[phobos] Exception chaining

[Andrei Alexandrescu]

On 1/12/11 11:56 AM, Don Clugston wrote:
> On 12 January 2011 16:01, Sean Kelly<sean at invisibleduck.org>  wrote:
>> Two errors could still cause confusion though.
>
> Yeah. Though how much of a problem is it?
> Catching an Error is a nasty action. A nothrow function is permitted
> to throw an Error because it is non-recoverable, so catching it in
> order to recover is somehow a bit shady. (Should it be legal to catch
> an Error in a @safe function?)

I think @safe means memory-safe so probably it could. Catching Error 
means you continue with broken assumptions about the program, but the 
memory safety guarantees are preserved.

> This whole exception chaining idea is based on the premise that it's
> the first error which is the important one. I do think that applies
> even to Errors; I think it's still better than C++'s replacement
> strategy. Can you think of any other way of doing it?

I agree Error is an out-of-band signal that trumps over the nice chain.

> We could say something like, "catching an Error is not something which
> should be done lightly. In the rare cases where it is necessary, you
> should _always_ check for secondary Errors which may have occurred
> while processing the first one."

I'd even be okay with throwing an Error replaces the whole chain. Error 
is a worst-case scenario in which you're allowed to lose state and 
reduce guarantees.


Andrei