How does array(__CLASS__, work in wordpress? - php

Question

I'm trying to mod a wordpress plugin to take custom categories. So when the random_post_link is called, I can add the custom category by using random_post_link('Random Link',3). 3 being the category name.
How does the plugin below create a new object of class Random_Post_Link? I thought you created new objects by doing something like:
$a = new random_post_link;
But I don't see that in the plugin. I think it creates the new object in the init function by using a hook:
add_action('init', array(CLASS, 'jump'));
If that's the case, how can I add parameter to jump function?
I think I know how add_action works, the second parameter should be the function name, how does
" array(CLASS, 'jump')" work?
Here's the full code for the plugin:
function random_post_link($text = 'Random Post',$the_cat = 36) {
printf('%s', get_random_post_url(), $text);
$the_category = $the_cat;
}
function get_random_post_url() {
return trailingslashit(get_bloginfo('url')) . '?' . Random_Post_Link::query_var;
}
class Random_Post_Link {
const query_var = 'random';
const name = 'wp_random_posts';
public $the_category;
function init() {
add_action('init', array(__CLASS__, 'jump'));
// Fire just after post selection
add_action('wp', array(__CLASS__, 'manage_cookie'));
}
// Jump to a random post
function jump() {
if ( ! isset($_GET[self::query_var]) )
return;
$args = apply_filters('random_post_args', array(
'post__not_in' => self::read_cookie(),
));
$args = array_merge($args, array(
'orderby' => 'rand',
'cat' => $the_category,
'showposts' => 1,
));
$posts = get_posts($args);
if ( empty($posts) ) {
self::update_cookie(array());
unset($args['post__not_in']);
$posts = get_posts($args);
}
if ( empty($posts) )
wp_redirect(get_bloginfo('url'));
$id = $posts[0]->ID;
wp_redirect(get_permalink($id));
die;
}
// Collect post ids that the user has already seen
function manage_cookie() {
if ( ! is_single() )
return;
$ids = self::read_cookie();
$id = $GLOBALS['posts'][0]->ID;
if ( count($ids) > 200 )
$ids = array($id);
elseif ( ! in_array($id, $ids) )
$ids[] = $id;
self::update_cookie($ids);
}
private function read_cookie() {
return explode(' ', #$_COOKIE[self::name]);
}
private function update_cookie($ids) {
setcookie(self::name, trim(implode(' ', $ids)), 0, '/');
}
}
Random_Post_Link::init();

Answer 1

Some WordPress authors use the Class structure in PHP to basically reduce global vars. The class is meant as a 'singleton' of sorts, and so it isn't usually instantiated (that code calls Random_Post_Link::init(); at the bottom instead). The class functions are treated as Class members, not instance members, sort of like Math.max() in other languages, for example.
The __CLASS__ php keyword is simply a token for the current class, so when passed, the callable becomes Random_Post_Link::method() or array( 'Random_Post_Link', 'method' )
If you need to unhook, try remove_action( 'init', array( 'Random_Post_Link, 'jump' ) );
(Also note, that methods used that way should be declared static function jump() {...})
P.S. To further clarify:
http://php.net/manual/en/language.types.callable.php
The array('class', 'function') syntax is a PHP thing, while WordPress actions expect a callable which could be any of the PHP callable things.