Question

I’m trying to make a simple Vector class (math) this way:

template <int D, typename T = float>
class Vector
{
  T m[D];
  // ...
};

Where D is the number of dimensions. If it is two, the vector will store two values of type T.

---

How can I declare the constructor function to take D arguments of type T?

Vector<2> v(1.0f, -6.3f);

How to add a function only if D if a specific number? I wish to add GetX() if D is >= 1, GetY() if D is >= 2 and GetZ() if D is >= 3, but the following code should generate a compile-time error:

Vector<2> v(1.0f, -6.3f);
cout << v.GetZ() << endl;

How to generate a compile-time error if D is < 1?

I’m not following any specific standard, anything will work for me.

Answer 1

I don’t have access to a C++11 compiler but maybe something like this could work?

#include <array>
#include <type_traits>

template <int D, typename T>
class Vector
{
    static_assert(D > 0, "Dimension must be greater than 0");
    std::array<T,D> m;
public:
    template<typename... Args>
    Vector(Args&&... args) : m{T(args)...}
    {
         static_assert(sizeof...(Args) == D, "Invalid number of constructor arguments.");
    }

    T GetX() const { return m[0]; }
    T GetY() const { return m[1]; }
    T GetZ() const { return m[2]; }
};

template <typename T>
class Vector<1, T>
{
    std::array<T,1> m;
public:
    Vector(const T& t0) : m{t0}
    {
    }

    T GetX() const { return m[0]; }
};

template <typename T>
class Vector<2, T>
{
    std::array<T,2> m;
public:
    Vector(const T& t0, const T& t1) : m{t0, t1}
    {
    }

    T GetX() const { return m[0]; }
    T GetY() const { return m[1]; }
};