03c4a44d   
   From: daniel.kruegler@googlemail.com   
      
   Am 11.02.2012 10:43, schrieb Vidar Hasfjord:   
   > It would be useful to have the primary template parameters visible in   
   > a specialization. Now you need to restate the provided arguments if   
   > you need them within the specialization, and this is a maintenance   
   > hazard. For example:   
   >   
   >   template   
   >   struct TDispatch;   
   >   
   >   template<>  struct TDispatch<42>   
   >   {   
   >     enum {Id = MessageId}; // Error: MessageId is undefined.   
   >     //enum {Id = 42}; // Works, of course, but error-prone.   
   >   };   
   >   
   >   int main()   
   >   {return TDispatch<42>::Id;}   
   >   
   > Is there a good reason why the parameters are not visible?   
      
   I would find it *very* astonishing and problematic, if renaming   
   the parameter name of a primary template would have impact on a   
   specialization where this parameter would be somehow implied. The   
   specialization TDispatch<42> is a class type, no class template anymore,   
   so why bother about names in a completely unrelated type family?   
      
   Further, this mapping would very much depend on the kind of declaration   
   that the specialization sees, e.g. consider   
      
   // Header 1:   
      
   template   
   struct TDispatch;   
      
   // Header 2:   
      
   template   
   struct TDispatch;   
      
   // Header 3:   
      
   template   
   struct TDispatch;   
      
   All three declarations of the TDispatch template are equivalent. Noe   
   consider   
      
   // Header for specialization   
      
   #include  // I=1, 2, or 3   
      
   const int MessageId = 42;   
      
   template<>  struct TDispatch<42>   
   {   
         enum {Id = MessageId};   
   };   
      
   The meaning of this program would now strongly depend on the form of the   
   declaration of the primary template - this looks extremely dangerous to me.   
      
   As the last example demonstares, there are much easier way to ensure   
   consistency, e.g.   
      
   const int MyMessageId = 42;   
      
   template<>  struct TDispatch   
   {   
         enum {Id = MyMessageId};   
   };   
      
   HTH & Greetings from Bremen,   
      
   Daniel Krügler   
      
      
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