Aliasing struct and array the C++ way

Question

This is a C++ followup for another question of mine

In the old days of pre-ISO C, the following code would have surprised nobody:

struct Point {
             


        

Answer 1

Use an constexpr array of pointer-to-member:

#include 

struct Point {
    double x;
    double y;
    double z;
};

double dist(struct Point *p1, struct Point *p2) {
    constexpr double Point::* coords[3] = {&Point::x, &Point::y, &Point::z};

    double d2 = 0;
    for (int i=0; i<3; i++) {
        double d = p1->*coords[i] - p2->*coords[i];
        d2 += d * d;
    }
    return sqrt(d2);
}