Re: [Boost-users] [serialization] Can one serialize classes based offthe curiously-recursive template pattern (or anynon-polymorphic base)? (was: Re: Visual Studio 2008 + Boost1.35:runtime casting not working)

From: Robert Ramey (ramey_at_[hidden])
Date: 2008-07-16 04:13:14

Daryle Walker wrote:

> How strict is the requirement that a base class has to be
> polymorphically connected to the derived class?

It's a fundamental requirement.  Without a vtable it just
won't work.

>  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.

no problem.  virtual dispatch only costs you time if you use it.
It does cost a little space for the vtable - but with only one
virtual function that shouldn't be too much.

There are other options to look at.  maybe you don't want to
serialize through a base class pointer.  Perhaps serializing
something like boost::variant - (in the library) might be
a better choice.

your example below doesn't need to serialize through a pointer
to the base class.  Just use the BASE_OBJECT macro or
type to invoke the base class serializaton.

Robert Ramey

>
> //==============================================
> 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 & BASE_OBJECT(counter_base<my_class>, this);  // I forget the exact 
syntax
> ar & factor;
> }
> };
> //==============================================