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<title>Issue 2599: Library incomplete type permission phrase is unclear</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#New">New</a> status.</em></p>
<h3 id="2599"><a href="lwg-active.html#2599">2599</a>. Library incomplete type permission phrase is unclear</h3>
<p><b>Section:</b> 22.2.6 <a href="https://wg21.link/declval">[declval]</a>, 20.3.1 <a href="https://wg21.link/unique.ptr">[unique.ptr]</a>, 20.3.1.2.1 <a href="https://wg21.link/unique.ptr.dltr.general">[unique.ptr.dltr.general]</a>, 20.3.2.2 <a href="https://wg21.link/util.smartptr.shared">[util.smartptr.shared]</a>, 20.3.2.3 <a href="https://wg21.link/util.smartptr.weak">[util.smartptr.weak]</a>, 20.3.2.7 <a href="https://wg21.link/util.smartptr.enab">[util.smartptr.enab]</a> <b>Status:</b> <a href="lwg-active.html#New">New</a>
 <b>Submitter:</b> Zhihao Yuan <b>Opened:</b> 2016-03-08 <b>Last modified:</b> 2016-04-16</p>
<p><b>Priority: </b>3
</p>
<p><b>View other</b> <a href="lwg-index-open.html#declval">active issues</a> in [declval].</p>
<p><b>View all other</b> <a href="lwg-index.html#declval">issues</a> in [declval].</p>
<p><b>View all issues with</b> <a href="lwg-status.html#New">New</a> status.</p>
<p><b>Discussion:</b></p>
<p>
Currently the phrase to grant this permission is:
</p>
<blockquote><p>
The template parameter <code>T</code> of <code><i>LibraryTemplate</i></code> may be an incomplete type.
</p></blockquote>
<p>
Two problems:
</p>
<ol>
<li><p>The timing is unclear.  We always allow specializations like <code><i>LibraryTemplate</i>&lt;Incomp&gt;* p;</code></p></li>
<li><p>To the users of a template, the correct terminology should be "argument" rather than "parameter".</p></li>
</ol>
<p>
Suggested resolution:
</p>
<blockquote><p>
In an instantiation of <code><i>LibraryTemplate</i></code>, an incomplete type
may be used as the template argument for the template parameter <code>T</code>.
</p></blockquote>
<p>
as shown <a href="https://github.com/cplusplus/draft/pull/304/files">here</a>.
<p/>
Or, to copy <a href=" http://www.open-std.org/JTC1/SC22/WG21/docs/papers/2015/n4510.html">N4510's wording</a>:
</p>
<blockquote><p>
An incomplete type <code>T</code> may be used when instantiating <code><i>LibraryTemplate</i></code>.
</p></blockquote>


<p id="res-2599"><b>Proposed resolution:</b></p>





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