mat2: const nml::mat2& operator[](size_t index) const

Return a const reference to x if index is 0 or a const reference to y if index is 1, else, throw an exception.

Example

#include "include/mat2.h"
#include <iostream>

int main() {
        nml::mat2 m(1.0f, 2.0f, 3.0f, 4.0f);
        nml::vec2 a = m[0];
        float b = m[1][0];
        float c = m[1][1];
        std::cout << nml::to_string(a) << ", " << b << ", " << c << std::endl;
        nml::vec2 d = m[2]; // Error

        return 0;
}

Result:

[1.000000, 2.000000], 3, 4
terminate called after throwing an instance of 'std::out_of_range'
        what():  mat2::operator[]: index is out of range.
Aborted