Why I Prefer Exceptions to Error Values
Exceptions are often a better way to handle errors than returning them as values. We argue that traditional exceptions provide better user and developer experience, and show that they even result in faster execution.
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My anecdotal experience is that Rust code, for example, has more calls to unwrap than I’d like. The problem here is that simply unwrapping results will crash the program on errors that could have been a user-visible error message with exceptions.
unwrap() is explicitly not handling the error in a Result type. If you must do this, then at least use except(), to unwrap the code but with an error message if program crashes. Its the equivalent of having Exceptions and then not handling that exception. Therefore your critique is not valid here.
One problem with Exceptions is, you never know what code your function or library calls that can produce an exception. It's not encoded in the type system or signature of the function. So you need to pray and try catch all possible exceptions (I look at this from Pythons perspective), if you don't want a Catch..All, which then you wouldn't know what error this actually is. And you still don't know where this error came from or happened in the code, how deep in the function call chain? Instead Errors as Values means its encoded in type system and you can directly see what errors the function can cause and (in Rusts case) you must handle the error, otherwise program won't compile. You don't need to handle anything else in this context. Compiler ensures that all possible errors are handled (again within context of our discussion). Vast improvement!
you never know what code your function or library calls that can produce an exception
As far as I remember, there were several attempts at introducing exceptions into type system, and all have failed to a various degree. C++ abandoned the idea completely, Java has a half-assed exception signature where you can always throw an unexpected exception if it's runtime exception, mist likely there were other cases, too.
So yeah, exception as part of explicit function signature is a vast improvement, I completely agree
So yeah, exception as part of explicit function signature is a vast improvement, I completely agree
Hmm, I'm not sure if you are being sarcastic. In my reply I didn't meant encoding Exceptions into Type system. Is this a type and you probably meant "Error Types as part of" instead "exception as part of"?
Honestly I don't know how Exceptions as part of type system would even look like. Because each function call in a chain would need to have all information from previous function call, otherwise that information gets lost to the next caller. The problem is the hierarchy of function and method calls. Somewhere some objects and functions can be edited to Throw a new Exception, that is not handled through the entire chain. And for the higher function caller, there is 0% way of knowing that (through code, besides documentation off course).
Yeah, I shaped my words poorly. What I meant is that errors are sort of equivalent to exceptions, but errors are first class citizens of type system, and this is an improvement over exceptions being kind of independent of type
Ah it was intentional and now I see how it was meant. It makes perfectly sense, it was just not clear before. :-) Human language and interpreter is not as precise like programming language.^^