As the Symfony2 documentation describes, it's possible to inject an "expression language" string as a service argument, but it apperently doesn't work, even with a simple implementation :
services:
my_service:
class: AAA\BBBBundle\ClassName
arguments: ["@=container.hasParameter('param_name') ? parameter('param_name') : 'default_value'"]
i got:
Fatal error: Uncaught exception 'Symfony\Component\DependencyInjection\Exception\ServiceNotFoundException' with message 'The service "my_service" has a dependency on a non-existent service "=container.hasparameter('some_param') ? parameter('some_param') : 'default_value'".' in /[...]/symfony/symfony/src/Symfony/Component/DependencyInjection/Compiler/CheckExceptionOnInvalidReferenceBehaviorPass.php on line 59
have i missed something ?