"Peter Dimov" <pdimov@mmltd.net> writes:
Robert Ramey wrote:
David Abrahams wrote:
"Jeff Garland" <jeff@crystalclearsoftware.com> writes:
[...]
The hashing idea is a lot closer to the mark.
Not in my view
I find that very odd, since you later go on to say that this statement:
NOTE: due to a change in the serialization library interface, it is now required that all streamable objects be const prior to writing to the archive.
in inaccurate (which it isn't)
Actually, _I_ said it was inaccurate. You can stream a non-const object just as long as you do it through a const pointer or reference. How weird is that? What other operations do we have in C++ that work on const lvalues and *not* on non-const ones? This is utterly unprecedented and it subverts the fundamental C++ relationship that a non-const object is-a const object.
and explain that:
What is true is that the state of an object should not be changed durring the process of serialization. That is the statement made by save(Archive &ar, const T & t).
The hash check does exactly that, verify that the state of the object hasn't changed.
Exactly, and the const check does not check for that at all. If you extend the logic used to support the const check, a std::list would have to be const in order to call .sort() on it. That's right: it's an error for the comparison operator used to change any of the list's elements in a way that would affect the sort, just like it's an error for any serialization operator to change the objects being serialized in a way that would affect serialization. Can you imagine a sort() member function being const?
Anyway; have you considered making the default tracking level to only track pointer saves but not value saves? This would instantly marginalize the problem.
Yeah, that was another option I was going to mention, but I didn't want to further confuse things.
Mixing object saves and pointer saves is fairly unreliable since it's order dependent (and will create problems later on if the object is versioned), but if one wants to use the library in such a way, the option to enable full tracking would still be there (and get the full const treatment).
-- Dave Abrahams Boost Consulting www.boost-consulting.com