Alternatives to exceptions for error handling

[Ali Çehreli]

On 11/30/20 1:58 AM, Gregor Mückl wrote:
> On Sunday, 29 November 2020 at 23:20:13 UTC, Roman Kashitsyn wrote:
>> On Sunday, 29 November 2020 at 19:52:27 UTC, Jacob Carlborg wrote:
>>> [..]
>>
>> Sure, it's not always possible to handle errors at the level they 
>> arise, those need to be propagated.
>> On the other hand, most of the time the caller has even less clue on 
>> how to deal with the error: the further you go from the point where 
>> error happened, the less likely it's going to be handled in a 
>> meaningful way.
>>
> 
> What kind of error conditions are you talking about that you consider 
> handleable locally? Do you have concrete examples? I am asking because 
> this is way outside the experiences I have made regarding error handling 
> and I would like to understand your perspective.
> 
> Every serious application that I have ever worked on had to deal with 
> errors in the context of larger operations. There were essentially no 
> locally handleable errors. So every error has to go up a few layers 
> until there is even enough context available for recovery. This happens 
> for example when an change operation triggers a sanity check deep inside 
> a complex data model. The failing check has no notion of whether the 
> larger operation needs to be rolled back or whether this is expected by 
> the controller and there is a fallback strategy.
> 

That is exactly my experience as well.

My programs catch Exception type in main() to report a user friendly 
message. (Error is not caught.) There are a couple of exception to this:

- I catch and ignore errors locally in non-essential operations like 
printing verbose output or collecting timing statistics. (Nobody cares 
if they failed and everybody is mad if they failed.)

- I catch formatting errors to augment the error because a higher level 
may not understand a low level error of "cannot convert 'x' to int".

That's all... Exceptions are the simplest error management. For me, 
their only problem is the performance impact, which I haven't even 
measured. :)

The code is the cleanest with exceptions: enforce() and assert() checks 
guarantee that everything is sane. If not, the operation is aborted.

Ali