I would not consider setting an exit code to be a fancy feature, but I guess we are living on the bleeding edge here :)
EDIT: I should have said explicitly in my initial comment that I knew about std::process::exit and panic!, but did not consider them to be a clean solution for exiting the program under normal circumstance -- more of an abort() mechanism.
I don't see why. process::exit is perfectly clean from my perspective. You don't need to be on the bleeding edge. This has been possible since Rust 1.0.
EDIT: I should have said explicitly in my initial comment that I knew about std::process::exit and panic!, but did not consider them to be a clean solution for exiting the program under normal circumstance -- more of an abort() mechanism.