[amelius]

Why aren't exceptions used here?

Is this because the behavior is sort of "exceptional" but not so exceptional that the (supposedly inefficient) exception-mechanism is warranted?

In that case, I think the compiler should handle this case still. Using profiling, it could determine which exceptions are really exceptions and which ones are not.

[steveklabnik]

Rust doesn't have exceptions.

[amelius]

Interesting. This is certainly new for me :)