When #undef DUMMY_ARG1, the following code:

--{--cut here--
//#define DUMMY_ARG1

   template
   < typename Arg0_0
   >
   struct
level_0
{
       template
       < typename Arg1_0
     #ifdef DUMMY_ARG1
       , typename Arg1_1=void
     #endif
       >
       struct
     level_1
     {
     };
       template
       < //typename Arg1_0
     #ifdef DUMMY_ARG1
         typename Arg1_1
     #endif
       >
       struct
     level_1
       < int //specialization on Arg1_0
     #ifdef DUMMY_ARG1
       , Arg1_1
     #endif
       >
     {
     };
};

--}--cut here--

when compiled with gcc4.5, produces errors:
--{--cut here--
x.cpp:24:7: error: explicit specialization in non-namespace scope
'struct level_0<Arg0_0>'
x.cpp:26:5: error: template parameters not used in partial
specialization:
x.cpp:26:5: error:         'Arg0_0'
--}--cut here--

However, when #define DUMMY_ARG1, no errors occur.
It seems a waste to have to provide a dummy template argument
to workaround this limitation.

What's the rationale for this limitation on nested class template
specialization?

-regards,
Larry

--
[ comp.std.c++ is moderated.  To submit articles, try just posting with ]
[ your news-reader.  If that fails, use mailto:std-c++@netlab.cs.rpi.edu]
[              --- Please see the FAQ before posting. ---               ]
[ FAQ: http://www.comeaucomputing.com/csc/faq.html                      ]