[Reelin]

> Not having undefined behavior does make life easier

I have mixed feelings about this. It seems like many examples of undefined behavior are things that don't make sense to do (ie ought to result in an error) which would often be undecidable at compile time. Runtime error checks would incur performance penalties so it's up to to programmer to include them.

The borrow checker is an obvious advantage here. Beyond that, I guess you could do many of the same things in unsafe blocks and they could cause problems just as easily. If they end up breaking things no one will blame the language because the tin was clearly labeled.

I do prefer language designs that make it possible to write things that are safe by default. It just seems like many problems are misattributed to undefined behavior but are actually due to systemic issues in the design of the language.

[thayne]

> Runtime error checks would incur performance penalties

Which is why in rust, there are many runtime checks done in debug builds but not in release builds. (Including checking for wraparound and bounds checks).

The idea being that automated tests should catch the errors, assuming you wrote good tests.

[steveklabnik]

Bounds checks are absolutely done in release builds. The optimizer is more likely to be able to remove ones that are irrelevant, but the checks are not turned off.