Andrei Alexandrescu on exceptions

Source: C++ and Beyond 2012: Andrei Alexandrescu – Systematic Error Handling in C++

Earlier today on the #go-nuts irc channel:

11:32 < nsf>

11:32 < nsf> Andrei invents multiple return values and defer

I have a great deal of respect for Andrei. I think whenever he speaks, you should listen. In watching this video I was struck by his excellent categorisation of some of the less common arguments for errors over exceptions:

  • The exceptional path is slow (00:10:23). Facebook was using exceptions to signal parsing errors, which turned out to be too slow when dealing with loosely formatted input. Facebook found that using exceptions in this way increased the cost of parsing a file by 50x (00:10:42). No real surprise here, this is also a common pattern in the Java world and clearly the wrong way to do it. Exceptions are for the exceptional.
  • Exceptions require immediate and exclusive attention (00:11:28). To me, this is a killer argument for errors over exceptions. With exceptions, you can be in your normal control flow, or the exceptional control flow, not both. You have to deal with the exception at the point it occurs, even if that exception is truly exceptional. You cannot easily stash the first exception and do some cleanup if that may itself throw an exception.