__construct上的语法错误，如果我使用ClassName作为构造函数签名，则有效

Question

当我创建此类的实例时，我收到错误

Parse error: syntax error, unexpected '__construct' (T_STRING), 
expecting variable    (T_VARIABLE) on line 9. 

这是我创建实例的方式：

    function controller_from_str($controller_name)
    {
        $controllers_namespace = 'MVCBP\\Controllers\\';
        $controller = $controllers_namespace 
            . $controller_name . 'Controller';

        return new $controller();
    }

如果我将__construct()更改为UserController()，则此功能正常。我在Windows 7上使用PHP 5.4这是预期的行为吗？

这是我的班级：

<?php
namespace MVCBP\Controllers;

use MVCBP\Core as Core;
use MVCBP\Models as Models;
use MVCBP\Repositories as Repos;

class UserController implements Core\ControllerInterface
{
    private $UserRepo;

    public function __construct()
    {
        $this->UserRepo = new Repos\UserRepository();
    }

    public function Index()
    {
        echo '<h1>User</h1>';
    }

    public function Create()
    {
        //TODO: if GET/POST
        $user = new Models\User();
        /*var_dump($user->getDb());*/
        render_view('User/Create');
    }

    private function CreateGet()
    {

    }

    private function CreatePost()
    {

    }
}