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New issue from Ruslan Arutyunyan: "Missing permutable constraint for iterator overloads in Parallel Range Algorithms"
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‎xml/issue4297.xml‎

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<?xml version='1.0' encoding='utf-8' standalone='no'?>
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<!DOCTYPE issue SYSTEM "lwg-issue.dtd">
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<issue num="4297" status="New">
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<title>Missing `permutable` constraint for iterator overloads in Parallel Range Algorithms</title>
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<section><sref ref="[algorithm.syn]"/><sref ref="[alg.remove]"/><sref ref="[alg.partitions]"/></section>
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<submitter>Ruslan Arutyunyan</submitter>
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<date>27 Jun 2025</date>
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<priority>99</priority>
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<discussion>
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<p>
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The <paper num="P3179R9"/>: Parallel Range Algorithms paper was accepted to C++ working draft for C++ 26.
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Unfortunately, there is an oversight for three algorithms &mdash; `remove`, `remove_if` and `partition` &mdash;
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where the `permutable` constraint is missing. This applies to "Iterator and Sentinel" overloads only. The
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issue exists in <sref ref="[algorithm.syn]"/> as well as in per-algorithm sections:
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<sref ref="[alg.partitions]"/> and <sref ref="[alg.remove]"/>.
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</p>
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</discussion>
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<resolution>
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<p>
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This wording is relative to this
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<a href="https://github.com/cplusplus/draft/actions/runs/16433597877/artifacts/3583518547">CD preview draft</a>.
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</p>
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<ol>
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<li><p>Modify <sref ref="[algorithm.syn]"/>, header <tt>&lt;algorithm&gt;</tt>, as indicated:</p>
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<blockquote>
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<pre>
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[&hellip;]
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template&lt;<i>execution-policy</i> Ep, random_access_iterator I, sized_sentinel_for&lt;I&gt; S,
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class Proj = identity, class T = projected_value_t&lt;I, Proj&gt;&gt;
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requires <ins>permutable&lt;I&gt; &amp;&amp;</ins>
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indirect_binary_predicate&lt;ranges::equal_to, projected&lt;I, Proj&gt;, const T*&gt;
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subrange&lt;I&gt; remove(Ep&amp; exec, I first, S last, const T&amp; value,
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Proj proj = {}); <i>// freestanding-deleted</i>
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template&lt;<i>execution-policy</i> Ep, <i>sized-random-access-range</i> R, class Proj = identity,
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class T = projected_value_t&lt;iterator_t&lt;R&gt;, Proj&gt;&gt;
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requires permutable&lt;iterator_t&lt;R&gt;&gt; &amp;&amp;
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indirect_binary_predicate&lt;ranges::equal_to,
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projected&lt;iterator_t&lt;R&gt;, Proj&gt;, const T*&gt;
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borrowed_subrange_t&lt;R&gt;
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remove(Ep&amp;&amp; exec, R&amp;&amp; r, const T&amp; value, Proj proj = {}); <i>// freestanding-deleted</i>
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[&hellip;]
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template&lt;<i>execution-policy</i> Ep, random_access_iterator I, sized_sentinel_for&lt;I&gt; S,
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class Proj = identity, indirect_unary_predicate&lt;projected&lt;I, Proj&gt;&gt; Pred&gt;
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<ins>requires permutable&lt;I&gt;</ins>
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subrange&lt;I&gt;
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remove_if(Ep&amp; exec, I first, S last, Pred pred, Proj proj = {}); <i>// freestanding-deleted</i>
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template&lt;<i>execution-policy</i> Ep, <i>sized-random-access-range</i> R, class Proj = identity,
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indirect_unary_predicate&lt;projected&lt;iterator_t&lt;R&gt;, Proj&gt;&gt; Pred&gt;
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requires permutable&lt;iterator_t&lt;R&gt;&gt;
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borrowed_subrange_t&lt;R&gt;
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remove_if(Ep&amp; exec, R&amp; r, Pred pred, Proj proj = {}); <i>// freestanding-deleted</i>
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[&hellip;]
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template&lt;execution-policy Ep, random_access_iterator I, sized_sentinel_for&lt;I&gt; S,
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class Proj = identity, indirect_unary_predicate&lt;projected&lt;I, Proj&gt;&gt; Pred&gt;
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<ins>requires permutable&lt;I&gt;</ins>
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subrange&lt;I&gt;
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partition(Ep&amp;&amp; exec, I first, S last, Pred pred, Proj proj = {}); <i>// freestanding-deleted</i>
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template&lt;<i>execution-policy</i> Ep, <i>sized-random-access-range</i> R, class Proj = identity,
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indirect_unary_predicate&lt;projected&lt;iterator_t&lt;R&gt;, Proj&gt;&gt; Pred&gt;
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requires permutable&lt;iterator_t&lt;R&gt;&gt;
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borrowed_subrange_t&lt;R&gt;
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partition(Ep&amp;&amp; exec, R&amp;&amp; r, Pred pred, Proj proj = {}); <i>// freestanding-deleted</i>
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[&hellip;]
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</pre>
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</blockquote>
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</li>
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<li><p>Modify <sref ref="[alg.remove]"/> as indicated:</p>
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<blockquote>
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<pre>
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[&hellip;]
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template&lt;<i>execution-policy</i> Ep, random_access_iterator I, sized_sentinel_for&lt;I&gt; S,
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class Proj = identity, class T = projected_value_t&lt;I, Proj&gt;&gt;
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requires <ins>permutable&lt;I&gt; &amp;&amp;</ins>
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indirect_binary_predicate&lt;ranges::equal_to, projected&lt;I, Proj&gt;, const T*&gt;
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subrange&lt;I&gt;
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ranges::remove(Ep&amp; exec, I first, S last, const T&amp; value, Proj proj = {});
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template&lt;<i>execution-policy</i> Ep, <i>sized-random-access-range</i> R, class Proj = identity,
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class T = projected_value_t&lt;iterator_t&lt;R&gt;, Proj&gt;&gt;
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requires permutable&lt;iterator_t&lt;R&gt;&gt; &amp;&amp;
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indirect_binary_predicate&lt;ranges::equal_to,
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projected&lt;iterator_t&lt;R&gt;, Proj&gt;, const T*&gt;
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borrowed_subrange_t&lt;R&gt;
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ranges::remove(Ep&amp;&amp; exec, R&amp;&amp; r, const T&amp; value, Proj proj = {});
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[&hellip;]
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template&lt;<i>execution-policy</i> Ep, random_access_iterator I, sized_sentinel_for&lt;I&gt; S,
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class Proj = identity, indirect_unary_predicate&lt;projected&lt;I, Proj&gt;&gt; Pred&gt;
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<ins>requires permutable&lt;I&gt;</ins>
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subrange&lt;I&gt;
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ranges::remove_if(Ep&amp; exec, I first, S last, Pred pred, Proj proj = {});
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template&lt;<i>execution-policy</i> Ep, <i>sized-random-access-range</i> R, class Proj = identity,
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indirect_unary_predicate&lt;projected&lt;iterator_t&lt;R&gt;, Proj&gt;&gt; Pred&gt;
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requires permutable&lt;iterator_t&lt;R&gt;&gt;
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borrowed_subrange_t&lt;R&gt;
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ranges::remove_if(Ep&amp; exec, R&amp; r, Pred pred, Proj proj = {});
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</pre>
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<blockquote>
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<p>
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-1- Let <tt><i>E</i></tt> be [&hellip;]
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</p>
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</blockquote>
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</blockquote>
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</li>
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<li><p>Modify <sref ref="[alg.partitions]"/> as indicated:</p>
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<blockquote>
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<pre>
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[&hellip;]
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template&lt;execution-policy Ep, random_access_iterator I, sized_sentinel_for&lt;I&gt; S,
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class Proj = identity, indirect_unary_predicate&lt;projected&lt;I, Proj&gt;&gt; Pred&gt;
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<ins>requires permutable&lt;I&gt;</ins>
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subrange&lt;I&gt;
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ranges::partition(Ep&amp;&amp; exec, I first, S last, Pred pred, Proj proj = {});
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template&lt;<i>execution-policy</i> Ep, <i>sized-random-access-range</i> R, class Proj = identity,
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indirect_unary_predicate&lt;projected&lt;iterator_t&lt;R&gt;, Proj&gt;&gt; Pred&gt;
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requires permutable&lt;iterator_t&lt;R&gt;&gt;
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borrowed_subrange_t&lt;R&gt;
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ranges::partition(Ep&amp;&amp; exec, R&amp;&amp; r, Pred pred, Proj proj = {});
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</pre>
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<blockquote>
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<p>
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-1- Let `proj` be `identity{}` for the overloads with no parameter named `proj`.
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</p>
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</blockquote>
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</blockquote>
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</li>
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</ol>
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</resolution>
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</issue>

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