WP_Hook

18#[AllowDynamicProperties]19final class WP_Hook implements Iterator, ArrayAccess {20 21	/**22	 * Hook callbacks.23	 *24	 * @since 4.7.025	 * @var array26	 */27	public $callbacks = array();28 29	/**30	 * Priorities list.31	 *32	 * @since 6.4.033	 * @var array34	 */35	protected $priorities = array();36 37	/**38	 * The priority keys of actively running iterations of a hook.39	 *40	 * @since 4.7.041	 * @var array42	 */43	private $iterations = array();44 45	/**46	 * The current priority of actively running iterations of a hook.47	 *48	 * @since 4.7.049	 * @var array50	 */51	private $current_priority = array();52 53	/**54	 * Number of levels this hook can be recursively called.55	 *56	 * @since 4.7.057	 * @var int58	 */59	private $nesting_level = 0;60 61	/**62	 * Flag for if we're currently doing an action, rather than a filter.63	 *64	 * @since 4.7.065	 * @var bool66	 */67	private $doing_action = false;68 69	/**70	 * Adds a callback function to a filter hook.71	 *72	 * @since 4.7.073	 *74	 * @param string   $hook_name     The name of the filter to add the callback to.75	 * @param callable $callback      The callback to be run when the filter is applied.76	 * @param int      $priority      The order in which the functions associated with a particular filter77	 *                                are executed. Lower numbers correspond with earlier execution,78	 *                                and functions with the same priority are executed in the order79	 *                                in which they were added to the filter.80	 * @param int      $accepted_args The number of arguments the function accepts.81	 */82	public function add_filter( $hook_name, $callback, $priority, $accepted_args ) {83		if ( null === $priority ) {84			$priority = 0;85		}86 87		$idx = _wp_filter_build_unique_id( $hook_name, $callback, $priority );88 89		$priority_existed = isset( $this->callbacks[ $priority ] );90 91		$this->callbacks[ $priority ][ $idx ] = array(92			'function'      => $callback,93			'accepted_args' => (int) $accepted_args,94		);95 96		// If we're adding a new priority to the list, put them back in sorted order.97		if ( ! $priority_existed && count( $this->callbacks ) > 1 ) {