title: How do I get index of elements in parameter pack
body: <p>How do I get the following to put the index of the parameter pack element in the tuple?</p>
  
  <pre><code>template&lt; typename... Ts &gt;
  class ClassA {
  public:
      ClassA( Ts... ts ) : tup( make_tuple( ts, 0 )... ) {}
      // I would like it to expand to this.
      // ClassA( T0 ts0, T1 ts1 ) : tup( make_tuple( ts0, 0 ), make_tuple(ts1, 1) ) {}
      tuple&lt;tuple&lt;Ts, size_t&gt;...&gt; tup;
  };
  
  void main() {
      vector&lt;int&gt; a ={ 2, 4, 5 };
      list&lt;double&gt; b ={ 1.1, 2.2, 3.3 };
      ClassA&lt;vector&lt;int&gt;, list&lt;double&gt;, vector&lt;int&gt;, list&lt;double&gt;&gt; mm( a, b, a, b );
  }
  </code></pre>
  
  <p>Thanks.</p>