Magento 2: How to add a class to an observer without construct

Question

I am making this observer class to check if a visitor is logged in.

use Magento\Framework\Event\ObserverInterface;
use Magento\Customer\Model\Session;

class CheckLoginObserver implements ObserverInterface
{
  /**
   * @var \Magento\Customer\Model\Session
   */
  protected $customerSession;

  public function execute(\Magento\Framework\Event\Observer $observer)
  {
    //use $customerSession variable here
    ...
  }

The goal is to use the $customerSession class in the execute function. What's the right way to do that?

Answer 1

It depends. Which event are You using for that observer? There is possibility that You can use customer session from Observer. Of course You can check it by look what contain $observer (by using xdebug).
If observer doesnt contain that, You have to use __construct function to load customerSession.