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_wp_filter_build_unique_id()

_wp_filter_build_unique_id( string $hook_name, callable $callback, int $priority ): string|null

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This function’s access is marked private. This means it is not intended for use by plugin or theme developers, only by core. It is listed here for completeness.

Builds a unique string ID for a hook callback function.

Description

Functions and static method callbacks are just returned as strings and shouldn’t have any speed penalty.

Parameters

$hook_namestringrequired
Unused. The name of the filter to build ID for.
$callbackcallablerequired
The callback to generate ID for. The callback may or may not exist.
$priorityintrequired
Unused. The order in which the functions associated with a particular action are executed.

Return

string|null Unique function ID for usage as array key, or null if it couldn’t be determined.

Source

function _wp_filter_build_unique_id( $hook_name, $callback, $priority ): ?string {
	if ( is_string( $callback ) ) {
		return $callback;
	}

	if ( is_object( $callback ) ) {
		return (string) spl_object_id( $callback );
	}

	if ( ! isset( $callback[1] ) || ! is_string( $callback[1] ) ) {
		return null;
	}

	if ( is_object( $callback[0] ) ) {
		// Object class calling.
		return ( (string) spl_object_id( $callback[0] ) ) . $callback[1];
	} elseif ( is_string( $callback[0] ) ) {
		// Static calling.
		return $callback[0] . '::' . $callback[1];
	}

	return null;
}

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Used byDescription
WP_Hook::add_filter()wp-includes/class-wp-hook.php

Adds a callback function to a filter hook.

WP_Hook::remove_filter()wp-includes/class-wp-hook.php

Removes a callback function from a filter hook.

WP_Hook::has_filter()wp-includes/class-wp-hook.php

Checks if a specific callback has been registered for this hook.

Changelog

VersionDescription
7.1.0Uses spl_object_id() instead of spl_object_hash() for performance.
6.9.0Returns explicit null if an invalid callback is supplied.
5.3.0Removed workarounds for spl_object_hash().
$hook_name and $priority are no longer used, and no longer returns false, but can still return void for invalid callbacks.
2.2.3Introduced.

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