Re: [Boost-users] [serialization]Multiplydefinedsymbol:guid_initializer

Subject: Re: [Boost-users] [serialization]Multiplydefinedsymbol:guid_initializer
From: Robert Dailey (rcdailey_at_[hidden])
Date: 2009-04-03 16:30:50

On Fri, Apr 3, 2009 at 4:07 PM, Robert Ramey <ramey_at_[hidden]> wrote:

>  **** at this point, the serialization library doesn't necessary doesn't
> know anything about derived. (I'm assuming derived is polymorphic.)
> Depending on what is compiled into the library and waht is inline, there may
> or may not be a problem at link time
>
>
Sorry I feel like we're going in circles about this. Let me explain in
detail how I see what is happening.

Because I'm calling functions off of "base" polymophically from my
executable using the LIB in question, it *cannot* ignore the two classes
"base" and "derived", because I'm actually using the code. The polymorphic
behavior of the function call "base->DoStuff()" touches the implementations
of that function in "base::DoStuff()" and "derived::DoStuff()".

So it isn't the classes themselves being ignored, it has to be something
else. When I call "BOOST_CLASS_EXPORT( derived )", it creates a
specialization of the class "init_guid<>". Right below that, the static
variable inside the "init_guid" struct is statically initialized with some
value from a singleton. This class *cannot* be going away, because the act
of calling a member function off of "derived" (e.g. derived::DoStuff() )
causes that translation unit to be visited, thus causing that static member
to be initialized.

So it seems that given the circumstances, nothing in this translation unit
is going away. Because I am calling a member function off of my "derived"
instance before I serialize it out, the translation unit is being "visited"
and that alone is all that the "derived" class needs.

However, the "base" class has no implementation for "DoStuff", it is pure
virtual. This means the "base" translation unit is not being visited. Is
this the problem? This might be the reason for the "unregistered void cast"
error. Am I on the right track about all of this?

You mentioned a "force_export" header of some sort, but I'm not sure where
you are going with this. As far as I know, this is undocumented behavior in
Boost.Serialization. If someone wouldn't mind providing me a detailed and
functional example of how to use this "force_export" concept, I would
appreciate it. I also do not wish to use archive.register_type<>, because
this requires doing this for every archive I am using. If I add a new
derived type, I'll have to go back and change this. This violates the
open/close principle.

This whole thing is pretty confusing, so I hope you'll bear with me while I
try to understand this.