Template specialization no matching constructor

Question

I am creating a templated vector class that is roughly done in the following way:

// Main class
template <typename T, int DIMS>
class Vector
{
    // Default constructor
    Vector();
    // Data constructor
    Vector(const T data[DIMS]);

    // Other functions, variables, operators
};

// 3d specialization
template <typename T>
class Vector<T, 3>
{
    // Cross product for 3d vectors -- only thing in specialization
    static Vector<T, 3> cross(const Vector<T, 3> a, const Vector<T, 3> b);
};

For the main template, I have a default constructor as well as a constructor specifying the elements. When I try to compile using the constructor with the elements, I get the error no matching constructor for initialization of 'Vec3f' (aka 'Vector<float, 3>') .

Everything similar question that I have looked at indicates that the constructors should automatically work with templated classes, so I'm not sure what is going on here. I previously had constructor errors with classes that didn't have a template specialization and it listed that the other constructor was not viable, which makes me think that the constructor isn't being copied to the templated class for some reason.

Answer 1

Partial and explicit specializations do not inherit anything from the primary template; they are completely unrelated. In your code, a Vector<T, 3> is a completely empty class except for the static member function.

There are ways to reduce code duplication when a partial/explicit specialization share code with the primary template (for instance, by inheriting from a base class template that implements the shared functionality), but in this case I see no reason to write a partial specialization in the first place. Just make cross a free function template:

template <typename T, int DIMS>
class Vector
{
    // Default constructor
    Vector();
    // Data constructor
    Vector(const T data[DIMS]);

    // Other functions, variables, operators
};

template<typename T>
Vector<T, 3> cross(const Vector<T, 3> a, const Vector<T, 3> b);

As a side note, Vector(const T data[DIMS]); may not do what you think it does - it is exactly equivalent to Vector(const T *data); .