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I have a bunch of extremely similar matrix classes with only difference in their size.

For example:

class clrMatrix8x8
{
public:
    clrMatrix8x8();
    clrMatrix8x8(const clrMatrix8x8&);
    ~clrMatrix8x8();

    void fill(int);

    static clrMatrix8x8 elemAdd(const clrMatrix8x8&, const clrMatrix8x8&);
    static clrMatrix8x8 elemSubstr(const clrMatrix8x8&, const clrMatrix8x8&);
    static clrMatrix8x8 elemMult(const clrMatrix8x8&, const clrMatrix8x8&);
    static clrMatrix8x8 scalMult(const clrMatrix8x8&, int);
    static clrMatrix8x8 elemDiv(const clrMatrix8x8&, const clrMatrix8x8&);
    static clrMatrix8x8 scalDiv(const clrMatrix8x8&, int);

    int& operator()(size_t, size_t);
    clrMatrix8x8& operator=(const clrMatrix8x8&);
private:
    std::array<std::array<int, 8>, 8> content;
};

There are classes for 16x16, 32x32 and so on. All of them work the same as well as their functions. For clrMatrix8x8, elemAdd function is: 

clrMatrix8x8 clrMatrix8x8::elemAdd(const clrMatrix8x8& first_, const clrMatrix8x8& second_)
{
    clrMatrix8x8 temp(first_);

    for (size_t i = 0; i < temp.content.size(); i++)
    {
        std::transform(temp.content[i].begin(), temp.content[i].end(), second_.content[i].begin(),
            temp.content[i].begin(), std::plus<int>());
    }
    return temp;
}

The only difference between this function and the same function for other matrix is class names.

Since it doesn't feel good to have 5 similar implementations of each function for each class I thought it was possible to make a template function which is friend to all the matrix classes. So, I put template<class T> friend T elemAdd_text(const T&, const T&); in Matrix.h as well as inside 16x16 and 8x8 matrix classes declarations and 

template<class T>
T elemAdd_test(const T& ad, const T& af)
{
    T temp(ad);

    for (size_t i = 0; i < temp.size(); i++)
    {
        std::transform(temp.content[i].begin(), temp.content[i].end(), af.content[i].begin(),
            temp.content[i].begin(), std::plus<int>());
    }
    return temp;
}

in Matrix.cpp to test this out, but when I call this function in main() like this: some8x8matrixVariable = elemAdd_test(other8x8matrix_1, other8x8matrix_2); it gets LNK2001 "unresolved external symbol" error. What am I doing wrong?

I know it would be much easier to just use a vector of vectors, I tested that and array-based matrix worked ~6 times faster, and I need as much performance as possible.

Lenassa
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    Isn't what you're describing just inheritance? You might be digging too deep into c++-specific metaprogramming craziness, this is a problem best solved by basic OOP I think. Make a parent `Matrix` class with each variation as subclasses with a getter for the size. – Klaycon Apr 15 '20 at 18:39
  • Depending on your objective. You could consider how the likes of [Eigen](http://eigen.tuxfamily.org/index.php?title=Main_Page) does it or even just use it for your project. Here is a whole [list of libs](https://stackoverflow.com/questions/1380371/what-are-the-most-widely-used-c-vector-matrix-math-linear-algebra-libraries-a#answer-1380432) – lakeweb Apr 15 '20 at 18:48
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    Instead of using template friend functions, why not make the whole class a template class? – super Apr 15 '20 at 19:04
  • @Klaycon, :/, looks like a solution, I think I'll try that, thanks. – Lenassa Apr 15 '20 at 19:05

0 Answers0