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<title>Issue 3654: basic_format_context::arg(size_t) should be noexcept</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#C++23">C++23</a> status.</em></p>
<h3 id="3654"><a href="lwg-defects.html#3654">3654</a>. <code>basic_format_context::arg(size_t)</code> should be <code>noexcept</code></h3>
<p><b>Section:</b> 28.5.6.7 <a href="https://wg21.link/format.context">[format.context]</a> <b>Status:</b> <a href="lwg-active.html#C++23">C++23</a>
 <b>Submitter:</b> Hewill Kang <b>Opened:</b> 2021-12-26 <b>Last modified:</b> 2023-11-22</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View all other</b> <a href="lwg-index.html#format.context">issues</a> in [format.context].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#C++23">C++23</a> status.</p>
<p><b>Discussion:</b></p>
<p>
<code>basic_format_context::arg(size_t)</code> simply returns <code>args_.get(id)</code> to get the elements of 
<code>args_</code>, where the type of <code>args_</code> is <code>basic_format_args&lt;basic_format_context&gt;</code>. 
Since <code>basic_format_args</code>'s <code>get(size_t)</code> is <code>noexcept</code>, this function can also be 
<code>noexcept</code>.
</p>

<p><i>[2022-01-30; Reflector poll]</i></p>

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

<p><i>[2022-02-10 Approved at February 2022 virtual plenary. Status changed: Tentatively Ready &rarr; WP.]</i></p>



<p id="res-3654"><b>Proposed resolution:</b></p>
<p>
This wording is relative to <a href="https://wg21.link/N4901" title=" Working Draft, Standard for Programming Language C++">N4901</a>. 
</p>

<ol>
<li><p>Modify 28.5.6.7 <a href="https://wg21.link/format.context">[format.context]</a> as indicated:</p>

<blockquote>
<blockquote>
<pre>
namespace std {
  template&lt;class Out, class charT&gt;
  class basic_format_context {
    basic_format_args&lt;basic_format_context&gt; args_; <i>// exposition only</i>
    Out out_; <i>// exposition only</i>
  public:
    using iterator = Out;
    using char_type = charT;
    template&lt;class T&gt; using formatter_type = formatter&lt;T, charT&gt;;
    
    basic_format_arg&lt;basic_format_context&gt; arg(size_t id) const <ins>noexcept</ins>;
    std::locale locale();

    iterator out();
    void advance_to(iterator it);
  };
}
</pre>
</blockquote>
<p>
[&hellip;]
</p>
<pre>
basic_format_arg&lt;basic_format_context&gt; arg(size_t id) const <ins>noexcept</ins>;
</pre>
<blockquote>
<p>
-5- <i>Returns:</i> <code>args_.get(id)</code>.
</p>
</blockquote>
</blockquote>
</li>
</ol>





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