Listing 3: A better expression template
// Replaces EtMatrixAdd of Listing 2
template<
typename T, size_t n, size_t m,
typename LeftOp, typename RightOp>
class EtMatrixAdd
{
public:
EtMatrixAdd(const LeftOp& lhs, const RightOp& rhs) :
m_lhs(lhs), m_rhs(rhs) {}
T ElementAt(size_t n, size_t m) const
{ return m_lhs.ElementAt(n, m) + m_rhs.ElementAt(n, m); }
private:
const LeftOp& m_lhs;
const RightOp& m_rhs;
};
// Replaces operator= of Listing 2
template<
typename T, size_t n, size_t m,
typename LeftOp, typename RightOp>
Matrix<T, n, m>& operator=(
Matrix<T, n, m>& lhs,
const EtMatrixAdd<T, n, m, LeftOp, RightOp>& rhs
) {
for(int i=0; i<n; ++i)
for(int j=0; j<m; ++j)
lhs.ElementAt(i,j) = rhs.ElementAt(i,j);
return lhs;
}
// Replaces operator+ of Listing 2
template<typename T, size_t n, size_t m>
inline EtMatrixAdd<T, n, m, Matrix<T, n, m>, Matrix<T, n, m> >
operator+(
const Matrix<T, n, m>& lhs,
const Matrix<T, n, m>& rhs
) {
return
EtMatrixAdd<T, n, m, Matrix<T, n, m>, Matrix<T, n, m> >(
lhs, rhs
);
}
// Second operator+
template<
typename T, size_t n, size_t m,
typename LeftOp, typename RightOp
>
inline EtMatrixAdd<
T, n, m,
EtMatrixAdd<T, n, m, LeftOp, RightOp>,
Matrix<T, n, m> >
operator+(
const EtMatrixAdd<T, n, m, LeftOp, RightOp>& lhs,
const Matrix<T, n, m>& rhs
) {
return
EtMatrixAdd<T, n, m,
EtMatrixAdd<T, n, m, LeftOp, RightOp>,
Matrix<T, n, m> >(lhs, rhs);
}
