Its non-trivial and it could be written simpler (the tuples part could get its own type alias, making it more readable and shorter), but its not particularly ba

Its non-trivial and it could be written simpler (the tuples part could get its own type alias, making it more readable and shorter), but its not particularly bad or good. You will find examples of this mostly in libraries, but rarely its something a beginner would write. You can actually do a lot without ever using lifetimes. Eventually you'll need to learn to read this though, and its just a matter of getting used to it. I'd say none of those is any harder to understand then let say nested list comprehension in python.