Re: [Boost-users] Debug data structures using aligned storage

From: Edward Diener (eddielee_at_[hidden])
Date: 2006-06-18 20:18:24

David Abrahams wrote:
> Edward Diener <eddielee_at_[hidden]> writes:
> 
> 
> 
>> Pierre THIERRY wrote:
> 
>>> Le Sat, 17 Jun 2006 18:53:19 -0400, David Abrahams a écrit :
> 
>>>> Usually, in the debugger, you cast the base address of the actual
> 
>>>> storage to a pointer to the type stored, and go from there.
> 
> 
>>> Thanks a lot, it did the trick! In fact, I immediately ran into problems
> 
>>> about namespaces, but I managed to find in recent gdb newsgroups
> 
>>> postings how to do...
> 
> 
>>> So now I can debug my varaints! Maybe that could be valuable if such an
> 
>>> information was in the Boost documentation?
> 
> 
>> What Dave suggested is standard information for anyone using a debugger 
> 
>> in C++. Putting that in the Boost documentation is unnecessary.
> 
> 
> 
> I disagree.  Certainly Pierre's experience belies that statement.
> 
> More generally, variant presents a high-level abstraction, and users
> 
> aren't necessarily expected to have any idea how it works internally.
> 
> For the most part, a naive user with a good debugger can explore his
> 
> program's data structures at will, but unlike almost any other library
> 
> component, variant is a barrier to the type information the debugger
> 
> needs.

Variant isn't the only data structure where the actual type stored is 
not known at compile time and therefore unavailable to the debugger to 
show to the user. You yourself pointed out the others. Every good 
programmer of which I know is cognizant of the technique of casting the 
variable or memory area, from within a debugger, to the actual type so 
that the debugger shows the value. Are you saying it should be up to 
Boost to tell the programmer about this technique ? I am not saying it 
might not be helpful, but I do not think it belongs in the documentation 
as a general rule since the technique is universal to other similar 
situations, and not to just one or two Boost libraries.