How to implement immutable ring buffer?

[drug via Digitalmars-d-learn]

Could somebody share his thoughts on the subject?
Would it be efficient? Is it possible to avoid memory copying to provide 
immutability? To avoid cache missing ring buffer should be like array, 
not list, so it's possible that the whole buffer should be moved. Is it 
neccessary to be real immutable, may be some form of fake immutabitiy is 
enough?
I'd like to try immutability in my app, and ring buffer is what I don't 
know how to use in the realm of immutability.

Thanks