pes.
They are constructed with a call to the <code>tie</code> function template (cf. <code>make_tuple</code>):

<pre><code>int i; char c; double d; 
  ...
tie(i, c, a);
</code></pre>

<p>
The above <code>tie</code> function creates a tuple of type <code>tuple&lt;int&amp;, char&amp;, double&amp;&gt;</code>. 
The same result could be achieved with the call <code>make_tuple(ref(i), ref(c), ref(a))</code>.
</p>

<p>
A tuple that contains non-const references as elements can be used to 'unpack' another tuple int