实现一个模板矩阵类

假设我有以下代码：

int main(){
    class Initializer {
    public:
        double operator()(int i, int j) const {
            return i + j;
        }
    };
    Matrix<2,5> m1;
    Matrix<2,5> m2(7);
    Matrix<1,3> m3(Initializer());
    m1(2,3) = 6;
    m2 += m1;
    Matrix<2,5> m4 = m1 + m2;
    return 0;
}

我应该实现一个通用的矩阵来编译和工作上面的代码。在我目前的实现中，我有以下编译错误，我不确定我的错误在哪里：

template <int R, int C>
class Matrix {
private:
    double matrix[R][C];
public:
    //C'tor
    Matrix(const double& init = 0){
        for (int i = 0; i < R; i++){
            for (int j = 0; j < C; j++){
                matrix[i][j] = init;
            }
        }
    }
    Matrix(const Initializer& init) {
        for (int i = 0; i < R; i++){
            for (int j = 0; j < C; j++){
                matrix[i][j] = init(i,j);
            }
        }
    }
    //Operators
    double& operator()(const int& i, const int& j){
        return matrix[i][j];
    }
    Matrix<R,C>& operator=(const Matrix<R,C>& otherMatrix){
        for (int i = 0; i < R; i++){
            for (int j = 0; j < C; j++){
                matrix[i][j] = otherMatrix.matrix[i][j];
            }
        }
        return *this;
    }
    Matrix<R,C>& operator+=(const Matrix<R,C>& otherMatrix){
        for (int i = 0; i < R; i++){
            for (int j = 0; j < C; j++){
                matrix[i][j] = otherMatrix.matrix[i][j] + matrix[i][j];
            }
        }
        return *this;
    }
    Matrix<R,C> operator+(const Matrix<R,C>& otherMatrix) const {
        Matrix<R,C> newMatrix;
        newMatrix = otherMatrix;
        newMatrix += *this;
        return newMatrix;
    }
};

q3.cpp:68:16: warning: parentheses were disambiguated as a function declaration [-Wvexing-parse]
        Matrix<1,3> m3(Initializer());
                      ^~~~~~~~~~~~~~~
q3.cpp:68:17: note: add a pair of parentheses to declare a variable
        Matrix<1,3> m3(Initializer());
                       ^
                       (            )
1 warning generated.
Doppelganger:ex4_dry estro$ g++ q3.cpp
q3.cpp:68:16: warning: parentheses were disambiguated as a function declaration [-Wvexing-parse]
        Matrix<1,3> m3(Initializer());
                      ^~~~~~~~~~~~~~~
q3.cpp:68:17: note: add a pair of parentheses to declare a variable
        Matrix<1,3> m3(Initializer());
                       ^
                       (            )
1 warning generated.