[phobos] Exception chaining

[Don Clugston]

On 12 January 2011 01:10, Andrei Alexandrescu <andrei at erdani.com> wrote:
> On 1/11/11 4:03 PM, Jonathan M Davis wrote:
>>
>> On Tuesday, January 11, 2011 15:50:52 Andrei Alexandrescu wrote:
>>>
>>> I don't think that's helpful. It complicates the flow a lot because now
>>> understanding how the program acts depends not on the types anymore, but
>>> on what happens dynamically. Makes it more difficult, not easier, to
>>> write robust code.
>>>
>>> If I throw a FileException, I must catch a FileException with
>>> catch(FileException) regardless of what collateral exceptions have
>>> happened.
>>
>> I agree as long as it's other Exceptions that have been thrown. But
>> Errors?
>> Aren't they typically supposed to kill your program?
>>
>> - Jonathan M Davis
>
> I agree that non-Exception Throwables are an out-of-band method of
> communication that deserves special attention.
>
> Don, would it be difficult to make a non-Exception Throwable thrown during
> unwinding essentially come to the top of the foodchain and save everything
> in its tail?

It wouldn't be difficult. The difficult thing would be to make a rule
that's sensible and uncomplicated.
The exception handler receives a list of exception records, some of
which are Errors and some are Exceptions,
and it has to determine if a given Object can catch that list.

The chain of D objects is created only when we know we've caught them,
so it can be constructed in any order.