Re: templates and friends

When making a general matrix class I came across the following
situation that I don't have an explanation for. For some friend
functions I have to declare them in advance while other works anyway.
Could anyone care to explain why I have to do it in this way?

Best regards,
Anders

Code follows below

//operator+ here needs to be declared in advanced or I get a compiler
error while operator* works anyway
template<typename T, int ROWS, int COLS>
class Matrix;

template<typename T, int ROWS, int COLS>
Matrix<T, ROWS, COLS> operator+(
const Matrix<T, ROWS, COLS> & lhs,
const Matrix<T, ROWS, COLS> & rhs);