title: PHP: implode() Invalid arguments passed
body: <p>I am using Codeigniter and its validation rules - a custom callback validation. Anyway, this seems not to be CI related I think.</p>
  
  <p>I've got this function to return a string …</p>
  
  <pre><code>function array_implode($a)
  {
    return implode(',', $a);
  }
  </code></pre>
  
  <p>… but I always get a message implode(): Invalid arguments passed</p>
  
  <p>But <code>var_dump()</code> shows me this:</p>
  
  <pre><code>array(2) {
    [0]=&gt; string(10) "First item"
    [1]=&gt; string(11) "Second item"
  }
  </code></pre>
  
  <p>What is wrong? </p>