br>
<br>
In code:<br>
<E, A, T> Gatherer<E, A, T> asGatherer(Collector<? super E, A, ? extends T> collector) {<br>
var supplier = collector.supplier();<br>
var accumulator = collector.accumulator();<br>
var combiner = collector.combiner();<br>
var finisher = collector.finisher();<br>
return Gatherer.of(supplier,<br>
Gatherer.Integrator.ofGreedy((state, element, _) -> {<br>
accumulator.accept(state, element);<br>
return true;<br>
}),<br>
combiner,<br>
(state, downstream) -> downstream.push(finisher.apply(state)));<br>
}<br>
<br>
This is eaxctly how Gatherer.fold() works.<br>
<br>
Is there a reason why such method does not exist ?<br>
<br>
regards,<br>
Rémi<br>
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