resolve filename another file

i now following:

class subclass extends superclass {
  duty __construct() {
    parent::__construct();
  }
}

class superclass {
  duty __construct() {
    // echoes "i'm subclass i'm fluctuating superclass"
    relate 'i\'m '.get_class($this).' i\'m fluctuating '.__class__;
  }
}

i something identical filenames (__file__, nonetheless boldly evaluated); i know record subclass resides in, superclass. illusory any glorious way?

i know something , nonetheless that's unequivocally efficient, generally i have countless instances.