title: Multiplication of Template Arguments
body: <p>I have the following problem:</p>
  
  <pre><code>template&lt; size_t... N_i &gt;
  class A
  {
    // ...
    std::array&lt; float, /* product of the unpacked elements of N_i */ &gt; arr;
  };
  </code></pre>
  
  <p>As you can see above, I try to declare an <code>std::array</code> named <code>arr</code> as a member of a class <code>A</code>. Here, I want <code>arr</code> to have the size <em>product of the unpacked elements of <code>N_i</code></em>, e.g., in case of <code>A&lt;2,3,4&gt;</code>, "arr" should have the size <code>2*3*4=24</code>.<br>
  Does anyone know how this can be implemented?</p>