New issue from Tomasz: "enable_nonlocking_formatter_optimization for pair and tuple needs remove_cvref_t"

Author: Dani-Hub

xml/issue4399.xml

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+<?xml version='1.0' encoding='utf-8' standalone='no'?>
+<!DOCTYPE issue SYSTEM "lwg-issue.dtd">
+
+<issue num="4399" status="New">
+<title>`enable_nonlocking_formatter_optimization` for `pair` and `tuple` needs `remove_cvref_t`</title>
+<section><sref ref="[format.tuple]"/></section>
+<submitter>Tomasz Kamiński</submitter>
+<date>02 Oct 2025</date>
+<priority>99</priority>
+
+<discussion>
+<p>
+The `enable_nonlocking_formatter_optimization` variable template is specialized only for <i>cv</i>-unqualified 
+types. However, the specialization for `pair` and `tuple` does not remove the references and 
+<i>cv</i>-qualifiers from the elements:
+</p>
+<blockquote><pre>
+template&lt;class... Ts&gt; 
+  constexpr bool enable_nonlocking_formatter_optimization&lt;<i>pair-or-tuple</i>&lt;Ts...&gt;&gt; = 
+    (enable_nonlocking_formatter_optimization&lt;Ts&gt; &amp;&amp; ...);
+</pre></blockquote>
+<p>
+As consequence <tt>pair&lt;const std::string, int&gt;</tt> or 
+<tt>pair&lt;const std::string&amp;, int&amp;&gt;</tt> (`map` and `flat_map` reference types) 
+will not use unbuffered prints.
+</p>
+</discussion>
+
+<resolution>
+<p>
+This wording is relative to <paper num="N5014"/>.
+</p>
+
+<ol>
+
+<li><p>Modify <sref ref="[format.tuple]"/> as indicated:</p>
+
+<blockquote>
+<p>
+-1- For each of `pair` and `tuple`, the library provides the following formatter specialization 
+where <tt><i>pair-or-tuple</i></tt> is the name of the template:
+</p>
+<blockquote>
+<pre>
+namespace std {
+  [&hellip;]
+  
+  template&lt;class... Ts&gt; 
+    constexpr bool enable_nonlocking_formatter_optimization&lt;<i>pair-or-tuple</i>&lt;Ts...&gt;&gt; = 
+      (enable_nonlocking_formatter_optimization&lt;<ins>remove_cvref_t&lt;</ins>Ts<ins>&gt;</ins>&gt; &amp;&amp; ...);
+}
+</pre>
+</blockquote>
+</blockquote>
+</li>
+</ol>
+
+</resolution>
+
+</issue>