How to pass a parameter to this add_filter example

Question

I have a class with this function to provide a user language based on $user_id

function provide_user_language($user_id) {

return apply_filters('get_user_language',$user_id);

}

So in my script, I can simply get the user language by doing this:

$user_language=$this->provide_user_language($user_id);

But I need to associate this $user_language to a "set_current_language". I can do this by doing an add filter hook, but add_filter does not accept parameters. This is the add_filter line with the function itself but I don't know how to pass the $user_id or the $user_language so that set_current_language will be set to $user_language:

add_filter('set_current_language', array(&$this,'provide_user_language')); 

I tried following this one but it won't work:

Passing a parameter to filter and action functions

I appreciate any tips. Probably there is an easy way.

Answer 1

The trick Toscho used was to get around the problem using Objects.

So lets say we have a filter named xyz, that passes in some post content. The goal of this hypothetical scenario is to append a word to the content that we can not "hardcode".

Here's the basic filter:

add_filter( 'xyz', 'test' );
function test( $content ) {
    return $content;
}

So we append to $content, but how do we get the value to append? That is the crux of your issue.

To solve this problem you can use OOP:

class test_object {
    public $appended_value = '';
    function test( $content ) {
        return $content.$this->appended_value;
    }
}

$obj = new test_object();
$obj->appended_value = 'hello world';
add_filter( 'xyz', array( $obj, 'test' ) );

Here the class/object is being used to store the extra data.

An alternative to this would be to use a closure ( not a lambda function ) to create a new function based on a value, but this will not work prior to PHP 5.3, e.g.:

add_filter('xyz', 
    function($content) use ($appended_value) {
        return $content.$appended_value;
    }
);

Disclaimer: None of this code is copy paste, it is for demonstrative purposes.

Answer 2

Thanks Tom, Unfortunately Toscho concept didn't work for me, so I dig deeper in the add filter documentation here: http://codex.wordpress.org/Function_Reference/add_filter and they allow anonymous functions as callback.

This method finally solved my problem. This is how I resolve this one for other users that are experiencing this issue:

add_filter('set_current_language', 
    function($lang_set) use ($user_language) {
    $lang_set=$user_language;
    return $lang_set;
});

In this method, I pass the $user_language(which is available) to the add_filter hook. $lang_set is the dummy variable used to return the callback output.

I have finally set the "set_current_language" to the user language using add_filter.