The Right Approach to Exceptions

[foobar]

On Tuesday, 21 February 2012 at 16:15:17 UTC, Juan Manuel Cabo 
wrote:
>> FileNotFoundException is the super class of the others so the 
>> first catch clause is enough. in fact, the others will
>> never be called if listed in the above order.
>
> Nice! I missed that. But what if you want to add ErrorCode and 
> Rainbows?
> And with your approach, one has to test for type and downcast, 
> or
> otherwise have multiple catch blocks (I don't want to miss plain
> FileNotFoundExceptions). So it's square one.
>
> With Variant[string] (or something equivalent, nothing better 
> comes to mind)
> one does:
>
>
>     try {
>         ...
>     } catch (FileNotFoundException ex) {
>          if (ex.hasInfo(MyNameConstant)) {
>              ... use that ...
>          }
>          ... common handling ...
>     }
>
>
> --jm

Regarding the downcast - you still perform a check in the code 
above! You gained nothing by replacing a type check with a check 
on a hash.

Regarding composition of several traits - even that simple 
snippet is enough:
throw new 
WithRainbows!withErrorCode!withFoobar!FileNotFoundException(...);

That's without further design which could probably improve this 
further.