C++ template typedef

c++ templates c++11 typedef

Notinlist · May 8, 2010 · Viewed 175.9k times · Source

I have a class

template<size_t N, size_t M>
class Matrix {
    // ....
};

I want to make a typedef which creates a Vector (column vector) which is equivalent to a Matrix with sizes N and 1. Something like that:

typedef Matrix<N,1> Vector<N>;

Which produces compile error. The following creates something similar, but not exactly what I want:

template <size_t N>
class Vector: public Matrix<N,1>
{ };

Is there a solution or a not too expensive workaround / best-practice for it?

Answer

C++11 added alias declarations, which are generalization of typedef, allowing templates:

template <size_t N>
using Vector = Matrix<N, 1>;

The type Vector<3> is equivalent to Matrix<3, 1>.

In C++03, the closest approximation was:

template <size_t N>
struct Vector
{
    typedef Matrix<N, 1> type;
};

Here, the type Vector<3>::type is equivalent to Matrix<3, 1>.