PHP：Cannot use object of type stdClass as array

$json = '{"name": "Tom", "age": 23}';

$data = json_decode($json);
// 取值方式
// 错误
// print_r($data['name']);
// Cannot use object of type stdClass as array
// 正确
print_r($data->name); // Tom
print_r($data->age); // 23
print_r(gettype($data)); // object
print_r($data);

stdClass Object
(
    [name] => Tom
    [age] => 23
)

$data = json_decode($json, true);
// 取值方式
// 错误
// print_r($data->name);
// Trying to get property of non-object
// 正确
print_r($data['name']); // Tom
print_r($data['age']); // 23
print_r(gettype($data)); // array
print_r($data);

Array
(
    [name] => Tom
    [age] => 23
)