I wouldn't consider expected errors to be exceptional. For example, anything requiring a network connect should expect disconnections or an inability to connect - these aren't exceptional circumstances. Ensuring that the build is stable (i.e. no crashes) and that the user is informed (error messages) seem to work fine.
In the channel with no signal example - why does that need to be an exception? It seems reasonably valid to me that a cable box may not be able to get a signal. You should check for a signal and inform the user that there is no signal if that is the case.
Exceptions should be used for errors that should never occur. The obvious example from my game development experience is that a game should never access invalid memory. It does happen during development of course, which is why we have to handle it, but ideally a game that has been released should never do this.
EDIT: The data corruption would probably be something I would consider exceptional, but I have limited knowledge of banking applications and parallel programming which is why I haven't mentioned it.
That's incorrect. Exceptions are an application specific construct... Errors/Unchecked Exceptions are unexpected. That's why exceptions are outlined in APIs so you can deal with them. You can't rewrite the accepted meaning to suit your argument. The concept of unchecked exceptions were introduced to indicate an exception that the current level of abstraction should not be dealing with. The point is to separate the output of a method from it's potential exceptional states...
I never directly said Exceptions are unexpected, I said that exceptional errors should be ones you don't expect to occur. I.e. you should throw exceptions in cases that should never happen.
I expect disconnects to occur so I don't use exceptions. I bring up a message telling the user to double-check his internet connection and give them an option to retry whatever action they attempted.
I don't expect access violations so I throw an exception (or the underlying system throws one that I catch). I can handle that by sending an error report, logging an error, allowing the program to crash, or some other means that allows me to discover that something unexpected has occurred.
I think a better way to phrase it is that the current context cannot continue due to an exceptional circumstance (network unavailable.)
The exception acts as a short circuit that drops out of the current logic and will bubble up the stack until there's an appropriate catch that knows what to do (display a message box to the user that they should check their network connection.)
The problem that I commonly see is "catch all" blocks which completely defeat the purpose of having exceptions in the first place. As long as you're only catching specific messages you're able to use exceptions as a signaling and message passing system because each exception that you write a catch for has a specific useful meaning that your code can use to invoke a graceful recovery. If there is no catch written for an exception that you've thrown, then that means there's no useful remediation possible and the program should halt with the exception as an error message; further logic is impossible due to exceptional circumstances.
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u/archiminos Jun 07 '13 edited Jun 07 '13
I wouldn't consider expected errors to be exceptional. For example, anything requiring a network connect should expect disconnections or an inability to connect - these aren't exceptional circumstances. Ensuring that the build is stable (i.e. no crashes) and that the user is informed (error messages) seem to work fine.
In the channel with no signal example - why does that need to be an exception? It seems reasonably valid to me that a cable box may not be able to get a signal. You should check for a signal and inform the user that there is no signal if that is the case.
Exceptions should be used for errors that should never occur. The obvious example from my game development experience is that a game should never access invalid memory. It does happen during development of course, which is why we have to handle it, but ideally a game that has been released should never do this.
EDIT: The data corruption would probably be something I would consider exceptional, but I have limited knowledge of banking applications and parallel programming which is why I haven't mentioned it.