Re: [Boost-users] Serialization: docs regarding abstract base class

From: Hugh Hoover (hugh_at_[hidden])
Date: 2006-03-01 19:47:06

On Mar 1, 2006, at 00:59, RIVASSEAU Jean Noel wrote:

> I quote the Boost serialization docs:
>
>
>
> When serializing an object through a pointer to its base class and  
> that base class is abstract (i.e. has at least one virtual function  
> assigned a value of 0), A compile error will be emitted. This is  
> addressable in one over several ways:
>
> *	remove the =0 in the base classes so that the base class is no  
> longer abstract.
> *	implement is_abstract for your compiler. (code written according  
> to the C++ standard is included with this library. But it is known  
> to fail on several compilers.
> *	use the macro BOOST_IS_ABSTRACT(my_class) to indicate that the  
> class is an abstract base class. This will cause the compiler to  
> avoid generating code that causes this error.
>
> I still do not understand part 2 of this advice, Robert. Could you  
> explain?

The BOOST_IS_ABSTRACT macro expands into a specialization of the  
is_abstract template (in is_abstract.hpp) for the specified class,  
and returns mpl::bool<true> for the specified type.

I think part 2 is a suggestion that a more general template may be  
written on a per-platform basis that properly returns mpl::bool<true>  
when the class is derived from an abstract base class.  It's left as  
an exercise for the reader :)  I'm not up to it right now myself...

> Ps: as already mentioned, part 3 does not change anything for me,  
> and I'd like to avoid the solution of part 1 since I do want the  
> base class to be abstract.

I've found that it doesn't matter if you use BOOST_IS_ABSTRACT on the  
actual abstract base class, but you MUST (currently - 1.33.0) on the  
DERIVED class to get it to work "correctly".

I'd consider this a bug, but I'm not sure of the specification and  
haven't had time to research it.