Symfony Dependency injection to class - symfony

Question

I have a class in App\Util which needs the MailerInterface Dependency. So I added it directly to the constructor like this:
public function __construct(MailerInterface $mailer)
{
$this->mailer = $mailer;
}
Then I added the argument in the services.yaml:
services:
...
App\Util\OwnerMailValidation:
arguments: ['#mailer']
In the end I used exactly the same code as provided by the symfony documentation but I keep getting the error:
Too few arguments to function App\Util\OwnerMailValidation::__construct(), 0 passed [...] 1 expected
My complete servicey.yaml:
services:
_defaults:
autowire: true
autoconfigure: true
App\:
resource: '../src/'
exclude:
- '../src/DependencyInjection/'
- '../src/Entity/'
- '../src/Kernel.php'
- '../src/Tests/'
App\Controller\:
resource: '../src/Controller/'
tags: ['controller.service_arguments']
App\Util\OwnerMailValidation:
class: App\Util\OwnerMailValidation
arguments: ['#mailer']

Answer 1

If you have a single implementation of MailerInterface you shouldn't write anything in your service.yaml
Symfony can figure it out on his own.
If it still doesn't work try to do this
App\Util\OwnerMailValidation:
arguments:
$mailer: '#<the class that implements MailerInteface that you want to inject>'
As #cerad said autowiring works if you inject your class into another.
If you're doing $validation = new OwnerMailValidation(); it just won't work because it requires a MailerInterface in the constructor.
You should inject your OwnerMailValidation into the controller method or into the class constructor.

Answer 2

Try this config:
services:
...
App\Util\OwnerMailValidation:
class: App\Util\OwnerMailValidation