gistfile1.php

class foo {
  public $foo = 123;
  public function test() {
    test($this);
    print $this->foo;
  }
}

function test(foo $foo) {
  $new_foo = new foo();
  $new_foo->foo = 'hey';

  $foo = $new_foo;
}

$foo = new foo();
$foo->test();