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<title>Issue 2330: regex("meow", regex::icase) is technically forbidden but should be permitted</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++14">C++14</a> status.</em></p>
<h3 id="2330"><a href="lwg-defects.html#2330">2330</a>. <code>regex("meow", regex::icase)</code> is technically forbidden but should be permitted</h3>
<p><b>Section:</b> 28.6.4.2 <a href="https://wg21.link/re.synopt">[re.synopt]</a> <b>Status:</b> <a href="lwg-active.html#C++14">C++14</a>
 <b>Submitter:</b> Stephan T. Lavavej <b>Opened:</b> 2013-09-21 <b>Last modified:</b> 2017-07-05</p>
<p><b>Priority: </b>0
</p>
<p><b>View all other</b> <a href="lwg-index.html#re.synopt">issues</a> in [re.synopt].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#C++14">C++14</a> status.</p>
<p><b>Discussion:</b></p>
<p>
28.6.4.2 <a href="https://wg21.link/re.synopt">[re.synopt]</a>/1 says "A valid value of type <code>syntax_option_type</code> shall have exactly one of the elements 
<code>ECMAScript</code>, <code>basic</code>, <code>extended</code>, <code>awk</code>, <code>grep</code>, <code>egrep</code>, set." 
<p/>
This "exactly one" wording technically forbids passing <code>icase</code> by itself! Users should not be required to pass 
<code>regex::ECMAScript | regex::icase</code>. (Note that the cost of an additional check for no grammar being explicitly requested 
is completely irrelevant, as regex construction is so much more expensive.)
</p>

<p><i>[Issaquah 2014-02-11: Move to Immediate]</i></p>




<p id="res-2330"><b>Proposed resolution:</b></p>
<p>This wording is relative to N3691.</p>

<ol>
<li><p>Edit 28.6.4.2 <a href="https://wg21.link/re.synopt">[re.synopt]</a> as indicated:</p>

<blockquote><p>
-1- The type <code>syntax_option_type</code> is an implementation-defined bitmask type (17.5.2.1.3). Setting its elements
has the effects listed in table 138. A valid value of type <code>syntax_option_type</code> shall have <del>exactly</del><ins>at most</ins> 
one of the <ins>grammar</ins> elements <code>ECMAScript</code>, <code>basic</code>, <code>extended</code>, <code>awk</code>, <code>grep</code>, 
<code>egrep</code>, set. <ins> If no grammar element is set, the default grammar is <code>ECMAScript</code>.</ins>
</p></blockquote>
</li>
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