Template with boost::operators extremely verbose and repeating

Question

I got the following ugly code:

template < class _Coeff,
 unsigned _nVars,
 typename _Expo=int,
 template <class, class> class _Map = _Map >
class Polynomial
 : boost::ring_operators< Polynomial<_Coeff,_nVars,_Expo,_Map>
 , boost::addable < Polynomial<_Coeff,_nVars,_Expo,_Map>, _Coeff
 , boost::addable < Polynomial<_Coeff,_nVars,_Expo,_Map>,
 std::pair< std::array<_Expo,_nVars>, _Coeff >
 , boost::subtractable < Polynomial<_Coeff,_nVars,_Expo,_Map>, _Coeff
 , boost::subtractable < Polynomial<_Coeff,_nVars,_Expo,_Map>,
 std::pair< std::array<_Expo,_nVars>, _Coeff >
 , boost::multipliable < Polynomial<_Coeff,_nVars,_Expo,_Map>, _Coeff
 , boost::multipliable < Polynomial<_Coeff,_nVars,_Expo,_Map>,
 std::pair< std::array<_Expo,_nVars>,_Coeff >
 > > > > > > > {

In particular, I hate to repeat Polynomial<_Coeff,_nVars,_Expo,_Map>. Is there a way to improve this syntax without using the preprocessor ? I can't manage to get any help from the using keyword here.

Just for the infos: I'm writing multivariate polynomials where _Coeff is the class of the coefficients and the terms X1^4x2^4 are represented as std::array<_Expo,_nVars>.

Answer 1

Easy, with default template arguments:

template < class _Coeff,
 unsigned _nVars,
 typename _Expo=int,
 template <class, class> class _Map = _Map
 typename Poly = Polynomial<_Coeff,_nVars,_Expo,_Map>,
 typename Pair = std::pair< std::array<_Expo,_nVars>, _Coeff > >
class Polynomial
 : boost::ring_operators< Poly
 , boost::addable < Poly, _Coeff
 , boost::addable < Poly, Pair
 , boost::subtractable < Poly, _Coeff
 , boost::subtractable < Poly, Pair
 , boost::multipliable < Poly, _Coeff
 , boost::multipliable < Poly, Pair
 > > > > > > > {

• hivert: I don't like it that much because it expose non-sensical parameter to the user. But then I can re-hide them by a front-end using template... OK !
• iavr: @hivert Indeed I, would also name this Polynomial_Impl or something, then add a template alias to this. The remaining default template arguments would go to the interface, not the implementation.
• Manu343726: Add a std::enable_if at the end to check the user did not change those extra parameters