Is it recommended to use object manager by passing into constructor as a dependency? [duplicate]

Question

As of my observation, core team used the object manager as added

Example flow taken from module-cms

    public function __construct(
          //.....
          \Magento\Framework\ObjectManagerInterface $objectManager
          //.....
               ) 
                 {
                    $this->_objectManager = $objectManager;
                 }

Later used

$resultPage = $this->_objectManager->get('Magento\Cms\Helper\Page')->prepareResultPage($this, $pageId);

1. Is it recommended to use object manager like this ?
2. Why core team not passing this class directly to constructor as a dependency ?
3. Is there any specific case/reason to use the object manager like this ?

Can any one provide the detailed answer. Thanks.

Yes some of the answer can be found in the link but my questions/ambiguity not solved yet.

Answer 1

This question is clearly a duplicate but it seems like you need some clarifications.

If you do this:

$objectManager = \Magento\Framework\App\ObjectManager::getInstance();
$product = $objectManager->create('Magento\Catalog\Model\Product')->load($id);

Or if you inject the object manager in your constructor and later use it by calling:

$this->_objectManager->create('Magento\Catalog\Model\Product')->load($id);

It's exactly the same you're using the OM directly so you'll get the answers you need from the duplicate.

The exceptions are:

• in static magic methods like __wakeup, serialize, etc
• in case you should make backward compatibility of constructor
• in global scope, like in fixtures of integration test.
• in class that needs only for creation of object like factory, proxy , etc

However, as stated in one of the duplicate answers:

M2 is a port of M1 - not a complete rewrite. So don't assume that all the M2 code is perfectly ported yet (unfortunately). Just because you find something in the M2 code base, that does not mean "its the best way to do it". Sometimes it is just "we have not got around to fixing it yet".

In your particular case, I reckon that's your answer, this code has not been refactored yet, it's a leftover from when M1 was ported to M2