Re: [boost] [review] Exception

From: Tobias Schwinger (tschwinger_at_[hidden])
Date: 2007-10-19 07:10:43

Emil Dotchevski wrote:
>> 2. Cloning of the exception. When I catch exception thrown in a worker
>> thread I create clone of it and throw it in the thread which requested the
>> task to be executed in separate thread. It looks like:
>>
>> struct my_exc : public boost::exception
>> {
>>   virtual my_exc* clone() { return new *this; }
>> };
>>
>> I'd created common abstract subclass because of it, perhaps it would make
>> sense somehow to support the feature.
>>
>> I see the http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2007/n2179.html
>> now but it doesn't help me here and now, I think.
> 
> I believe that cloning exceptions is outside the scope of Boost Exception.

Are you sure?

boost::exception can't be a replacement for (modified, according to the 
paper referenced above) std::exception without at least providing the 
abstract member functions.

Further, putting an exception that supports cloning through 
'enable_error_info' currently gives us an exception that only clones a 
subobject, while it's actually quite inviting to have the most derived 
(, unspecified) exception class implement clone/rethrow stuff, isn't it?

>> 2.  Shouldn't all inheritance of "boost::exception," especially via
>> "enable_error_info," be of the virtual kind?
> 
> This is another thing I didn't pay much attention to in the
> documentation, because deriving boost::exception is the same as
> deriving std::exception.
> 
> As for enable_error_info, I am planning to change it to not inject
> boost::exception as a base if it already is a base. This would allow
> enable_error_info to be used in boost::throw_exception regardless of
> whether a particular exception type derives from boost::exception, or
> not. This nullifies the concerns whether enable_error_info uses
> virtual or non-virtual inheritance.

Sounds like a good plan to me.

BTW. what do you think about making the other (, inherited) exception 
accessible through the interface of boost::exception (that is, using a 
reserved tag and having 'what' call inherited 'what' for formatting)?

Regards,

Tobias Schwinger
- Review Manager -