Support service sources

[gracicot]

Right now, the container has only one allocation strategy and one way to store services. What if one would like to control how services are allocated and where they are contained? We should explore solutions that would allow that.

[gracicot]

We could provide a constant time access service source. Right now the unordered map is fast, but not as fast as a constant time access. This will be done when supporting service source, or wathever name we find for that.

[gracicot]

In dev-4.2.x, the container is pretty much decoupled from the storage strategy. However, the interface between the container and the source is quite unclear and assumes many things.

[gracicot]

In dev-4.2.x , the container is now separated from the storage strategy. The interface between the two is now clear. We won't ship customizable service source right now because doing so is not trivial. The kgr::container_service cannot be as trivial as it is today and might need type erasure to support our current injection model. This might go into 5.0.0.

[gracicot]

Kangaru 5 is based on sources. I think it's safe to close this issue. Custom sources are containers are service definition. They are all composable and customizable.