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From: martin.ecker_at_[hidden]
Date: 2005-08-29 07:33:50


I just ran into a nasty thing with Boost.Serialization. While
restructuring some of our base libraries to get rid of unnecessary
headers and reduce header dependencies in general, I suddenly got a
hard-to-track-down #error in basic_archive.hpp saying that I need to
include archive headers before other serialization headers. I remember
a discussion on this list about this subject in the past. I quickly
skimmed through the thread and can only make the same plea as others
have made in that thread:

Please, please, please get rid of this header order dependency. In
larger projects such header order dependencies are incredibly hard
to get right. I also don't see why I shouldn't be able to do the

// A.hpp:

#include <boost/serialization/access.hpp>
#include <boost/serialization/nvp.hpp>

class A
        A(float value)
                : data(value)

        friend class boost::serialization::access;
        template <typename ArchiveT>
        void serialize(ArchiveT& archive, const unsigned int version)
                archive << BOOST_SERIALIZATION_NVP(data);
        float data;

// UsingA.cpp:

#include "A.hpp" // include first to make sure it includes whatever
it needs
#include <boost/archive/polymorphic_binary_oarchive.hpp>


This technique is often used to make sure that headers can be
translated "on their own", i.e. that they include everything they

Another example that demonstrates how hard it can be to get the header
order right:

// B.hpp:

#include <A.hpp>
#include <boost/archive/polymorphic_oarchive.hpp>
// ^-- BOOM! A.hpp includes non-archive serialization headers

class B
        void Save(boost::archive::polymorphic_oarchive& archive) const;

        A a;

Of course I can swap the two includes, but why should I care that
A.hpp includes serialization headers. Also note that this is a
contrived example. It could be that not A.hpp is the culprit, but any
other header included by A.hpp might include serialization headers.
This makes it very hard to find the correct header order. Also,
assuming A.hpp comes from another library that I have not written. Why
should I know about its implementation details. Why should I have to
care in what order I need to include headers from another library.

So again, please, whatever the cause for introducing this header order
dependency is, get rid of it. It wasn't there in Boost.Serialization
1.32.0 and it shouldn't be in 1.33.0 either.

Best Regards,

TAB Austria
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Phone: +43 7229 78040-218
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E-mail: martin.ecker_at_[hidden]

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