查看CI_Loader类对您引用的library（）方法的签名：

Check out the CI_Loader class's signature for the library() method you refer to:

/**
 * Class Loader
 *
 * This function lets users load and instantiate classes.
 * It is designed to be called from a user's app controllers.
 *
 * @access  public
 * @param   string  the name of the class
 * @param   mixed   the optional parameters
 * @param   string  an optional object name
 * @return  void
 */
function library($library = '', $params = NULL, $object_name = NULL)
{

它返回void，所以当然你设置的返回值为null。我想你对该方法的目的感到困惑。它加载库并将其附加到codeigniter超级对象，以便您可以引用它：

It returns void, so of course whatever you set the return value to will be null. I think you're confused about the purpose of that method. Its to load the library and attach it to the codeigniter super-object, so that you can reference it as:

$this->CI->[library name]

在您的情况下，到新加载的库（一些特定的验证器库，我基于你的代码片段猜测）：

In your case, you'll just want to refer to the newly-loaded library (some specific validator library I'm guessing based on your code snippet) in the usual way:

$this->CI->[newly loaded super awesome validator library]