 array are initially
   physically equal to <code class="code">x</code> (in the sense of the <code class="code">==</code> predicate).
   Consequently, if <code class="code">x</code> is mutable, it is shared among all elements
   of the array, and modifying <code class="code">x</code> through one of the array entries
   will modify all other entries at the same time.
<p>

   Raise <code class="code"><span class="constructor">Invalid_argument</span></code> if <code class="code">n &lt; 0</code> or <code class=