New issue from Hewill Kang: "enumerate_view::iterator and cartesian_product_view::iterator should not always provide iterator_category"

Author: Dani-Hub

xml/issue4116.xml

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+<?xml version='1.0' encoding='utf-8' standalone='no'?>
+<!DOCTYPE issue SYSTEM "lwg-issue.dtd">
+
+<issue num="4116" status="New">
+<title><tt>enumerate_view::<i>iterator</i></tt> and <tt>cartesian_product_view::<i>iterator</i></tt> should not
+    always provide <tt>iterator_category</tt></title>
+<section><sref ref="[range.enumerate.iterator]"/><sref ref="[range.cartesian.iterator]"/></section>
+<submitter>Hewill Kang</submitter>
+<date>07 Jul 2024</date>
+<priority>99</priority>
+
+<discussion>
+<p>
+These two iterators do not support <tt>*r++</tt> for non-forward iterators,
+so we should not provide <tt>iterator_category</tt> as they are not C++17 iterators.
+</p>
+</discussion>
+
+<resolution>
+<p>
+This wording is relative to <paper num="N4981"/>.
+</p>
+
+<ol>
+<li><p>Modify <sref ref="[range.enumerate.iterator]"/> as indicated:</p>
+
+<blockquote><pre>
+namespace std::ranges {
+  template&lt;view V&gt;
+    requires <i>range-with-movable-references</i>&lt;V&gt;
+  template&lt;bool Const&gt;
+  class enumerate_view&lt;V&gt;::<i>iterator</i> {
+    using <i>Base</i> = <i>maybe-const</i>&lt;Const, V&gt;;                         // <i>exposition only</i>
+
+  public:
+    using iterator_category = input_iterator_tag;      <ins>// present only if <i>Base</i>
+                                                       // models forward_range</ins>
+    using iterator_concept = <i>see below</i>;
+    [&hellip;]
+  };
+}
+</pre></blockquote>
+
+</li>
+
+<li><p>Modify <sref ref="[range.cartesian.iterator]"/> as indicated:</p>
+
+<blockquote>
+<pre>
+namespace std::ranges {
+  template&lt;input_range First, forward_range... Vs&gt;
+    requires (view&lt;First&gt; &amp;&amp; ... &amp;&amp; view&lt;Vs&gt;)
+  template&lt;bool Const&gt;
+  class cartesian_product_view&lt;First, Vs...&gt;::<i>iterator</i> {
+  public:
+    using iterator_category = input_iterator_tag;      <ins>// present only if <i><i>maybe-const</i>&lt;Const, First&gt;</i>
+                                                       // models forward_range</ins>
+    using iterator_concept  = see below;
+    [&hellip;]
+  };
+}
+</pre>
+</blockquote>
+
+</li>
+</ol>
+</resolution>
+
+</issue>