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    <head>
      <base href="http://llvm.org/bugs/" />
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    <body><table border="1" cellspacing="0" cellpadding="8">
        <tr>
          <th>Bug ID</th>
          <td><a class="bz_bug_link 
          bz_status_NEW "
   title="NEW --- - Variadic pack at the beginning of function parameters not seen as a non-deduced context"
   href="http://llvm.org/bugs/show_bug.cgi?id=15799">15799</a>
          </td>
        </tr>

        <tr>
          <th>Summary</th>
          <td>Variadic pack at the beginning of function parameters not seen as a non-deduced context
          </td>
        </tr>

        <tr>
          <th>Product</th>
          <td>clang
          </td>
        </tr>

        <tr>
          <th>Version</th>
          <td>trunk
          </td>
        </tr>

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

        <tr>
          <th>OS</th>
          <td>Linux
          </td>
        </tr>

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

        <tr>
          <th>Severity</th>
          <td>normal
          </td>
        </tr>

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

        <tr>
          <th>Component</th>
          <td>C++11
          </td>
        </tr>

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

        <tr>
          <th>Reporter</th>
          <td>hivemaster@hotmail.de
          </td>
        </tr>

        <tr>
          <th>CC</th>
          <td>dgregor@apple.com, llvmbugs@cs.uiuc.edu
          </td>
        </tr>

        <tr>
          <th>Classification</th>
          <td>Unclassified
          </td>
        </tr></table>
      <p>
        <div>
        <pre>The following simple snippet fails to compile:

template<typename T> struct any{ template<typename U> any(U){} };

template<typename... Ts, typename T>
T back(any<Ts>..., T);

int main(){
    using _ = decltype(back<int>(true, 42));
}

With:

main.cpp:7:24: error: no matching function for call to 'back'
    using _ = decltype(back<int>(true, 42));
                       ^~~~~~~~~
main.cpp:4:3: note: candidate template ignored: couldn't infer template
argument 'T'
T back(any<Ts>..., T);

May be related to <a class="bz_bug_link 
          bz_status_NEW "
   title="NEW --- - Pack expansion that was already expanded treated as a non-deduced context."
   href="show_bug.cgi?id=9020">http://llvm.org/bugs/show_bug.cgi?id=9020</a></pre>
        </div>
      </p>
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