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<title>Issue 2371: [fund.ts] No template aliases defined for new type traits</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#TS">TS</a> status.</em></p>
<h3 id="2371"><a href="lwg-defects.html#2371">2371</a>. [fund.ts] No template aliases defined for new type traits</h3>
<p><b>Section:</b> 3.3.1 <a href="https://cplusplus.github.io/fundamentals-ts/v1.html#meta.type.synop">[fund.ts::meta.type.synop]</a> <b>Status:</b> <a href="lwg-active.html#TS">TS</a>
 <b>Submitter:</b> Joe Gottman <b>Opened:</b> 2014-03-07 <b>Last modified:</b> 2017-07-30</p>
<p><b>Priority: </b>0
</p>
<p><b>View all issues with</b> <a href="lwg-status.html#TS">TS</a> status.</p>
<p><b>Discussion:</b></p>
<p><b>Addresses: fund.ts</b></p>

<p>
The library fundamentals specification defines two new type trait template classes: <code>invocation_type</code> and <code>raw_invocation_type</code>.  
But it does not define the corresponding template aliases. Note that both of these classes define a member typedef <code>type</code> and no 
other public members, so according to the argument in <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n3887.pdf">N3887</a> 
the template aliases should be defined.
</p>

<p><i>[2013-06-21 Rapperswil]</i></p>

<p>
Accept for Library Fundamentals TS Working Paper
</p>


<p id="res-2371"><b>Proposed resolution:</b></p>
<p>This wording is relative to <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n3908.html">N3908</a>.</p>

<ol>
<li><p>Add the following to section 3.3.1[meta.type.synop] of the 
<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2014/n3908.html#meta">Library Fundamentals specification</a>
as indicated:
</p>

<blockquote><pre>
namespace std {
namespace experimental {
inline namespace fundamentals_v1 {
  [&hellip;]
  <i>// 3.3.2, Other type transformations</i>
  template &lt;class&gt; class invocation_type; <i>// not defined</i>
  template &lt;class F, class... ArgTypes&gt; class invocation_type&lt;F(ArgTypes...)&gt;;
  template &lt;class&gt; class raw_invocation_type; <i>// not defined</i>
  template &lt;class F, class... ArgTypes&gt; class raw_invocation_type&lt;F(ArgTypes...)&gt;;
  
  <ins>template &lt;class T&gt; 
    using invocation_type_t = typename invocation_type&lt;T&gt;::type;
  template &lt;class T&gt; 
    using raw_invocation_type_t = typename raw_invocation_type&lt;T&gt;::type;</ins>
  
} <i>// namespace fundamentals_v1</i>
} <i>// namespace experimental</i>
} <i>// namespace std</i>
</pre></blockquote>
</li>

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