Strange C2664 in Visual Studio 2005 C++ release candidate (v8.0.50727.26)

I'm converting a project from VS 6.0 SP5 to VS 2005 rc.  I'm getting this really odd C2664 error.  Unfortunately, the project is very complex and I have not yet been able to reproduce this behavior with a simple example.  I can, however, offer proof  of its strangeness:

   DBString dbx = m_scCal.operator const DBString();
   DBString dby = m_scCal;
   DBString dbz = ( const DBString )m_scCal;

Of the three example statements above, only the first one compiles.  I have no idea how it is that an explicit invocation of a converstion operator via the "." syntax can work, but explicit conversion through the type-cast syntax does not.

The error I get depends on whether or not I attempt an explicit or implicit conversion of the original type.

Note: the typedef "typedef CPVString DBString" exists in the preprocessor input stream for these source files.


An explicit conversion attempt yields:

c:\development\turboese_64\database\schema\objects.cpp(39) : error C2440: 'initializing' : cannot convert from 'const ft_structure_code' to 'CPVString'

Qualification conversion
followed by
Call to user-defined-conversion 'TDBField<managed_type>::operator const DBString(void) const'
with
[
   managed_type=DBFieldString
]
c:\development\turboese_64\database\dbenviron.h(906) : see declaration of 'TDBField<managed_type>::operator const DBString'
with
[
   managed_type=DBFieldString
]
followed by
Exactly the same type
followed by
Call to user-defined-conversion 'TDBField<managed_type>::operator const DBFieldString &(void) const'
with
[
   managed_type=DBFieldString
]
c:\development\turboese_64\database\dbenviron.h(912) : see declaration of 'TDBField<managed_type>::operator const DBFieldString &'
with
[
   managed_type=DBFieldString
]
followed by
Binding to reference

The above error seems particularly strange, given that the diagnostic information it provides seems to show a perfectly acceptable conversion path. Why didn't it use it

I set up the following code fragment in an attempt to reproduce this behavior, but it works perfectly:

typedef char _TCHAR;
typedef const char *LPCTSTR;

class CPVString
{
   public : CPVString ();
              CPVString ( _TCHAR, int );
              CPVString ( LPCTSTR lpch, int nLength );

   public : virtual ~CPVString ();

   public : CPVString ( const CPVString & );
              CPVString ( LPCTSTR );
};

typedef CPVString DBString;

DBString ConvertToDBString()
{
    return ( DBString() );
}

template < class managed_type, int nBindingCount = 4 > class TDBField
{
   public : operator const DBString () const { return ( ConvertToDBString() ); }
};

typedef TDBField< bool > ft_Foo;

class CBar
{
   public : void SomeFunc() const
              {
                  DBString dby = ( const DBString )m_fooData;
              }

   private : ft_Foo m_fooData;
};

The above is extracted directly from my code, although the various class definitions did not originally reside in the same include file and have also been truncated for brevity.