title: Going from hana::tuple_t to hana::tuple
body: <p>I have a <code>hana::tuple_t&lt;int, char, double, float&gt;</code>, and I want to use this to create a <code>hana::tuple&lt;int, char, double, float&gt;</code>. </p>
  
  <p>I thought that using <code>hana::to&lt;hana::tuple_tag&gt;</code> would transform the <code>hana::tuple_t&lt;int, char, double, float&gt;</code> into a <code>hana::tuple&lt;int, char, double, float&gt;</code>; but that is not the case since the following always fails:</p>
  
  <pre><code>auto oType = hana::tuple_t&lt;int, char, double, float&gt;;
  
  BOOST_HANA_CONSTANT_ASSERT(
      hana::to&lt;hana::tuple_tag&gt;(oType)
      ==
      hana::make_tuple(1, 'C', 1.0, 1.0f)
  );
  </code></pre>
  
  <p>I've also tried using <code>hana::transform</code>, but with no luck (although I suspect I'm doing it wrong):</p>
  
  <pre><code>auto vecs = hana::transform(typeList, [](auto t) {
      return typename decltype(t)::type{};
  });
  </code></pre>
  
  <p>So, how do I go about turning a hana::tuple_t into a hana::tuple? </p>