[boost] Re: mpl::is_sequence< incomplete_type >?

From: Andreas Huber (spam2002_at_[hidden])
Date: 2003-02-05 07:09:28

Aleksey,

> It might be possible to fix it, but it will require some work. Let
> me know if it's important for you, and I'll move it up in my TODO list.

Well, it is not that important since mpl::is_sequence<> is only used to
provide some syntactic sugar. I could just as well tell my users that they
always have to specify an mpl::list containing a single type instead of a
type under MSVC...

Thanks,

Andreas

P.S. While making my first serious steps with mpl yesterday, I ran into some
weird errors while trying to compile the following with MSVC 7.0. Could this
also be a limitation of my platform? Am I using some functions that are a
problem for MSVC, or am I just missing something?

#include <boost/mpl/placeholder.hpp>
#include <boost/mpl/apply.hpp>
#include <boost/mpl/list.hpp>
#include <boost/mpl/transform.hpp>

template< class Event >
class event_handler
{
  protected:
    event_handler() {}
    ~event_handler() {}

  private:
    virtual bool handle_event( const Event & theEvent ) = 0;
};

template< class Derived, class Event, class Destination >
class transition_handler : public event_handler< Event >
{
  private:
    virtual bool handle_event( const Event & ) { /* */ }
};

template< class Event, class Destination >
struct transition
{
  template< class Derived >
  struct apply
  {
    typedef transition_handler< Derived, Event, Destination > type;
  };
};

class Paused {};
class Running {};
class EvPause {};

// Since I can write this:
typedef boost::mpl::apply< transition< EvPause, Paused >, Running >::type
  handler1;

// I should be able to write the following, or am I missing something?
// Does not compile under MSVC7.0
using namespace boost::mpl::placeholder;
typedef boost::mpl::list< transition< EvPause, Paused > > trans_list;
typedef boost::mpl::transform<
  trans_list, boost::mpl::apply< _, Running > >::type handler_list;
typedef boost::mpl::front< handler_list >::type handler2;

int main()
{
  // this is just to see the type in the debugger
  handler1 * pHandler1 = 0;
  pHandler1;
  handler2 * pHandler2 = 0;
  pHandler2;
  return 0;
}