$o1 = ion\unserialize("[foo,{p:1}]");
$o2 = ion\unserialize("[foo,{p:1}]", $u1 = new ion\Unserializer\PHP);
$o3 = ion\unserialize("[foo,{p:1}]", $u2 = new ion\Unserializer\PHP(new ion\Reader\Options));
$o1 = ion\unserialize("[foo,{p:1}]");
$o2 = ion\unserialize("[foo,{p:1}]", $u1 = new ion\Unserializer\PHP);
$o3 = ion\unserialize("[foo,{p:1}]", $u2 = new ion\Unserializer\PHP(new ion\Reader\Options));