hhvm/hphp/test/quick/hopt-static.php

<?php

class Foo {
  public static $z = 0;

  public static function setZ($a) {
    Foo::$z = $a;
  }

  public static function getZ() {
    return Foo::$z;
  }
}

$a = new Foo();

$a->setZ(4);

var_dump($a->getZ());