Why exceptions for error handling is so important

[Tobias Müller via Digitalmars-d]

Walter Bright <newshound2 at digitalmars.com> wrote:
> On 1/11/2015 5:06 AM, Dicebot wrote:
>> What is your opinion of approach advertised by various functional languages and
>> now also Rust? Where you return error code packed with actual data and can't
>> access data without visiting error code too, compiler simply won't allow it.
> 
> It's a great question. I have a lot of experience with error codes, and
> with exceptions. I have zero with the packed scheme, though that doesn't
> stop me from having an opinion :-)
> 
> Perhaps I misunderstand, but given A calls B calls C,
> 
>    A => B => C
> 
> and C detects an error, and A knows what to do with the error. B then
> becomes burdened with checking for the error, invoking some sort of
> cleanup code, and then propagating it.
> 
> Wouldn't this be uglifying B's source code?
> 
> With exceptions, C throws, A catches, and B's cleanup happens automatically.
> 
> This matters very much for pipeline style programming (i.e. ranges and algorithms).

- Error codes are automatically ignored
- Exceptions are automatically propagated

IMO both are not ideal and lead to sloppy programming.
Ignoring errors is of course worse than aborting where you could have
handled the error.

Rust-style "packed" errors are nice because you are forced to think about
the correct handling.