Maybe I misunderstand what you meant, but by having `first()` return an `Option`, you can verify at compile-time that the caller handles the empty case, whereas

Maybe I misunderstand what you meant, but by having `first()` return an `Option`, you can verify at compile-time that the caller handles the empty case, whereas an assertion would not detect the issue until runtime. If the caller wants to kill the program when its empty, they can just call `.unwrap()` on the option to explicitly opt-in to a runtime check.