C ++ partial specialization (function pointers)

Can anyone please tell if below is legal c ++ or not?

template < typename s , s & (*fn) ( s * ) > 
class c {};

      

        
        
        
      

    

// partial specialization

template < typename s , s & (*fn) ( s * ) > 
class c < s*, s* & (*fn)(s**)  {};

      

        
        
        
      

    

Error

g ++ (4.2.4): function call cannot appear in constant expression Error: template argument 2 is not valid

Although it works for explicit specialization

int & func ( int * ) { return 0; }
template <> class c < int , func> class c {};