Re: Structured exception information (task, ANEX E)

[Martin Krischik <krischik@users.sourceforge.net>]

Robert A Duff schrieb:
> Martin Krischik <krischik@users.sourceforge.net> writes:
> 
>> Maciej Sobczak schrieb:
>>
>>> Yes, I'm asking for "throwing objects", in the C++ parlance.
>>> How to do this in Ada?
>>> If I cannot - how to solve this design problem?
>> I believe this was skipped in Ada because of ANEX E and task types.
> 
> I don't see any problems there.
> 
>> ...You
>> must understand that Ada exceptions quite often propagated across thread
>> borders and sometimes - if ANEX E is implemented - over a network
>> connections to another computer.
>>
>> I do not say this is impossible but it could be quite expensive
>> performance wise.
> 
> Efficiency is irrelevant to language design.  You should never leave a
> feature out merely because it's slow.  What matters is distributed
> overhead, and I see none here.  Yes, if an exception propagates across a
> network, you have to ship all the data across the network.  The
> programmer controls how much data that is, so it's not a problem.
> Besides, shipping a String is no more efficient than shipping properly
> typed data.

Realy? How about access types? C++ allows access types inside exceptions.

> Many other languages have solved this problem (even in the presence of
> threads and distributed systems).

A Weblogic Server just converts the exception into ...UserException or 
...SystemException and then adds the old exception name as string. Any 
"structured exception information" beeing stripped before propagation.

What a great solution.

> The 200-character limit was a mistake, by the way.  It was based on
> fictitious implementation difficulties.  Ada already has functions
> that return results whose size is not known at the call site (e.g.
> "return String").  The same memory-management techniques would apply to
> arbitrary-sized exception occurrences.

And it is optional - a implementation is free to do it better.

Martin