Using Dependency Injection in Magento 1?

Question

I would love to use Magento 2's DI in some of my Magento 1 modules.

I'm not entirely sure how can I approach that and more importantly, if Magento 1 will allow me to do so ?

Most of the M1 classes extend Varien_Object. Thus, would injecting the classes the exact same way as M2 be enough to start using DI on M1 ? Something like this:

class Vendor_Module_Model_Test extends Mage_Core_Model_Abstract {
 protected $_productCollection;
 public function __construct(
 Mage_Catalog_Model_Resource_Product_Collection $productCollection
 ) {
 $this->_productCollection = $productCollection;
 parent::__construct();
 }
 public myFunction($productId)
 {
 return $this->_productCollection->addIdFilter($productId);
 }
}

Answer 1

The biggest question here would be do you need the Mage_Core_Model_Abstract class and an parent?

How I treat DI in Magento 1.

1. If I need the class to be a "Magento" class as in Mage::getModel('my/class') then I will not do di as it will not work with __construct so well.
2. If I do not need the class to be a "Magento" class then I will instantiate it with new Class() and I can pass in the DI.

Think about your classes if they really need to be Magento classes and pick the option that fits best for you.