add_filter_side_effect() allows attaching a callback function to a WordPress filter without requiring that the callback function return the filtered value or even return any value. It wraps add_filter() and accepts the same arguments with the same defaults.
The callback function can return void or return a value. If the callback function returns a value, that value will be ignored, not passed back to the filter. Filter side effects thus behave like add_action() callbacks and can be used in situations where a call to apply_filters() signals that some behavior needs to occur, but no convenient action exists to run it.
Install the latest version with:
$ composer require alleyinteractive/wp-filter-side-effects<?php
use function Alley\WP\add_filter_side_effect;
add_filter_side_effect(
'rest_pre_insert_post',
function ( $prepared_post, $request ): void {
// Do something before the post is saved, like...
$language_slug = $request['lang'];
$default_category = $this->get_custom_default_language_category( $language_slug );
if ( $default_category ) {
add_filter( 'pre_option_default_category', fn() => $default_category );
}
},
10,
2,
);