PHP json_encode 转换成空对象和空数组

$foo = array(
  "bar1" => array(), 
  "bar2" => array() 
);

{
  "bar1": {},
  "bar2": []
}

{
  "bar1": [],
  "bar2": []
}

{
  "bar1": {},
  "bar2": {}
}

$foo = array(
  "bar1" => new stdClass(), // Should be encoded as an object
  "bar2" => array() // Should be encoded as an array
);

echo json_encode($foo);

$foo = array(
  "bar1" => (object)array(), // Should be encoded as an object
  "bar2" => array() // Should be encoded as an array
);

echo json_encode($foo);
// {"bar1":{}, "bar2":[]}