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<title>Issue 138: Class ctype_byname&lt;char&gt; redundant and misleading</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#NAD">NAD</a> status.</em></p>
<h3 id="138"><a href="lwg-closed.html#138">138</a>. Class <code>ctype_byname&lt;char&gt;</code> redundant and misleading</h3>
<p><b>Section:</b> 28.3.4.2.5 <a href="https://wg21.link/locale.codecvt">[locale.codecvt]</a> <b>Status:</b> <a href="lwg-active.html#NAD">NAD</a>
 <b>Submitter:</b> Angelika Langer <b>Opened:</b> 1999-03-18 <b>Last modified:</b> 2016-01-28</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View all other</b> <a href="lwg-index.html#locale.codecvt">issues</a> in [locale.codecvt].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#NAD">NAD</a> status.</p>
<p><b>Discussion:</b></p>
<p>Section 28.3.4.2.5 <a href="https://wg21.link/locale.codecvt">[locale.codecvt]</a> specifies that
<code>ctype_byname&lt;char&gt;</code> must be a specialization of the <code>ctype_byname</code>
template.</p>

<p>It is common practice in the standard that specializations of class templates are only
mentioned where the interface of the specialization deviates from the interface of the
template that it is a specialization of. Otherwise, the fact whether or not a required
instantiation is an actual instantiation or a specialization is left open as an
implementation detail. </p>

<p>Clause 22.2.1.4 deviates from that practice and for that reason is misleading. The
fact, that <code>ctype_byname&lt;char&gt;</code> is specified as a specialization suggests that there
must be something &quot;special&quot; about it, but it has the exact same interface as the
<code>ctype_byname</code> template. Clause 22.2.1.4 does not have any explanatory value, is at best
redundant, at worst misleading - unless I am missing anything. </p>

<p>Naturally, an implementation will most likely implement <code>ctype_byname&lt;char&gt;</code> as a
specialization, because the base class <code>ctype&lt;char&gt;</code> is a specialization with an
interface different from the <code>ctype</code> template, but that's an implementation detail and need
not be mentioned in the standard. </p>

<p><i>[
Summit:
]</i></p>


<blockquote><p>
Reopened by Alisdair.
</p></blockquote>

<p><i>[
2009-07 Frankfurt
]</i></p>


<blockquote><p>
Moved to NAD.
</p></blockquote>



<p><b>Rationale:</b></p>
<p> The standard as written is mildly misleading, but the correct fix
is to deal with the underlying problem in the <code>ctype_byname</code> base class,
not in the specialization. See issue <a href="lwg-defects.html#228" title="Incorrect specification of &quot;..._byname&quot; facets (Status: CD1)">228</a><sup><a href="https://cplusplus.github.io/LWG/issue228" title="Latest snapshot">(i)</a></sup>.</p>




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