template parameter representation

[mop65715]

Consider the source snippet

 
typedef hw_default < volatile unsigned short > hw_default_type;
 
typedef hw_register_struct < volatile unsigned short,
                             some_other_policy < unsigned short >,
                             0x500, 
                             0 > hw_register_struct_type;
 
int main() 
{
  unsigned short aa ( 0 );
  foo < volatile unsigned short, 5, 6 > aa5_6 ( aa );
 
  hw_default_type ab ; 
  foo < hw_default_type, 5, 6 > ab5_6 ( ab );
 
  //hw_register_struct_type ac ; 
  //foo < hw_register_struct_type, 5, 6 > ac5_6 ( ac );
 
}

The code today is not extensible because it's structured around the default - hw_default_type which works for 'most' cases. I'm trying to modify source such that I could use the composite type hw_register_struct_type (commented out in main) and hw_default_type as parameters within the same code base. How could I achieve this?