Symfony __construct usage - php

Question

I am relatively new to Symfony (version 4) and trying to implement the __construct method for dependency injection.
Currently, I am "injecting" dependencies via my own implementation (before I was aware of the __construct method) like so:
routes.yaml
fetch:
path: /fetch/{req}
controller: App\Controller\Fetch::init
requirements:
req: ".+"
/fetch route calls the init() method, which serves as the constructor.
Controller Class
namespace App\Controller;
use Symfony\Component\HttpFoundation\Response;
use App\Services\Utilities; // a bunch of useful functions
class Fetch extends BaseController {
private $u;
public function init(Utilities $u) {
$this->u = $u; // set the $u member with an instance of $u
}
private function do_fetch(){
$this->u->prettyprint('hello service'); // use one of $u's methods
}
}
If you would indulge me, I came up with this ad-hoc scheme before reading the docs, which detail this almost exactly (I get a cookie).
The one difference is that the docs use __construct() in place of my init() method. The following is an example from the doc page linked above:
// src/Service/MessageGenerator.php
use Psr\Log\LoggerInterface;
class MessageGenerator
{
private $logger;
public function __construct(LoggerInterface $logger)
{
$this->logger = $logger;
}
public function getHappyMessage()
{
$this->logger->info('About to find a happy message!');
// ...
}
}
But when I swap init() for __construct(), and update the routes.yaml, I get an error.
// .....
class Fetch extends BaseController {
private $u;
public function __construct(Utilities $u) {
$this->u = $u; // set the $u member with an instance of $u
}
// ....
fetch:
path: /fetch/{req}
controller: App\Controller\Fetch::__construct
requirements:
req: ".+"
Its asking me to provide an argument to __construct since that method takes one ($u) but this was not the case when init() was acting as the constructor.
Moreover, I feel like since the __construct() method is a built-in hook, Symfony should know to use it without my having to explicitly tell it to in routes.yaml. However, excluding it throws an error as well.
routes.yaml (__construct not explicitly indicated)
fetch:
path: /fetch/{req}
controller: App\Controller\Fetch
requirements:
req: ".+"
What am I missing here?

Answer 1

__construct is a magic method in PHP. The problem with your init method is that it does not enforce that the object must have an instance of the object you need in order to be built. Sometimes an object property will not be needed. In this case, I recommend creating a setter as a way to optional set that property.Try to make your class properties private, and only allow them to be mutated or retrieved through setters and getters...this will provide a standard API to your obejct, and avoid random state manipulation.
You can use the DIC in Symfony's router to construct your controller instead of extending the base controller class by registering your controllers as services. This greatly decouples you code and allows all kinds of additional flexibility. You should always favor composition over inheritance.