<html>
    <head>
      <base href="http://bugs.llvm.org/">
    </head>
    <body><table border="1" cellspacing="0" cellpadding="8">
        <tr>
          <th>Bug ID</th>
          <td><a class="bz_bug_link 
          bz_status_NEW "
   title="NEW - common_type<T> is not SFINAE-friendly"
   href="http://bugs.llvm.org/show_bug.cgi?id=32605">32605</a>
          </td>
        </tr>

        <tr>
          <th>Summary</th>
          <td>common_type<T> is not SFINAE-friendly
          </td>
        </tr>

        <tr>
          <th>Product</th>
          <td>libc++
          </td>
        </tr>

        <tr>
          <th>Version</th>
          <td>unspecified
          </td>
        </tr>

        <tr>
          <th>Hardware</th>
          <td>PC
          </td>
        </tr>

        <tr>
          <th>OS</th>
          <td>Windows NT
          </td>
        </tr>

        <tr>
          <th>Status</th>
          <td>NEW
          </td>
        </tr>

        <tr>
          <th>Severity</th>
          <td>enhancement
          </td>
        </tr>

        <tr>
          <th>Priority</th>
          <td>P
          </td>
        </tr>

        <tr>
          <th>Component</th>
          <td>All Bugs
          </td>
        </tr>

        <tr>
          <th>Assignee</th>
          <td>unassignedclangbugs@nondot.org
          </td>
        </tr>

        <tr>
          <th>Reporter</th>
          <td>rs2740@gmail.com
          </td>
        </tr>

        <tr>
          <th>CC</th>
          <td>llvm-bugs@lists.llvm.org, mclow.lists@gmail.com
          </td>
        </tr></table>
      <p>
        <div>
        <pre>The current implementation

template <class _Tp>
struct _LIBCPP_TEMPLATE_VIS common_type<_Tp>
{
    typedef typename common_type<_Tp, _Tp>::type type;
};

is incorrect, because common_type<_Tp, _Tp>::type need not exist, in which case
the current implementation will cause a hard error. This is the case for
abominable function types (although they currently fail due to a separate bug
in std::decay), and user-defined specializations may also fail to supply a
::type member. P0548 requires this case to be SFINAE-friendly.</pre>
        </div>
      </p>


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