[boost] object persistence without forced base class

From: HanF (hf_p_at_[hidden])
Date: 2002-04-19 01:45:17

Hi all,

i've some ideas for object persistence. A helper to do this is a type like
"any" called "Variant" :-)

If you trapped by the caption of this message, here are some statements:

* no additional base class for types that should be stored
* no registering nor additional type-info for those objects
* clear type requirements: such as copy-constructable
* object implememts serializing by it's self, default:
   left-/right-shift op's, but configurable with member- or
   function-pointer

The variant is based on wellknown publication about those types. A short
description of my idea for persistency follows (statements about "Variant"):

* no template class
* using of member templates
* has two nested types (in inheritance-relation)
   * nested base class: interface "AbstractType",
      required property: pure virtual clone()-method
   * derived: Type<*wrapped type*>, has a
      static prototype-object of wrapped type -
      each construction of Type<> inserts address
      it's prototype in a unique assoc. container:
      map<RTTI-name, AbstractType*>, map is
      hosted in AbstractType, Type<> is clone()-able
      on wrapped type
   * re-store: lookup the map with firstly fetched
      string (RTTI-name) and let it constructing from
      prototype by clone()

Known problems:

* thread safety (static's), but solveable with boost
* wishes: configurable "Variant" to minimize type requirements
   if features are unused
* persistency doesn't works with wrapped pointer to object,
   only available for "holding by value", but checkable with
   boost
* RTTI-name aren't portable and depends from compiler and/or
   bundled types (i.e. STL-types with additional defaulted template
   arguments)
* all stored objects must be used in persistent programm, means
   in most cases: stream must stored by this programm, cause:
   it must existing a prototype (see above)

_________________________
Greetings from Weimar/Germany
    Hans-Friedrich Pabst,
    r.z.w. cimdata AG,
    pabst_at_[hidden]