[serialization] understanding of track_always serialization trait
Folks , I feel a lack of understanding what actually track_always trait does. I expect that boost does not allow me to save/load twice object with the same address? But it reports BOOST_STATIC_ASSERT even in following case: Question 1 Class A { // serialization support }; BOOST_CLASS_TRACKING (A, track_always) BOOST_CLASS_EXPORT( A) … A* a = new A; oa << a ; assert in oserializer.hpp // if your program traps here, it indicates taht your doing one of the following: // a) serializing an object of a type marked "track_never" through a pointer. // b) saving an non-const object of a type not markd "track_never) // Either of these conditions may be an indicator of an error usage of the // serialization library and should be double checked. See documentation on // object tracking. Qurstion 2 Above code with using of xml_oarchive compliles and works: oa << BOOST_SERIALIZATION_NVP(a); oa << BOOST_SERIALIZATION_NVP(a); I expect that it should raise above BOOST_STATIC_ASSERT because I trying to store the same object twice? Question 3 Also I can't understand how track_always serialization trait works in case of Diamond inheritance Quataion from documentation "In a diamond hesitance structure with a virtual base class, object tracking will prevent redundant save/load invocations" How boost knows that this is virtual base class and prevents redundant save/load invocations? Please help me to find the way to understanding of object tracking trait :) Thank you
"Yan Drugalya" <ydrugalya@gmail.com> wrote in message news:2441427d0712240501w2fca0f4em4bedfdeaf2981e3b@mail.gmail.com... Folks , I feel a lack of understanding what actually track_always trait does. I expect that boost does not allow me to save/load twice object with the same address? *** when tracking is enabled for a given type, the keeps a collection of the addresses of all items saved and uses this to be sure that each item is only stored once. So it will allow the same object to be saved more than once, but after the first time, only an object id is saved. note that tracking is usally on/off by default so normally you don't have to specify it. But it reports BOOST_STATIC_ASSERT even in following case: **** This is a separate (though related issue which is described int eh "rationale" section of the documentation. Question 1 Class A { // serialization support }; BOOST_CLASS_TRACKING (A, track_always) BOOST_CLASS_EXPORT( A) const A* a = new A; // at const here. oa << a ; I expect that it should raise above BOOST_STATIC_ASSERT because I trying to store the same object twice? *** no - its raising the assert because the fact that the object is not a "const" suggests that you might be altering in the course of the serialization which would of course conflict with the concept of tracking which in turn suppress extra copies. Question 3 Also I can't understand how track_always serialization trait works in case of Diamond inheritance Quataion from documentation "In a diamond hesitance structure with a virtual base class, object tracking will prevent redundant save/load invocations" How boost knows that this is virtual base class and prevents redundant save/load invocations? *** It doesn't understand the inhertance structure, it just suppresses redundant saves by keeping a record of what it has saved. Please help me to find the way to understanding of object tracking trait :) Thank you You're welcome. Robert Ramey _______________________________________________ Boost-users mailing list Boost-users@lists.boost.org http://lists.boost.org/mailman/listinfo.cgi/boost-users
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Yan Drugalya