<?php
class A
{
  function get($class)
  {
    return new $class;
  }
}

class B extends A
{
  function get()
  {
    return parent::get(__CLASS__);
  }
  function hi()
  {
    echo "hi";
  }
}

$b = B::get();
$b->hi();
var_dump($b);
?>