By taking advantage of integer wrapping and a bitwise and, its quite a
simple problem to solve!
Challenge for the reader: add support for binary operations and toString
support.
https://dlang.org/spec/operatoroverloading.html
```d
struct Direction {
private int value;
Direction opUnary(string op:"++")() {
value++;
value &= 7;
return this;
}
Direction opUnary(string op:"--")() {
value--;
value &= 7;
return this;
}
void opOpAssign(string op:"+")(int amount) {
value += amount;
value &= 7;
}
void opOpAssign(string op:"-")(int amount) {
value -= amount;
value &= 7;
}
enum Direction N = Direction(0);
enum Direction NE = Direction(1);
enum Direction E = Direction(2);
enum Direction SE = Direction(3);
enum Direction S = Direction(4);
enum Direction SW = Direction(5);
enum Direction W = Direction(6);
enum Direction NW = Direction(7);
}
unittest {
Direction direction = Direction.N;
direction++;
assert(direction == Direction.NE);
direction+=3;
assert(direction == Direction.S);
direction--;
assert(direction == Direction.SE);
direction-=4;
assert(direction == Direction.NW);
}
```
