Re: [boost] [Serliazation] Auto registration/physical coupling(was: Thread-safety again)

From: Robert Ramey (ramey_at_[hidden])
Date: 2007-01-04 17:36:10

Emil Dotchevski wrote:
>> Sorry, I don't think that's an accurate statement of anything.  This
>> is accurate:
>>
>>   In a given translation unit (TU), all combinations of A and T,
>>   where A is an archive registered (in the TU) with
>>   BOOST_SERIALIZATION_REGISTER_ARCHIVE and T is a class exported (in
>>   the TU) with BOOST_CLASS_EXPORT(**) are used to instantiate
>>   polymorphic pointer serialization code.  Period.
>>
>>   The translation unit or some portion of it may later be discarded
>>   if the linker can prove none of its functions or objects are used,
>>   or else its initializers may be skipped.  Separate issue.
>
> Just to clarify, besides the portability issues, I brought up the
> issue of the templates being instantiated by the BOOST_CLASS_EXPORT
> macro because it introduces physical coupling between the classes
> being registered and the serialization library. Perhaps I need to
> clarify what I mean.
>
> //foo.h
>
> class foo;
>
> template <class A>
> void operator<<( A &, foo const & );
>
> class foo
> {
> public:
>  foo();
> private:
>  int m_;
>  template <class A>
>  friend void operator<<( A &, foo const & );
> };
>
> template <class A>
> void operator<<( A & a, foo const & x )
> {
>  a << x.m_;
> }
>
> The above foo.h defines class foo, and also specifies how objects of
> class foo are serialized, yet there is no (physical) coupling between
> foo.h and a serialization library, because foo.h does not include any
> headers. This is a good thing: typically, most of the compilation
> units that #include "foo.h" will not serialize foo objects; the ones
> that do serialize foo objects will know to #include "foo.h" and a
> (compatible) serialization library. Also consider that I can write a
> program that makes use of class foo yet doesn't use/include/link a
> serialization library.
>
> This would not be possible if foo.cpp auto-registers class foo with a
> serialization library.
>
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