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<title>Issue 3296: Inconsistent default argument for basic_regex&lt;&gt;::assign</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++20">C++20</a> status.</em></p>
<h3 id="3296"><a href="lwg-defects.html#3296">3296</a>. Inconsistent default argument for <code>basic_regex&lt;&gt;::assign</code></h3>
<p><b>Section:</b> 28.6.7 <a href="https://wg21.link/re.regex">[re.regex]</a> <b>Status:</b> <a href="lwg-active.html#C++20">C++20</a>
 <b>Submitter:</b> Mark de Wever <b>Opened:</b> 2019-09-16 <b>Last modified:</b> 2021-02-25</p>
<p><b>Priority: </b>0
</p>
<p><b>View all other</b> <a href="lwg-index.html#re.regex">issues</a> in [re.regex].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#C++20">C++20</a> status.</p>
<p><b>Discussion:</b></p>
<p>
The declaration of the overload of <code>basic_regex&lt;&gt;::assign(const charT* p, size_t len, flag_type f)</code>
has an inconsistent default argument for the <code>flag_type f</code> parameter.
<p/>
28.6.7 <a href="https://wg21.link/re.regex">[re.regex]</a> p3:
</p>
<blockquote><pre>
basic_regex&amp; assign(const charT* p, size_t len, flag_type f);
</pre></blockquote>
<p>
28.6.7.3 <a href="https://wg21.link/re.regex.assign">[re.regex.assign]</a> before p12:
</p>
<blockquote><pre>
basic_regex&amp; assign(const charT* ptr, size_t len, flag_type f = regex_constants::ECMAScript);
</pre></blockquote>
<p>
Since all other overloads have a default argument in both 28.6.7 <a href="https://wg21.link/re.regex">[re.regex]</a> and
28.6.7.3 <a href="https://wg21.link/re.regex.assign">[re.regex.assign]</a> I propose to add a default argument for this overload
in the declaration in 28.6.7 <a href="https://wg21.link/re.regex">[re.regex]</a>.
<p/>
It should be pointed out that there exists implementation divergence due to the current
wording state: libc++ and libstdc++ do <em>not</em> implement the default argument.
The MS STL library <em>does</em> have the default argument.
</p>

<p><i>[2019-10-31 Issue Prioritization]</i></p>

<p>Status to Tentatively Ready and priority to 0 after six positive votes on the reflector.</p>


<p id="res-3296"><b>Proposed resolution:</b></p>
<p>This wording is relative to <a href="https://wg21.link/n4830">N4830</a>.</p>

<ol>
<li><p>Modify 28.6.7 <a href="https://wg21.link/re.regex">[re.regex]</a>, class template <code>basic_regex</code> synopsis, 
as indicated:</p>

<blockquote>
<pre>
[&hellip;]
<i>// 28.6.7.3 <a href="https://wg21.link/re.regex.assign">[re.regex.assign]</a>, assign</i>
[&hellip;]
basic_regex&amp; assign(const charT* ptr, flag_type f = regex_constants::ECMAScript);
basic_regex&amp; assign(const charT* p, size_t len, flag_type f <ins>= regex_constants::ECMAScript</ins>);
template&lt;class string_traits, class A&gt;
  basic_regex&amp; assign(const basic_string&lt;charT, string_traits, A&gt;&amp; s,
                      flag_type f = regex_constants::ECMAScript);
template&lt;class InputIterator&gt;
  basic_regex&amp; assign(InputIterator first, InputIterator last,
                      flag_type f = regex_constants::ECMAScript);
basic_regex&amp; assign(initializer_list&lt;charT&gt;,
                    flag_type = regex_constants::ECMAScript);
[&hellip;]
</pre>
</blockquote>
</li>
</ol>




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