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WP_Hook::add_filter( string $tag, callable $function_to_add, int $priority, int $accepted_args )

Hooks a function or method to a specific filter action.

Parameters

$tag

(string) (Required) The name of the filter to hook the $function_to_add callback to.

$function_to_add

(callable) (Required) The callback to be run when the filter is applied.

$priority

(int) (Required) The order in which the functions associated with a particular action are executed. Lower numbers correspond with earlier execution, and functions with the same priority are executed in the order in which they were added to the action.

$accepted_args

(int) (Required) The number of arguments the function accepts.

Source

File: wp-includes/class-wp-hook.php 

public function add_filter( $tag, $function_to_add, $priority, $accepted_args ) {
		$idx = _wp_filter_build_unique_id( $tag, $function_to_add, $priority );

		$priority_existed = isset( $this->callbacks[ $priority ] );

		$this->callbacks[ $priority ][ $idx ] = array(
			'function'      => $function_to_add,
			'accepted_args' => $accepted_args,
		);

		// If we're adding a new priority to the list, put them back in sorted order.
		if ( ! $priority_existed && count( $this->callbacks ) > 1 ) {
			ksort( $this->callbacks, SORT_NUMERIC );
		}

		if ( $this->nesting_level > 0 ) {
			$this->resort_active_iterations( $priority, $priority_existed );
		}
	}

Changelog

Version Description
4.7.0 Introduced.

© 2003–2019 WordPress Foundation
Licensed under the GNU GPLv2+ License.
https://developer.wordpress.org/reference/classes/wp_hook/add_filter