register_setting backwards compatibility when function defined after registration

[ItayXD]

to make register_setting backward compatible this code is used:

    if ( is_callable( $args ) ) {
        $args = array(
            'sanitize_callback' => $args,
        );
    }

so if you call register_setting with a function instead of args, and only then define that function is_callable returns false, and the function is never passed.

[markparnell]

Thanks for the report @ItayXD and sorry it's taken so long for you to get a response! What you're asking for is making improvements to what is effectively a deprecated API - and I'm not sure it's even possible with PHP.

You should just use the newer array format for the $args parameter to pass your callback instead.