246e2cd1   
   From: marc.glisse@gmail.com   
      
   nroberts  wrote:   
      
   > So I'm trying to make something sort of like a tuple that is accessed   
   > with a placeholder variable using variadic templates.  I keep getting   
   > an error I do not expect:   
   >   
   >   
   > #include    
   >   
   > template < int I > struct arg {};   
   > template < typename ... Pack> struct thingy;   
   >   
   > template < typename Head, typename ... Tail>   
   > struct thingy : thingy   
   > {   
   >    Head val;   
   >   
   >    thingy(Head && h, Tail&& ... t)   
   >       : thingy(std::forward(t)...), val(h)   
   >     {}   
   >   
   >     template < int I >   
   >     auto get(arg) -> decltype(thingy::get(arg()))   
   >     {   
   >       return thingy::get(arg());   
   >     }   
   >   
   >     Head& get(arg<1>) { return val; }   
   > };   
   > template < > struct thingy<> {};   
      
   This looks a lot like:   
      
   http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51501   
      
   You need to find another way to specify the return type of the   
   function, which shouldn't be hard in this case.   
      
      
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