[Boost-users] [serialization] Can one serialize classes based off the curiously-recursive template pattern (or any non-polymorphic base)? (was: Re: Visual Studio 2008 + Boost 1.35:runtime casting not working)

From: Daryle Walker (darylew_at_[hidden])
Date: 2008-07-16 02:43:03

On Jul 14, 2008, at 5:40 PM, Steve Sanders wrote:

> Thank you, that makes my sample work.  These points could be  
> clearer in the docs, I would say.
>
>> From: boost-users-bounces_at_[hidden] [mailto:boost-users- 
>> bounces_at_[hidden]] On Behalf Of Robert Ramey
>> Sent: Monday, July 14, 2008 2:54 PM
>> To: boost-users_at_[hidden]
>> Subject: Re: [Boost-users] [serialization] Visual Studio 2008 +  
>> Boost 1.35:runtime casting not working
>>
>>
>>
>> The base class MUST be polymorphic - that is have at least one  
>> virtual function.
>>
>>
>>
>> AND the the pointer to the base class - not the derived class  
>> should be serialized.
>>
>>

How strict is the requirement that a base class has to be  
polymorphically connected to the derived class?  I have a class that  
derives from a class template that uses the curiously-recurring  
template pattern.  Such base classes are usually without any kind of  
virtual stuff, to allow inlining of parent methods and avoid the hit  
virtual dispatch.

//==============================================
template < class Derived >
class counter_base
{
public:
        void  count()  { ++counter; }
        int   current_count() const  { return counter; }
protected:
        counter_base()  : counter( 0 )  {}
private:
        int  counter;
        friend class boost::serialization::access;
        template < class Archive >
        void  serialize( Archive &ar, unsigned const file_version )
        { ar & counter; }
};

class my_class
        : private counter_base<my_class>
{
        typedef counter_base<my_class>  base_type;
        typedef my_class                self_type;
public:
        explicit  my_class( double factor = 1.0 )  : factor( factor )  {}
        double  next()  { count(); return factor * current_count(); }
private:
        double  factor;
        friend class boost::serialization::access;
        template < class Archive >
        void  serialize( Archive &ar, unsigned const file_version )
        {
                ar & ???;  // what goes here for base_type (or base_type::counter)?
                ar & factor;
        }
};
//==============================================

-- 
Daryle Walker
Mac, Internet, and Video Game Junkie
darylew AT hotmail DOT com