Boost logo

Boost :

From: Dave Harris (brangdon_at_[hidden])
Date: 2003-10-06 04:17:58

In-Reply-To: <blqvc0$mhl$1_at_[hidden]>
ghost_at_[hidden] (Vladimir Prus) wrote (abridged):
> As Robert noted, you still have to make load_construct a friend of the
> serialized class.

No, you can instead overload it for the serialised class. You can add the
overload without modifying the class. It is a non-intrusive approach.

I seem to say this in every message, yet people don't seem to get it. I
don't know how to say it any clearer. I know you saw the example, because
you comment on it below.

> Eh... you gave the following example:
> template<class Archive>
> void load_construct(Archive & ar, my_class *pt, unsigned int version)
> {
> int a;
> ar >> a;
> new( pt ) my_class( a );
> load( ar, *pt, version );
> }
> It's good, but it presumes that "save" method has written "a" for you to
> load. That's somewhat breaks duality between "save" and "load". Now
> "save" should care about another function "load_construct", which is
> somewhat more complex.

In the current proposal, the pointer version of load:

    template<class Archive ar, class T>
    void load(Archive & ar, T * &t, unsigned int file_version);

is paired with a pointer version of save:

    template<class Archive ar, class T>
    void save(Archive & ar, const T * t, unsigned int file_version);

In the same way, in my suggestion load_construct needs to be paired with a
save_construct (there may be a better name). The library uses
save_construct to save in those situations where it knows it will be using
load_construct to load. A user who overrides ones must also override the

Sorry I didn't mention this before - I thought it was obvious. Every load
function needs a corresponding symmetric save function. Duality is
preserved. Do you see any reason this can't be done?

> FWIW, in my use case it won't work, since I don't have any ctor which
> can be used to reconstruct the class instance given field values.

If there is no constructor, how do you make instances? You understand that
your custom load_construct can follow construction with a normal
serialisation load?

-- Dave Harris, Nottingham, UK

Boost list run by bdawes at, gregod at, cpdaniel at, john at