[physPop]

Yes because injecting nowFn is trivial and not a case for DI. Consider a database handle, or network socket, or http response payload. Clearly each class shouldn't be making its own version of those.

[loevborg]

You're right, stateful dependencies like DB handles need to be passed in manually, and that's a bit of extra legwork you need to do.

[Charon77]

Just use a static variable to the DB instance / pool, maybe using singletons, so everyone needing it have access.

[cyanydeez]

You're nitpicking for no good reason. You can create global handles to each of those items, and let them instantiate with the class or override them with a create function.

Dependency injection boils down the question of whether or not you can dynamically change a dependency at runtime.