Is that valid to use private static callbacks in PHP?

Question

This works:

class MyClass {
  private static $data = array( 'banana', 'cherry', 'apple' );

  private static function sort_by_text( $first, $second ) {
    return strcasecmp( $first, $second );
  } 

  public static function sorted_data() {
    usort( self::$data, array( __CLASS__, 'sort_by_text' ) );
    return self::$data;
  }
}

print_r( MyClass::sorted_data() ); 
// Array ( [0] => apple [1] => banana [2] => cherry ) 

But, PHP docs always use public callbacks.

Is the fact that callbacks can be private just not documented well, or making them private can lead to issues?

Answer 1

Callbacks are context aware and you can see that there are some bugs around it, like: https://bugs.php.net/bug.php?id=62547

https://bugs.php.net/bug.php?id=63468

But it is being fixed and therefore is supported :)