Re: Start of Lua rewrite in C++

[Colin <share-lua@...>]

On Wed, Oct 24, 2007 at 12:38:59PM -0500, James Porter wrote:
> On 10/24/07, Colin <share-lua@think42.com> wrote:
> >
> > - Change Lua to satisfy the exception requirements I mentioned in another
> > mail:
> >   - Report errors from Lua as exceptions
> >   - Allow exceptions to safely "fly through" Lua
> >   which would make integration in C++ projects a heck more easy (that is
> > C++
> >   projects on the level of "Exceptional C++" and "Modern C++ Design").
> 
> This can already be done by redefining LUAI_THROW and LUAI_TRY and making a
> lua_exception class. I needed this feature for a project of my own, and
> managed to patch it into Lua 5.1.2 pretty easily. I agree that compiling Lua
> as C++ isn't enough, but I don't think a rewrite is necessary. If you're
> interested, I could put together a patch file with my changes.

Your patch would be highly welcome, yes! I am curious how you manage "fly 
through" of exceptions without some half-serious changes...

Thanks, Colin


PS: Just thinking about Lua in C++ makes me think of all strange things...

   template< typename T > struct ttraits;

   template<> struct ttraits< void > { static const uint8_t type = 0; }
   template<> struct ttraits< bool > { static const uint8_t type = 1; }

   class tvalue
   {
   public:
      tvalue()
            : m_type( ttraits< void >::type )
      { }

      template< class T > T & get()
      {
         if ( m_type != ttraits< T >::type )
            throw "type mismatch bla bla";
         else if ( sizeof( T ) <= sizeof( m_data ) )
            return * reinterpret_cast< T * >( m_data );
         else
            return * reinterpret_cast< T * >( m_pointer );
      }

      template< class T > void set_small( const T & t )
      {
         m_type = ttraits< T >::type;

         BOOST_STATIC_ASSERT( sizeof( T ) <= sizeof( m_data ) );

         new ( m_data ) T( t );
      }

   private:
      union
      {
         void * m_pointer;
         uint8_t m_data[ 2 * sizeof( void * ) - 1 ];
      };
      uint8_t m_type;
   };