Re: [boost] Reflection?

Subject: Re: [boost] Reflection?
From: Jean-Louis Leroy (jl_at_[hidden])
Date: 2008-11-03 18:17:49

Jeremy Pack wrote:
> Jean-Louis,
> Boost.Reflection handles multiple and virtual inheritance fine.

Does the version from 
http://boost-extension.blogspot.com/2008/07/latest-release-downloadable.html 
contain support for inheritance already?

My primary interest is not in reflection per se, for me it's just a tool 
upon which one can build generic object-processing tools like dumping 
objects to text descriptions or XML or implementing object-relational 
mapping.

Once we have reflection, we need a way to deal with fields in a generic 
manner, whatever their type: int, vector<int>, vector< vector<int> > 
etc. One solution is to reflect the structure of the field's type as 
well: make the field class contain a pointer to a polymorphic type 
object, from which one derives int_type, a vector_type - which contains 
in turn a pointer to the element's type - etc. Pattern freaks will call 
it a composite ;-)

The next step is multimethods. Once we have them we can write code like 
this:

   // using BS's proposed syntax in D&E
   void process_type(virtual type&, virtual processor&, void*);

   void process(instance i, processor& p)
     for each field (i)
       process_type(*field->type, p, field->address(i))

   class text_dumper : public processor { ... };

   void process_type(virtual int_type& t,
     virtual text_processor& p, char* pv) {
     p << *reinterpret_cast<int*>(pv);
   }

   void process_type(virtual vector_type& t,
     virtual text_processor& p, char* pv) {
     p.indent();
     char *iter = t.begin(pv), last = t.end(pv);
     while (iter != last) {
       process_type(t.element_type, p, iter);
       t.forward(iter);
     }
     p.outdent();
   }

What do you think of the idea?

Jean-Louis