Question

I, like so many others, am writing a linear algebra library for my personal use. In doing so, I’m trying to learn more about programming with templates in C++. I have a class, which goes something like

template<typename T, size_t N, size_t M = N>
class Matrix
{
    ...
}

Now, there are certain operations that I would like to restrict to square matrices (determinant, for example). But when I try to add:

T Determinant<T,N,N>();

It fails to compile, with the error being “Missing ‘;’ before ‘<‘”. I’ve tried adding another template above the determinant call, without any success. Any advice on how to accomplish this would be very much appreciated.

Answer 1

Unfortunately, you cannot specialize a function for specific template parameters like that, you have to do the whole class. Since you don’t want to re-code the entire thing, you probably want to use inheritance.

//shared code
template<typename T, size_t N, size_t M>
class BaseMatrix
{
    //existing code
};

// non-square general case
template<typename T, size_t N, size_t M=N>
class Matrix : public BaseMatrix<T,N,M>
{
    //forwarding headers
    Matrix (const Matrix<T,N,M>& b) : BaseMatrix<T,N,M>(b) {}
};

//square matrix specialization
template<typename T, size_t N>
class Matrix : public BaseMatrix<T,N,N>
{
    //forwarding headers
    Matrix (const Matrix<T,N,M>& b) : BaseMatrix<T,N,M>(b) {}
    T Determinant();
};