Can we add Twig globals ?

[cgweeratunga]

Hi,
Can we add Twig globals like Symfony in yml ?

twig:
# ...
globals:
ga_tracking: UA-xxxxx-x

I've added it like above( same as Symfony2 ) but got error message.

Catchable fatal error: Argument 1 passed to Igorw\Silex\ConfigServiceProvider::mergeRecursively() must be of the type array, object given