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<title>Issue 232: &quot;depends&quot; poorly defined in 17.4.3.1</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#CD1">CD1</a> status.</em></p>
<h3 id="232"><a href="lwg-defects.html#232">232</a>. &quot;depends&quot; poorly defined in 17.4.3.1</h3>
<p><b>Section:</b> 16.4.5.3 <a href="https://wg21.link/reserved.names">[reserved.names]</a> <b>Status:</b> <a href="lwg-active.html#CD1">CD1</a>
 <b>Submitter:</b> Peter Dimov <b>Opened:</b> 2000-04-18 <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#reserved.names">issues</a> in [reserved.names].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#CD1">CD1</a> status.</p>
<p><b>Discussion:</b></p>
<p>17.4.3.1/1 uses the term &quot;depends&quot; to limit the set of allowed
specializations of standard templates to those that &quot;depend on a
user-defined name of external linkage.&quot;</p>
<p>This term, however, is not adequately defined, making it possible to
construct a specialization that is, I believe, technically legal according to
17.4.3.1/1, but that specializes a standard template for a built-in type such as
'int'.</p>
<p>The following code demonstrates the problem:</p>
<blockquote>
  <pre>#include &lt;algorithm&gt;</pre>
  <pre>template&lt;class T&gt; struct X
{
 typedef T type;
};</pre>
  <pre>namespace std
{
 template&lt;&gt; void swap(::X&lt;int&gt;::type&amp; i, ::X&lt;int&gt;::type&amp; j);
}</pre>
</blockquote>


<p id="res-232"><b>Proposed resolution:</b></p>
<p>Change &quot;user-defined name&quot; to &quot;user-defined
type&quot;.</p>


<p><b>Rationale:</b></p>
<p>This terminology is used in section 2.5.2 and 4.1.1 of <i>The C++
Programming Language</i>.  It disallows the example in the issue,
since the underlying type itself is not user-defined.  The only
possible problem I can see is for non-type templates, but there's no
possible way for a user to come up with a specialization for bitset,
for example, that might not have already been specialized by the
implementor?</p>

<p><i>[Toronto: this may be related to issue <a href="lwg-defects.html#120" title="Can an implementor add specializations? (Status: CD1)">120</a><sup><a href="https://cplusplus.github.io/LWG/issue120" title="Latest snapshot">(i)</a></sup>.]</i></p>


<p><i>[post-Toronto: Judy provided the above proposed resolution and
rationale.]</i></p>






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