Templates & Marshaling C++ Function Calls

Listing 1

namespace marshal
{
struct empty_type {};
template <typename T> struct traits // Value types
{
   typedef typename boost::call_traits<T>::const_reference param_type;
   typedef T value_type ;
   enum { in = 1, out = 0, returnable = 1, indirect = 0 };
};
template <> struct traits< void >
{
   typedef void param_type;
   typedef empty_type value_type ;
   enum { in = 0, out = 0, returnable = 1, indirect = 0 };
};
template <typename T> struct traits< out<T&> > // Out-only by reference
{
   typedef out<T&> param_type;
   typedef T value_type ;
   enum { in = 0, out = 1, returnable = 0, indirect = 0 };
};
template <> struct traits< const char * > // C-style string, in-only
{
   typedef const char * param_type;
   typedef c_string<char> value_type; // like std::string but preserves NULL
   static param_type to_arg(value_type & val) { val.m_std_string.c_str();}
   enum { in = 1, out = 0, returnable = 0, indirect = 0 };
};