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<title>Issue 3515: &sect;[stacktrace.basic.nonmem]: operator&lt;&lt; should be less templatized</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="3515"><a href="lwg-defects.html#3515">3515</a>. &sect;[stacktrace.basic.nonmem]: <code>operator&lt;&lt;</code> should be less templatized</h3>
<p><b>Section:</b> 19.6.2 <a href="https://wg21.link/stacktrace.syn">[stacktrace.syn]</a>, 19.6.4.6 <a href="https://wg21.link/stacktrace.basic.nonmem">[stacktrace.basic.nonmem]</a> <b>Status:</b> <a href="lwg-active.html#C++23">C++23</a>
 <b>Submitter:</b> Jiang An <b>Opened:</b> 2021-01-25 <b>Last modified:</b> 2023-11-22</p>
<p><b>Priority: </b>2
</p>
<p><b>View all other</b> <a href="lwg-index.html#stacktrace.syn">issues</a> in [stacktrace.syn].</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>
According to 27.4.4.4 <a href="https://wg21.link/string.io">[string.io]</a>, the <code>operator&lt;&lt;</code> overloads in 
19.6.4.6 <a href="https://wg21.link/stacktrace.basic.nonmem">[stacktrace.basic.nonmem]</a> are well-formed only if the template parameters 
<code>charT</code> and <code>traits</code> are <code>char</code> and <code>std::char_traits&lt;char&gt;</code> 
(that of <code>std::string</code>) respectively, because it is required in <i>Effects:</i> that 
these overloads behave as-if insert a <code>std::string</code>.
<p/>
I think the declarations of these overloads should be changed to:
</p>
<blockquote><pre>
ostream&amp; operator&lt;&lt;(ostream&amp; os, const stacktrace_entry&amp; f); 

template&lt;class Allocator&gt;
ostream&amp; operator&lt;&lt;(ostream&amp; os, const basic_stacktrace&lt;Allocator&gt;&amp; st);
</pre></blockquote>

<p><i>[2021-03-12; Reflector poll]</i></p>

<p>
Set priority to 2 and status to LEWG following reflector poll.
</p>

<p><i>[2022-11-07; Kona]</i></p>

<p>Move to Immediate.</p>

<p><i>[2022-11-12 Approved at November 2022 meeting in Kona. Status changed: Immediate &rarr; WP.]</i></p>



<p id="res-3515"><b>Proposed resolution:</b></p>
<p>
This wording is relative to <a href="https://wg21.link/n4878">N4878</a>. 
</p>

<ol>
<li><p>Modify 19.6.2 <a href="https://wg21.link/stacktrace.syn">[stacktrace.syn]</a>, header <code>&lt;stacktrace&gt;</code> synopsis, as indicated:</p>

<blockquote><pre>
namespace std {
  <i>// 19.6.3 <a href="https://wg21.link/stacktrace.entry">[stacktrace.entry]</a>, class stacktrace_entry</i>
  class stacktrace_entry;
  
  <i>// 19.6.4 <a href="https://wg21.link/stacktrace.basic">[stacktrace.basic]</a>, class template basic_stacktrace</i>
  template&lt;class Allocator&gt;
  class basic_stacktrace;
  
  [&hellip;]
  
  <i>// 19.6.4.6 <a href="https://wg21.link/stacktrace.basic.nonmem">[stacktrace.basic.nonmem]</a>, non-member functions</i>
  [&hellip;]
  
  string to_string(const stacktrace_entry&amp; f);
  
  template&lt;class Allocator&gt;
    string to_string(const basic_stacktrace&lt;Allocator&gt;&amp; st);
  
  <del>template&lt;class charT, class traits&gt;
    basic_</del>ostream<del>&lt;charT, traits&gt;</del>&amp;
      operator&lt;&lt;(<del>basic_</del>ostream<del>&lt;charT, traits&gt;</del>&amp; os, const stacktrace_entry&amp; f);
    
  template&lt;<del>class charT, class traits, </del>class Allocator&gt;
    <del>basic_</del>ostream<del>&lt;charT, traits&gt;</del>&amp;
      operator&lt;&lt;(<del>basic_</del>ostream<del>&lt;charT, traits&gt;</del>&amp; os, const basic_stacktrace&lt;Allocator&gt;&amp; st);
  
  [&hellip;]
}
</pre></blockquote>
</li>

<li><p>Modify 19.6.4.6 <a href="https://wg21.link/stacktrace.basic.nonmem">[stacktrace.basic.nonmem]</a> as indicated:</p>

<blockquote>
<pre>
<del>template&lt;class charT, class traits&gt;
basic_</del>ostream<del>&lt;charT, traits&gt;</del>&amp;
  operator&lt;&lt;(<del>basic_</del>ostream<del>&lt;charT, traits&gt;</del>&amp; os, const stacktrace_entry&amp; f);
</pre>
<blockquote>
<p>
-4- <i>Effects:</i> Equivalent to: <code>return os &lt;&lt; to_string(f);</code>
</p>
</blockquote>
<pre>
template&lt;<del>class charT, class traits, </del>class Allocator&gt;
<del>basic_</del>ostream<del>&lt;charT, traits&gt;</del>&amp;
  operator&lt;&lt;(<del>basic_</del>ostream<del>&lt;charT, traits&gt;</del>&amp; os, const basic_stacktrace&lt;Allocator&gt;&amp; st);
</pre>
<blockquote>
<p>
-5- <i>Effects:</i> Equivalent to: <code>return os &lt;&lt; to_string(st);</code>
</p>
</blockquote>
</blockquote>
</li>
</ol>





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