Hard Unregister for an Object's callback where you do not have access to the instance itself.

hard-unregister.php

/**
 * Do a hard unregister of an object's callback for the specified event name
 * and priority level.
 *
 * In WordPress, the callback key (or unique ID) is generated using the hash ID of
 * the object concatenated with the method name.  In the event that you do not have
 * the object itself, then we use this hard approach to first first the callback
 * function and then do the remove.
 *
 * This process works for both filter and action events.
 *
 * @since 1.0.0
 *
 * @param string $event_name The name of the filter or action event
 * @param integer $priority Priority level
 * @param string $method_name Callback's method name
 *
 * @return void
 */
function do_hard_unregister_object_callback( $event_name, $priority, $method_name ) {
	$callback_function = get_object_callback_unique_id_from_registry( $event_name, $priority, $method_name );
	if ( ! $callback_function ) {
		return false;
	}

	remove_filter( $event_name, $callback_function, $priority );
}

/**
 * Get the object's event registry unique ID for the given event name, priority
 * level, and method name.
 *
 * @since 1.0.0
 *
 * @param string $event_name The name of the filter or action event
 * @param integer $priority Priority level
 * @param string $method_name Callback's method name
 *
 * @return string|boolean
 */
function get_object_callback_unique_id_from_registry( $event_name, $priority, $method_name ) {
	global $wp_filter;

	if ( ! isset( $wp_filter[ $event_name ][ $priority ] ) ) {
		return false;
	}

	foreach( $wp_filter[ $event_name ][ $priority ] as $callback_function => $registration ) {

		if ( strpos( $callback_function, $method_name, 32) !== false) {
			return $callback_function;
		}
	}

	return false;
}

Line 50 if ( strpos( $callback_function, $method_name, 32) !== false) {} is just one way to do it. The other way is to look into the registration at the function and check the class and method names directly.

Found this really helpful. Thanks for this!

I found that I was hitting $callback_function strings that did not contain a 32 char long prefix. So I edited the get_object_callback_unique_id_from_registry like below to suppress warnings.

function get_object_callback_unique_id_from_registry( $event_name, $priority, $method_name ) {
	global $wp_filter;

	if ( ! isset( $wp_filter[ $event_name ][ $priority ] ) ) {
		return false;
	}

	foreach( $wp_filter[ $event_name ][ $priority ] as $callback_function => $registration ) {
		if(strlen($callback_function) > 32) {
			if ( strpos( $callback_function, $method_name, 32) !== false) {
				return $callback_function;
			}
		}
	}

	return false;
}
...

@ljsherlock - That improves it. Good job.

We strive to keep code levels shifted to the left as much as possible. Right? How can we reduce the levels with the new check? There are a couple strategies.

Option 1: Convert the check into a guard clause like this, where it skips if the string's length is not more than 32.

   foreach ( $wp_filter[ $event_name ][ $priority ] as $callback_function => $registration ) {
   	# Skip if the callback function's strlen is <= 32.
   	if ( strlen( $callback_function ) <= 32 ) {
   		continue;
   	}

   	if ( strpos( $callback_function, $method_name, 32 ) !== false ) {
   		return $callback_function;
   	}
   }

Option 2: Combine the checks.

	foreach ( $wp_filter[ $event_name ][ $priority ] as $callback_function => $registration ) {
		if ( strlen( $callback_function ) > 32 && strpos( $callback_function, $method_name, 32 ) !== false ) {
			return $callback_function;
		}
	}