[boost] Re: dynamic_any campaign?

From: alnsn_at_[hidden]
Date: 2004-06-25 13:07:44

Dr. Franz Fehringer wrote:
> On http://www.cuj.com/boost/ (Boost Corner) the first article is
> I/O System: dynamic_any campaign by Alexander Nasonov.
> Is dynamic_any really scheduled for inclusion in boost (1.32 say)?
> 
Not really. It's not even scheduled for review yet.

Actually, I'm working on multiple dispatch in the library. This means
that call/call_ex scheme will be replaced with something new. My current
favorite is nested definition class (like spirit::grammar's definition).
Implementation for a function with one anyT argument is easy and done
already (I should think it over, though).
Multi-methods come into play when there are more then one anyT in
function's signature. 

My current vision is based on proposal N1529:

 Draft proposal for adding Multimethods to C++
 Document number: WG21/N1529 = J16/03-0112
 Author: Julian Smith
 http://open-std.org/jtc1/sc22/wg21/docs/papers/2003/n1529.html

// Example is taken from N1529

struct  shape            {...};
struct  square   : shape {...};
struct  triangle : shape {...};

bool    overlap( virtual shape& a, virtual shape& b);
    
bool    overlap( static square&   a, static triangle& b) {...}
bool    overlap( static triangle& a, static square&   b) {...}
bool    overlap( static shape&    a, static square&   b) {...}
bool    overlap( static square&   a, static shape&    b) {...}

I'm trying to be as close to this as possible. Compare:

struct overlap : function<overlap, bool(anyT&, anyT&)>
{
  struct definition
  {
    bool operator()(overload_id<0>, square&   a, triangle& b) const {...}
    bool operator()(overload_id<1>, triangle& a, square&   b) const {...}
    bool operator()(overload_id<2>, shape&    a, square&   b) const {...}
    bool operator()(overload_id<3>, square&   a, shape&    b) const {...}

    definition(overlap const& ) {}

    BOOST_STATIC_CONSTAT(int, max_overload_id = 3);
  };
};

New syntax for virtual arguments isn't required because anyT arguments
imply virtuality. In order to enumerate all arguments' combinations
at compile-time, overload_id<N> is introduced.
I hope to finish it within a couple of months.
-- 
Alexander Nasonov