Re: [Boost-users] [Serialization] Is this example legal usage of the serialization library

Subject: Re: [Boost-users] [Serialization] Is this example legal usage of the serialization library
From: Robert Ramey (ramey_at_[hidden])
Date: 2010-08-26 14:52:12

Elizabeta wrote:
> Hi,
>
> Is it ok to serialize/deserialize in the object I get when
> dereference a pointer ?
>
> void f()
> {
>
>    B* bObj=new B();
>
>     /// save
>     {
>        std::ofstream ofs("C:\\hh.txt");
>         boost::archive::xml_oarchive oa(ofs);
>         oa & make_nvp("bObj",*bObj);
>     }
>     //// Load
>     {
>         std::ifstream ifs("C:\\hh.txt");
>
>         boost::archive::xml_iarchive ia(ifs);
>         ia & make_nvp("bObj",*bObj);
>     }
> }
>
> My second question :
> Is it ok to serialize/deserialize in *this ?
>
> Thanks

I'm going to rephrase the question for my own convenience:

"How is the serialization library intended to be used to do the equivalent 
of: stream << *x ?"

Here is my answer to my own question.

Serializing a data object in a way that most people intend requires that the 
object recreated be "equivalent or substitutable" for the original object. 
When an object includes a pointer, it becomes clear that this is not so 
easy.  There are a number of issues the crop up - including

a) the fact that pointer to class X might really be refering to some derived 
class (virtual inheritance)
b) there might be multiple pointers refering to the same object.
c) same problems for references
d) an the fact that all this might be going on simultaneously.

The usage of ar << *x or ar << *this is an indication that the user is 
likely to "re-implement" some of the serialization library.  This might 
occur because the simple interface of the library suggests that it doesn't 
do much and this is not at all true.  Sooooo if you find yourself wanting to 
do this, step back and think about why you want to do this.  Look into the 
library documentation and examples to see how you might get what you want 
without doing this.  If it's still not clear, it's likely that your 
overlooking something that the library does that is not obvious.  If you 
still feel you have to do this, I've failed in my task.

So the short answer to my phrasing of your question is:

"How is the serialization library intended to be used to do the equivalent 
of: stream << *x ?"

ar << x

This DOES do ar << *x plus everything else that has to be done to make such 
an operation make any sense at all.

Robert Ramey