title: Lazy loading dependencies with symfony DI
body: <p>Currently I've got a Symfony2 DI container instance ready with a service and all it's dependencies. Lets say for example I have a Car class and it has Engine and Lights as dependencies. </p>
  
  <p>In my current setup both these dependencies are automatically created through setter injection when the Car object is created, but it might very well be that my Car object won't need it's lights this time around thus it doesn't explicitly need to create an instance of this dependency.</p>
  
  <p>Is there a way to achieve this in Symfony DI? Thus only creating an instance of the Lights object when needed? My guess is it'll be some sort of Proxy implementation like Doctrine has but as far as i've seen it doesn't exist in Symfony DI.</p>