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<title>Issue 3925: Concept formattable's definition is incorrect</title>
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<p><em>This page is a snapshot from the LWG issues list, see the <a href="lwg-active.html">Library Active Issues List</a> for more information and the meaning of <a href="lwg-active.html#WP">WP</a> status.</em></p>
<h3 id="3925"><a href="lwg-defects.html#3925">3925</a>. Concept <code>formattable</code>'s definition is incorrect</h3>
<p><b>Section:</b> 28.5.6.3 <a href="https://wg21.link/format.formattable">[format.formattable]</a> <b>Status:</b> <a href="lwg-active.html#WP">WP</a>
 <b>Submitter:</b> Mark de Wever <b>Opened:</b> 2023-04-16 <b>Last modified:</b> 2023-11-22</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View other</b> <a href="lwg-index-open.html#format.formattable">active issues</a> in [format.formattable].</p>
<p><b>View all other</b> <a href="lwg-index.html#format.formattable">issues</a> in [format.formattable].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#WP">WP</a> status.</p>
<p><b>Discussion:</b></p>
<p>
LWG <a href="lwg-defects.html#3631" title="basic_format_arg(T&amp;&amp;) should use remove_cvref_t&lt;T&gt; throughout (Status: C++23)">3631</a><sup><a href="https://cplusplus.github.io/LWG/issue3631" title="Latest snapshot">(i)</a></sup> modified the <code>formattable</code> concept. The new wording 
contains a small issue: <code>basic_format_context</code> requires two template arguments, 
but only one is provided.
</p>

<p><i>[2023-05-24; Reflector poll]</i></p>

<p>
Set status to Tentatively Ready after ten votes in favour during reflector poll.
</p>

<p><i>[2023-06-17 Approved at June 2023 meeting in Varna. Status changed: Voting &rarr; WP.]</i></p>



<p id="res-3925"><b>Proposed resolution:</b></p>
<p>
This wording is relative to <a href="https://wg21.link/N4944" title=" Working Draft, Standard for Programming Language C++">N4944</a>.
</p>
<ol>
<li>
<p>Modify 28.5.6.3 <a href="https://wg21.link/format.formattable">[format.formattable]</a> as indicated:</p>

<blockquote>
<p>
-1- Let <code><i>fmt-iter-for</i>&lt;charT&gt;</code> be an unspecified type that models 
<code>output_iterator&lt;const charT&amp;&gt;</code> (24.3.4.10 <a href="https://wg21.link/iterator.concept.output">[iterator.concept.output]</a>).
</p>
<blockquote><pre>
[&hellip;]
template&lt;class T, class charT&gt;
  concept formattable =
    <i>formattable-with</i>&lt;remove_reference_t&lt;T&gt;, basic_format_context&lt;<i>fmt-iter-for</i>&lt;charT&gt;<ins>, charT</ins>&gt;&gt;;
</pre></blockquote>
</blockquote>
</li>

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