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I would like to eventually come back for named record patterns, but I think we have to let the dust settle first. <br class="">
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<div class="">On Apr 11, 2023, at 2:48 PM, Remi Forax <<a href="mailto:forax@univ-mlv.fr" class="">forax@univ-mlv.fr</a>> wrote:</div>
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<b class="">From:<span class="Apple-converted-space"> </span></b>"Robbe Pincket" <<a href="mailto:robbepincket@live.be" class="">robbepincket@live.be</a>><br class="">
<b class="">To:<span class="Apple-converted-space"> </span></b>"amber-dev" <<a href="mailto:amber-dev@openjdk.org" class="">amber-dev@openjdk.org</a>><br class="">
<b class="">Sent:<span class="Apple-converted-space"> </span></b>Monday, April 10, 2023 1:27:22 PM<br class="">
<b class="">Subject:<span class="Apple-converted-space"> </span></b>Named record patterns<br class="">
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<span lang="EN-US" class="">Hi all</span></div>
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<span lang="EN-US" class="">I was wondering if named record patterns `o instanceof Pair(String left, String right) pair` are still on the table for the future or not. (Not sure if 'named' record pattern is the right name?)</span></div>
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<div class="">Let re-state what is the issue, currently there is no way to create a binding capturing the whole record instance, forcing people to transform the record pattern to a type pattern + when (see below).<br data-mce-bogus="1" class="">
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<div class="">A previous preview was supporting this case using the syntax<br data-mce-bogus="1" class="">
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<div class=""> case Pair(String left, String right) pair -> ...<br data-mce-bogus="1" class="">
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<div class="">which did not work well in case someone want the binding to be also have an annotation or be declared final<br data-mce-bogus="1" class="">
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<div class="">Here is the previous syntax with "final"<br data-mce-bogus="1" class="">
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<div class=""> case final Pair(String left, String right) pair -> ...<br data-mce-bogus="1" class="">
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<div class="">which is not very readable, the "final" being too far apart from the binding.<br data-mce-bogus="1" class="">
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<div class="">One solution is to use a keyword like "as" to add a binding at the end of a record pattern (and perhaps other patterns ?)<br data-mce-bogus="1" class="">
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<div class=""> case Pair(String left, String right) as final pair -> ...</div>
<div class="">which as the advantage of grouping the binding and its keyword at the cost of adding a new keyword.<br data-mce-bogus="1" class="">
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<div class="">Rémi<br data-mce-bogus="1" class="">
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<span lang="EN-US" class="">IIRC they were shelfed due to the ambiguity that they could cause in this case, if there also exists a function `when`:</span></div>
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<span lang="EN-US" class="">```</span></div>
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<span lang="EN-US" class="">switch(o) {</span></div>
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<span lang="EN-US" class=""> case Pair(String left, String right) when when (left == right) -> ...</span></div>
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<span lang="EN-US" class="">}</span></div>
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<span lang="EN-US" class="">```</span></div>
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<span lang="EN-US" class="">It feels weird to me however that this feature was shelved just for this case, when a 'simple' rule could be introduced that a record pattern can't introduce a pattern variable with the name of a contextual keyword or at least not
`when`.</span></div>
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<span lang="EN-US" class="">Are there other reasons that record patterns can't introduce a variable that matches the whole pair anymore? It feels like it could be useful, even more so with JEP 443: Unnamed Patterns and Variables (Preview)</span></div>
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<span lang="EN-US" class="">```</span></div>
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<span lang="EN-US" class="">if (o instanceof ColoredPoint(Point(_, int y), _) cp && y > 0) {</span></div>
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<span lang="EN-US" class=""> doAction(cp);</span></div>
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<span lang="EN-US" class="">}</span></div>
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<span lang="EN-US" class="">```</span></div>
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<span lang="EN-US" class="">Instead of</span></div>
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<span lang="EN-US" class="">```</span></div>
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<span lang="EN-US" class="">if (o instanceof ColoredPoint(Point(int x, int y), Color c) && y > 0) {</span></div>
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<span lang="EN-US" class=""> doAction(new ColoredPoint(new Point(x, y), c));</span></div>
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<span lang="EN-US" class="">}</span></div>
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<span lang="EN-US" class="">```</span></div>
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<span lang="EN-US" class="">or this, if ColoredPoint can both hold `Point` and `Point3D`</span></div>
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<span lang="EN-US" class="">```</span></div>
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<span lang="EN-US" class="">if (o instanceof ColoredPoint cp && cp.point() instanceof Point(_, int y) && y > 0) {</span></div>
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<span lang="EN-US" class=""> doAction(cp);</span></div>
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<span lang="EN-US" class="">}</span></div>
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<span lang="EN-US" class="">```</span></div>
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<span lang="EN-US" class="">or if it can only hold `Point`</span></div>
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<span lang="EN-US" class="">```</span></div>
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<span lang="EN-US" class="">if (o instanceof ColoredPoint cp && cp.point().y() > 0) {</span></div>
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<span lang="EN-US" class=""> doAction(cp);</span></div>
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<span lang="EN-US" class="">}</span></div>
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<span lang="EN-US" class="">```</span></div>
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<span lang="EN-US" class="">Greetings</span></div>
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<span lang="EN-US" class="">Robbe Pincket</span></div>
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