"Peter Dimov" <pdimov@mmltd.net> writes:
What if the number n is infinite (e.g. all possible structs consisting only of fundamental types), which is what Robert calls "bitwise serializable"?
Structs aren't bitwise serializable in general because of padding/packing/alignment. Archives that do not have a documented external format and just fwrite whatever happens to be in memory at the time aren't really archives, they are a very specific subset with limited uses (interprocess communication on the same machine, the same compiler and the same version) that should not shape the design.
If Stepanov had used that philosophy we wouldn't have algorithms specialized for random access iterators. Containers with random access are "a very specific subset" with, arguably, "limited uses" (don't forget that the original Lisp guys thought it would be better if everything were made up of cons cells). The ability to specialize generic algorithms to take advantage of special properties of "specific" datatypes is fundamental to Generic Programming. In fact, every example we can think of so far where optimized array serialization is useful is just such a "specific" archive.
("Archive" implies persistency, and relying on a specific memory layout is not a way to achieve it.)
I think Robert's statement "Here, we use the term "serialization" to mean the reversible deconstruction of an arbitrary set of C++ data structures to a sequence of bytes. Such a system can be used to reconstitute an equivalent structure in another program context. Depending on the context, this might used implement object persistence, remote parameter passing or other facility. In this system we use the term "archive" to refer to a specific rendering of this stream of bytes. This could be a file of binary data, text data, XML, or some other created by the user of this library. " defines the intention of the library and if "archive" implies persistency to you it was perhaps an unfortunate naming choice, but I don't think that should be used to make arguments about the design that contradict his intention.
If you have such an archive, you can add an overload SFINAE'd on is_bitwise_serializable
Robert wants portability to vc6, which doesn't support SFINAE. I doubt he'd want to accept a change that, to be practically taken advantage of, would require users to apply SFINAE. -- Dave Abrahams Boost Consulting www.boost-consulting.com