Neat way how to cyclically iterate 4 enum class values in both directions in C++?

Question

I have:

enum class orientation {
  North,
  East,
  South,
  West
};

I want to rotate its instance left (North => West) and right (West => North).
But I don't want to convert them to numbers, because it harms readability and intention and also jumping from the last number to first and back is strange.

I came up with lots of solutions, but all are kind of lame :(

Answer 1

Since they're in order:

constexpr auto rotate(orientation o, int n) -> orientation {
    // convert to int
    int dir = (int)o;
    // rotate as an int
    dir = (dir + n) % 4;
    // account for negatives
    if (dir < 0) {
        dir += 4;
    }
    // and then convert back
    return orientation{dir};
}

Which you can check:

static_assert(rotate(orientation::North, 1) == orientation::East);
static_assert(rotate(orientation::North, -1) == orientation::West);

I picked the integer to mean "number of 90 degree turns right" but you can adjust as suitable for your actual problem. Or add helper functions like:

constexpr auto rotate_left(orientation o) -> orientation {
    return rotate(o, -1);
}

constexpr auto rotate_right(orientation o) -> orientation {
    return rotate(o, 1);
}