Passing a class, method and arguments to WordPress functions

When adding pages to the WordPress admin you use add_menu_page, which accepts a callable function/method.

class Foo
{
    public function __construct()
    {
        add_menu_page($page_title, $menu_title, $capability, $menu_slug, [$this, 'bar'], $icon_url, $position);
    }

    public function bar(): void
    {
        echo 'Hello, World!';
    }
}

My issue is, I’m a little stumped on how to pass an argument to bar when it accepts/expects parameters, for example:

class Foo
{
    public function __construct()
    {
        add_menu_page($page_title, $menu_title, $capability, $menu_slug, [$this, 'bar'], $icon_url, $position);
    }

    public function bar(string $name = ''): void
    {
        echo "Hello, {$name}!";
    }
}

I’ve tried a couple different approaches but I can’t seem to get it to work:

[$this, 'bar', 'Bob']; // Warning: call_user_func_array() expects parameter 1 to be a valid callback, array must have exactly two members in /wp-includes/class-wp-hook.php on line 287

[$this, ['bar', 'Bob']] // Warning: call_user_func_array() expects parameter 1 to be a valid callback, second array member is not a valid method in /wp-includes/class-wp-hook.php on line 287

So looking at line 287 of that file, it’s using call_user_func_array and I think it seems as if it’s possible to pass an argument in the $function parameter of add_menu_page but I just cannot get it to work:

// Avoid the array_slice() if possible.
if ( 0 == $the_['accepted_args'] ) {
    $value = call_user_func( $the_['function'] );
} elseif ( $the_['accepted_args'] >= $num_args ) {
    $value = call_user_func_array( $the_['function'], $args );
} else {
    $value = call_user_func_array( $the_['function'], array_slice( $args, 0, (int) $the_['accepted_args'] ) );
}

Help would be appreciated!

Answer

You should be able to pass an anonymous function instead, whose body would simply call the bar method with the appropriate arguments.

The anonymous function would look like this:

function () { $this->bar('Bob'); }

Or alternatively, if you’re using PHP 7.4+:

fn() => $this->bar('Bob')

So, just pass that as the callback, like this:

add_menu_page(
  $page_title,
  $menu_title,
  $capability,
  $menu_slug,
  // fn() => $this->bar('Bob'),
  function () {  
    $this->bar('Bob');  
  },
  $icon_url,
  $position
);

Note: I’m very unfamiliar with WordPress so this might not be the most appropriate way to do this.