PHP如何使用字符串实例化类别名

Question

I know I can do this without the alias, but in this case trying to instantiate the object using an alias attempts to find a class by the alias name. Can this not be done in PHP?

// Import of manager, admin, etc login PageObjects
use Page\Acceptance\Users\Login as ManagerLoginPage;
use Page\Acceptance\Admins\Login as AdminLoginPage;

...

// Login user type snippet
$alias= $userType . 'LoginPage'; // produces ManagerLoginPage
$User = new $alias($this); // tries to instantiate a class named 'ManagerLoginPage', which doesn't exist

$User->{'loginAs' . $userType}($user);

Answer 1

As the documentation explains:

The ability to refer to an external fully qualified name with an alias, or importing, is an important feature of namespaces. This is similar to the ability of unix-based filesystems to create symbolic links to a file or to a directory.

And several paragraphs below:

Importing is performed at compile-time, and so does not affect dynamic class, function or constant names.

This means that when you write:

use Page\Acceptance\Users\Login as ManagerLoginPage;
$page = new ManagerLoginPage();

PHP expands the aliases during the compilation to:

$page = new \Page\Acceptance\Users\Login();

You have to put the complete class name (including all the containing namespaces) into the variable $alias to make it work:

$alias = 'Page\Acceptance\Users\Login';
$User = new $alias($this);