Re: [boost] [Interest] Value Dispatch

Subject: Re: [boost] [Interest] Value Dispatch
From: Larry Evans (cppljevans_at_[hidden])
Date: 2012-08-15 14:06:49

On 08/15/12 08:49, *smgreened_at_[hidden] wrote:
> Hi all,
> 
> This might be old hat to verteran boosters but I found it nifty.  Maybe
> it could make a small addition to Boost.
> 
> Inspired by Sean Parent's C++Now! talk and the various articles on
> cpp-next, I've been playing around with value semantics and C++11.
> 
> I found an interesting use of pack expansion at stackoverflow and
> expanded on it in a local project to convert from a traditional
> inheritance/virtual function model to a more value-centered approach.
> 
> It turns out that with pack expansion one can implement "virtual
> functions" without needing inheritance or pointer/reference semantics.
> One can consider a vrtual function as "just" a compiler-generated switch
> statement.  With that in mind, here's an example:
> 
> -----------
[snip]
> class vehicle {
> public:
>   enum kind {
>     Car,
>     Bus,
>     Boat,
>     Train,
>     Airplane
>   };
> 
>   typedef kind_tuple<vehicle,
>                      kind::Car, kind::Bus, kind::Boat, kind::Train,
>                      kind::Airplane> kinds;
> 
> private:
[snip]
>   kind the_kind;
> 
> public:
>   vehicle(kind k) : the_kind(k) {}
[snip]
> 
> };
[snip]

Could you not use boost::variant, where the variant which function would
return the tag, which is what the above vehicle::the_kind is,
in essence:

------------
#include <boost/variant.hpp>

  enum kind {
    Car,
    Bus,
    Boat,
    Train,
    Airplane
  };

  template
  < kind Kind
  >
class vehicle_kind
{
};
    typedef
  boost::variant
  < vehicle_kind<Car>
  , vehicle_kind<Bus>
  , vehicle_kind<Boat>
  , vehicle_kind<Train>
  , vehicle_kind<Airplane>
  >
vehicle
;
------------
Then couldn't boost::variant library's static_visitor's do the
dispatching?

-regards,
Larry