preg_replace_callback requires argument 2 to be a valid callback... Stuck!

Question

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 $matches[1] . "<a href=\"$url\" rel=\"nofollow\">" . $this->truncate($url, 35, '...'). "</a>" . $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 $matches[1] . "<a href=\"$dest\" rel=\"nofollow\">$dest</a>" . $ret;
}

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

Why won't this work? I get these errors:

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

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

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

Answer 1

If you pass a single string as callback, PHP will interpret it as a function's name -- and Main::make_web_ftp_clickable_cb is not a valid function name;

If you want to specify a static method of a class as callback, you must use :

array('Main', 'make_web_ftp_clickable_cb')

And, if you want to specify a method of an object, instance of a class, you'll have to use :

array($object, 'make_web_ftp_clickable_cb')

Here is the relevant section of the manual : Pseudo-types and variables used in this documentation - callback

Answer 2

You need to specify your functions as static functions, and use the following as callback function:

array(get_class($this), 'make_url_clickable_cb')

array(get_class($this), 'make_web_ftp_clickable_cb')

array(get_class($this), 'make_email_clickable_cb')

or (if calling from another calss):

array('class_name', 'make_url_clickable_cb')

array('class_name', 'make_web_ftp_clickable_cb')

array('class_name', 'make_email_clickable_cb')