[p1necone]

Imo always expect rather than unwrap in those cases. If it's justifiable, you should justify it in the message.

("This should never happen because: ..., if you see this message there's a bug.")

[Arnavion]

Or let-else with a panic!() in the else {} if you want to use a format string.

[xigoi]

If you’re doing something like Project Euler, writing error messages is a waste of time.