Interesting facts about namespaces

I found an interesting question. Within a file without a namespace.

<code>use PDO; 或者 use \PDO;
$conn = new PDO(....);
会报出一个错误 Warning: The use statement with non-compound name 'PDO' has no effect......

然而下面几种做法不会报这个错误
use PDO as PDO;
use \PDO as PDO;
或者
直接 $conn = new PDO(....);
$conn = new \PDO(....);
都是不会报错的。
</code>

Then the question comes, why can’t you use PDO for files without namespace;

Updated on July 11, 2016 22:18:51 ----------
The above test is in the php7 environment.
It is possible to use PDO in 5.4 environment, but use PDO still doesn’t work

Reply content:

I found an interesting question. Within a file without a namespace.

<code>use PDO; 或者 use \PDO;
$conn = new PDO(....);
会报出一个错误 Warning: The use statement with non-compound name 'PDO' has no effect......

然而下面几种做法不会报这个错误
use PDO as PDO;
use \PDO as PDO;
或者
直接 $conn = new PDO(....);
$conn = new \PDO(....);
都是不会报错的。
</code>

Then the question comes, why can’t you use PDO for files without namespace;

Updated on July 11, 2016 22:18:51 ----------
The above test is in the php7 environment.
It is possible to use PDO in 5.4 environment, but use PDO still doesn’t work

http://stackoverflow.com/questions/9317022/troubleshooting-the-use-statement-with-non-compound-name-has-no-effect