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<title>Issue 1174: Type property predicates</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#Resolved">Resolved</a> status.</em></p>
<h3 id="1174"><a href="lwg-defects.html#1174">1174</a>. Type property predicates</h3>
<p><b>Section:</b> 21.3.6.4 <a href="https://wg21.link/meta.unary.prop">[meta.unary.prop]</a> <b>Status:</b> <a href="lwg-active.html#Resolved">Resolved</a>
 <b>Submitter:</b> Jason Merrill <b>Opened:</b> 2009-07-16 <b>Last modified:</b> 2016-01-28</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View other</b> <a href="lwg-index-open.html#meta.unary.prop">active issues</a> in [meta.unary.prop].</p>
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<p><b>Discussion:</b></p>
<p>
I've been implementing compiler support for <code>is_standard_layout</code>, and
noticed a few nits about 21.3.6.4 <a href="https://wg21.link/meta.unary.prop">[meta.unary.prop]</a>:
</p>

<ol>
<li>
There's no trait for "trivially copyable type", which is now the
property that lets you do bitwise copying of a type, and therefore seems
useful to be able to query.  <code>has_trivial_assign</code> &amp;&amp;
<code>has_trivial_copy_constructor</code> &amp;&amp; <code>has_trivial_destructor</code>
is similar, but
not identical, specifically with respect to const types.
</li>
<li>
<code>has_trivial_copy_constructor</code> and <code>has_trivial_assign</code> lack the "or an
array of such a class type" language that most other traits in that
section, including <code>has_nothrow_copy_constructor</code> and <code>has_nothrow_assign</code>,
have; this seems like an oversight.
</li>
</ol>

<p><i>[
See the thread starting with c++std-lib-24420 for further discussion.
]</i></p>


<p><i>[
Addressed in <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2947.html">N2947</a>.
]</i></p>


<p><i>[
2009-10 Santa Cruz:
]</i></p>


<blockquote><p>
<del>NAD Editorial</del><ins>Resolved</ins>.  Solved by
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2009/n2984.htm">N2984</a>.
</p></blockquote>



<p id="res-1174"><b>Proposed resolution:</b></p>
<p>
</p>





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