title: Get value without knowing key in one-pair-associative-array
body: <p>There is an associative array with <strong>only one</strong> pair <code>key=&gt;value</code>. </p>
  
  <p>I don't know it's key, but I need to get it's value: </p>
  
  <pre><code>$array = array('???' =&gt; 'value');
  $value = // ??
  </code></pre>
  
  <p><code>$array[0]</code> doesn't work.</p>
  
  <p>How can I get it's value?  </p>