title: Iterate through map with tuple
body: <p>I am trying to iterate through a map, that has a tuple. The below fails </p>
  
  <pre><code>std::map&lt;int, std::tuple&lt;int,       double, double, double&gt;&gt; database;
  
  for (auto d : database){  
          if (std::get&lt;3&gt;(d) &gt; temp){
              json tmp;
              tmp = { 
              { "result", "ok" },
              { "id", id },
              { "timestamp", std::get&lt;0&gt;(d) },
              { "x", std::get&lt;1&gt;(d) },
              { "y", std::get&lt;2&gt;(d) },
              { "temperature", std::get&lt;3&gt;(d) } 
              };
              result+=tmp;
          }
          id++;
  }
  </code></pre>
  
  <p>The error message is massive, this is the first part</p>
  
  <pre><code>temperature_server.cc:83:30: error: no matching function for call to 'get(std::pair&lt;const int, std::tuple&lt;int, double, double, double&gt; &gt;&amp;)'
           if (std::get&lt;3&gt;(d) &gt; temp){
  </code></pre>