Re: Serialization (Persistence) library draft submiss ion

From: quendezus (quendez_at_[hidden])
Date: 2002-02-28 12:16:54

--- In boost_at_y..., johan.nilsson_at_e... wrote:
> 
> To keep as non-intrusive as possible, it would be possible to 
support
> specialized marshallers to support non-default constructors - 
thereby
> allowing legacy objects to be marshalled, e.g.:
> 
> on reading:
> 
> ... gps_position_marshaller::read(T& ar, ...)
> {
> 	X par1, par2;
> 	ar >> par1 >> par2;
> 	gps_position* pos = new gps_position(par1, par2);
> 	...
> }
> 
> // Johan
> 

The problem is that you can not always express deserialization as an 
existing constructor call. See the code below :

struct C
        {
        A a_;	// An attribute of type A
        B b_;	// An attribute of type B
        C veryHardToComputeValue_;	// An attribute of type C

        C( const A& a, const B& b ) : a_( a ), b_( b )
                {
                // Very long computing
                veryHardToComputeValue_.compute( a, b );
                }
        };

void save( Archive& a, const C& c )
        {
        a << c.a_;
        a << c.b_;
        a << veryHardToComputeValue_;
        }

void load( Archive& a, C& c )
        {
        a >> c.a_;
        a >> c.b_;
        a >> veryHardToComputeValue_;
        }

In that case you do not have any constructor to call and pass 
veryHardToComputeValue as a parameter. Even if you could modify the 
class to add a constructor that would take A&, B& and C&, you could 
have problem to pass the C& parameter because maybe you don't want to 
copy it or deal with allocation of that parameter.

Sylvain