preg_replace_callback requires argument 2 to be a valid callback... Stuck!
<pre><code>public function make_url_clickable_cb($matches) {
$ret = '';
$url = $matches[2];

if ( empty($url) )
    return $matches[0];
// removed trailing [.,;:] from URL
if ( in_array(substr($url, -1), array('.', ',', ';', ':')) === true ) {
    $ret = substr($url, -1);
    $url = substr($url, 0, strlen($url)-1);
}
return $matches[1] . "&lt;a href=\"$url\" rel=\"nofollow\"&gt;" . $this-&gt;truncate($url, 35, '...'). "&lt;/a&gt;" . $ret;
}

public function make_web_ftp_clickable_cb($matches) {
    $ret = '';
    $dest = $matches[2];
    $dest = 'http://' . $dest;

    if ( empty($dest) )
        return $matches[0];
    // removed trailing [,;:] from URL
    if ( in_array(substr($dest, -1), array('.', ',', ';', ':')) === true ) {
        $ret = substr($dest, -1);
        $dest = substr($dest, 0, strlen($dest)-1);
    }
    return $matches[1] . "&lt;a href=\"$dest\" rel=\"nofollow\"&gt;$dest&lt;/a&gt;" . $ret;
}

public function make_email_clickable_cb($matches) {
    $email = $matches[2] . '@' . $matches[3];
    return $matches[1] . "&lt;a href=\"mailto:$email\"&gt;$email&lt;/a&gt;";
}
public function make_clickable($ret) {
    $ret = ' ' . $ret;
    // in testing, using arrays here was found to be faster
    $ret = preg_replace_callback('#([\s&gt;])([\w]+?://[\w\\x80-\\xff\#$%&amp;~/.\-;:=,?@\[\]+]*)#is', 'Main::make_url_clickable_cb', $ret);
    $ret = preg_replace_callback('#([\s&gt;])((www|ftp)\.[\w\\x80-\\xff\#$%&amp;~/.\-;:=,?@\[\]+]*)#is', 'Main::make_web_ftp_clickable_cb', $ret);
    $ret = preg_replace_callback('#([\s&gt;])([.0-9a-z_+-]+)@(([0-9a-z-]+\.)+[0-9a-z]{2,})#i', 'Main::make_email_clickable_cb', $ret);

    // this one is not in an array because we need it to run last, for cleanup of accidental links within links
    $ret = preg_replace("#(&lt;a( [^&gt;]+?&gt;|&gt;))&lt;a [^&gt;]+?&gt;([^&gt;]+?)&lt;/a&gt;&lt;/a&gt;#i", "$1$3&lt;/a&gt;", $ret);
    $ret = trim($ret);
    return $ret;
}
</code></pre>

<p>Why won't this work? 
I get these errors: </p>

<p>Warning: preg_replace_callback() [function.preg-replace-callback]: Requires argument 2, 'Main::make_url_clickable_cb', to be a valid callback in line 134</p>

<p>Warning: preg_replace_callback() [function.preg-replace-callback]: Requires argument 2, 'Main::make_web_ftp_clickable_cb', to be a valid callback in line 135</p>

<p>Warning: preg_replace_callback() [function.preg-replace-callback]: Requires argument 2, 'Main::make_email_clickable_cb', to be a valid callback in  line 136</p>
