I have an add_filter function for the auth_cookie_expiration hook. This hook accepts three parameters. However, I am interesting in passing it more parameters. For example:

add_filter( 'auth_cookie_expiration', 'get_expiration', 10, 5 );

This would be possible with apply_filter, but the add_filter function is called once, which makes it throw an error:

PHP Fatal error:  Uncaught ArgumentCountError: Too few arguments to function get_expiration(), 3 passed in ... and exactly 5 expected

I got around this using closures, but it seems like a completely ridiculous way to do this:

add_filter( 'auth_cookie_expiration', function() use ($param1, $param2) { return get_expiration(null, null, null, $param1, $param2); } , 10, 3 );

Is there a proper/more elegant way to make it accept additional parameters (even better, the params I want in place of the default ones)? Am I misunderstanding how add_filter is supposed to work?

For the sake of example, suppose get_expiration looks like this:

function get_expiration( $length, $user_id, $remember, $param1, $param2 )
    return $param1 + $param2;
  • 1
    you cannot modify the argument numbers then the use of use looks like the better solution. – mmm Jan 3 '18 at 16:06
  • 1
    what is not elegant about closures? by miles better than creating an object for this or using globals. – Mark Kaplun Jan 3 '18 at 16:15
  • They're not inelegant in principle (on the contrary), just in this case: basically I'm creating a function within a one-liner just to call another function. It's a pretty dirty workaround for having to use a hook that doesn't handle such cases. But here I suspect I am simply missing something, and that WordPress has thought of such a scenario. Could be wrong though. – Ynhockey Jan 3 '18 at 16:19
  • Are you all serious? Discussing, which method of passing parameters by filter's callback function is proper, or more elegant, is simply ridiculous. – Frank P. Walentynowicz Jan 3 '18 at 21:48

Am I misunderstanding how add_filter is supposed to work?

Yes, you are.

The function ( aka callback function ), specified by name, in the second parameter of add_filter(), NEVER passes ANY parameters. It accepts parameters passed by apply_filters(). The number of these parameters, and their meaning is defined by apply_filters(). The callback function MUST accept at least the first parameter, past the hook name. It MUST, also, return modified ( or not ) value for this first parameter.

  • 4
    What would be a good way for this user to access an additional variable ( not originally passed to the function ) inside the callback? – Howdy_McGee Jan 3 '18 at 22:07

The second parameter in add_filter is a function with accepted arguments, not returned values.

This is an example how I pass my custom array $args to change an existing array $filter_args:

add_filter( 'woocommerce_dropdown_variation_attribute_options_args', function( $filter_args ) use ( $args ) {
        return eswc_var_dropdown_args( $filter_args, $args );

function eswc_var_dropdown_args( $filter_args, $args ) {
    $filter_args['show_option_none'] = $args['var_select_text'];
    return $filter_args;

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