I have an add_filter function for the auth_cookie_expiration hook. This hook accepts three parameters. However, I am interested 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;
}

I have an add_filter function for the auth_cookie_expiration hook. This hook accepts three parameters. However, I am interested 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;
}

• filters
• hooks
• cookies

• 1 you cannot modify the argument numbers then the use of use looks like the better solution. – mmm Commented Jan 3, 2018 at 16:06
• 1 what is not elegant about closures? by miles better than creating an object for this or using globals. – Mark Kaplun Commented Jan 3, 2018 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 Commented Jan 3, 2018 at 16:19

3 Answers 3

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;
}

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.

After just using my original "solution" for a while, I have returned to this problem with a bit more time to figure out what WordPress actually does.

Firstly it should be noted that to directly pass a parameter to an add_filter function, the only reasonable way is the one in my original question.

However, more often than not, it is possible to solve the larger problem better by passing a parameter to the function calling apply_filters in WordPress or the plugin you're trying to hook into.

For example, apply_filters( 'auth_cookie_expiration' ), in any meaningful way for hooking, is called in WordPress inside wp_set_auth_cookie, which accepts the same parameters ( $user_id, $remember ), so calling wp_set_auth_cookie() (likely done anyway for any session manipulation) allows the eventual passing of parameters to add_filter. For example:

add_filter( 'auth_cookie_expiration', array( 'get_session_expiration' ), 10, 3 );

// ...

wp_set_auth_cookie( $user_id, $is_remember_me );

// ...

function get_session_expiration( $expiration, $user_id, $remember ) {
    // ...
    return $some_calculated_expiration;
}

This works in multiple cases I have found where filter hooks are available.