Is it possible to add an argument to a custom function added to a filter hook?

Question

Example: I'm trying to modify an instantiation of WP_Query by using the posts_orderby filter like so:

add_filter('posts_orderby', 'favorites_orderby');
$new_query = new WP_Query($args);
remove_filter('posts_orderby', 'favorites_orderby');

the favorites_orderby() function is like so:

function favorites_orderby($post_in){
    if(is_array($post_in))
        $post_in_str = implode(',', $post_in);
    return $post_in_str;
}

$post_in is an array that changes based on a previous, separate db query, so I need to be able to pass it into the favorites_orderby() function. Basically it's an array of post IDs that need to get fed to the WP_Query instantiation's ORDER BY parameter so that the resulting db request is set like so: ORDER BY FIELD(ID, 6, 18, 90, 12).

Everything works except passing the array of post IDs ($post_in) to the favorites_orderby()

Any help would be greatly appreciated!

Answer 1

No, filters get arguments based on the call to the filter. Basically, filters get their inputs from the apply_filters function call.

If you want to pass in data via another means, use a global variable or wrap the code and the data you want to use in an instance of a class.