PHP: Calling a custom sort function from an object?

Question

PHP

In PHP there is such a function: The name of the function that will take the next pair of values ​​​​and compare them is passed to it as the second parameter. There is a regular PHP class:
bool usort ( array &array, callback cmp_function )

namespace MyProj;

class Test {
  public function sortDir($a,$b)
  {
    if(is_dir($a['path']) && !is_dir($b['path'])) return -1;
    if(!is_dir($a['path']) && is_dir($b['path'])) return 1;
    if($a['name']<$b['name']) return -1; elseif($a['name']>$b['name']) return 1; else return 0;
  }
  
  public function getList()
  {
    $dir[0] = array('path' => '/home/www', 'name' => 'www');
    $dir[1] = array('path' => '/home/www/css', 'name' => 'css');
    $dir[2] = array('path' => '/home/www/test.txt', 'name' => 'test.txt');
    $dir[3] = array('path' => '/home/www/css/main.css', 'name' => 'main.css');
    
    usort($dir, 'sortDir');
  }
}

$obj = new Test();
$obj->getList();

Here's how to correctly call <b>usort($dir, 'sortDir')</b>in one of the last lines? What options I have not tried, it always gives out:

Warning: usort() expects parameter 2 to be a valid callback, function 'sortDir' not found or invalid function name

Answer 1

usort($a, array("Test", "sortDir"));

Answer 2

documentation to help
www.php.net/manual/en/language.pseudo-types.php#language.types.callback

Answer 3

Try
usort($dir, array("this", "sortDir"));
or
usort($dir, array("Test", "sortDir") );

Answer 4

usort($dir, array($this, "sortDir") );

Answer 5

usort($dir, 'self::sortDir');
or
usort($dir, 'MyProj\Test::sortDir');