Question

I created the following Matrix class:

template <typename T>
class Matrix
{
    static_assert(std::is_arithmetic<T>::value,"");

public:
    Matrix(size_t n_rows, size_t n_cols);
    Matrix(size_t n_rows, size_t n_cols, const T& value);

    void fill(const T& value);
    size_t n_rows() const;
    size_t n_cols() const;

    void print(std::ostream& out) const;

    T& operator()(size_t row_index, size_t col_index);
    T operator()(size_t row_index, size_t col_index) const;
    bool operator==(const Matrix<T>& matrix) const;
    bool operator!=(const Matrix<T>& matrix) const;
    Matrix<T>& operator+=(const Matrix<T>& matrix);
    Matrix<T>& operator-=(const Matrix<T>& matrix);
    Matrix<T> operator+(const Matrix<T>& matrix) const;
    Matrix<T> operator-(const Matrix<T>& matrix) const;
    Matrix<T>& operator*=(const T& value);
    Matrix<T>& operator*=(const Matrix<T>& matrix);
    Matrix<T> operator*(const Matrix<T>& matrix) const;

private:
    size_t rows;
    size_t cols;
    std::vector<T> data;
};

I tried to use a matrix of std::complex:

Matrix<std::complex<double>> m1(3,3);

The problem is that the compilation fails (static_assert fails):

$ make
g++-mp-4.7 -std=c++11   -c -o testMatrix.o testMatrix.cpp
In file included from testMatrix.cpp:1:0:
Matrix.h: In instantiation of 'class Matrix<std::complex<double> >':
testMatrix.cpp:11:33:   required from here
Matrix.h:12:2: error: static assertion failed: 
make: *** [testMatrix.o] Error 1

Why std::complex is not an arithmetic type? I want to enable the utilisation of unsigned int (N), int (Z), double (R), std::complex (C) and maybe some home made class (e.g. a class representing Q)… It is possible to obtain this behave?

EDIT 1: If I remove static_assert the class works normally.

Matrix<std::complex<double>> m1(3,3);
m1.fill(std::complex<double>(1.,1.));
cout << m1 << endl;

Answer 1

The arithmetic in is_arithmetic is a misnomer. Or rather, it’s a C++-nomer. It doesn’t mean the same thing as it means in English. It just means it’s one of the built-in numeric types(int, float, etc…). std::complex is not a built-in, it is a class.

Do you really need that static_assert? Why not just let the user try it with any type? If the type doesn’t support the needed operations, then tough luck.