(Pseudo-) Path Dependent types, C++11 style.

pdt.cpp

include <set>
#include <assert.h>

template<typename Unutterable>
struct Board
{
  int length;
  int height;

  struct Coordinate
  {
     int x;
     int y;
     private:
     Coordinate(int x_, int y_) : x(x_), y(y_) {}
     friend class Board;
     public:
     Coordinate() = default;
     Coordinate(const Coordinate&) = default;
     Coordinate(Coordinate&&) = default;

     bool operator==(const Coordinate& o) const { return x == o.x && y == o.y; }
     bool operator <(const Coordinate& o) const { return x < o.x || (x == o.x && y < o.y); }
  };
  std::set<Coordinate> occupied;

  Board(int l, int h) : length(l), height(h) {}
  Coordinate newCoordinate(int x, int y)
  {
     assert(0 <= x && x <= length && 0 <= y && y <= height);
     return Coordinate(x,y);
  }
};

template<typename U>
Board<U> do_make_board(U u, int l, int w)
{
   return Board<U>(l, w);
}

#define make_board(l,w) (do_make_board([](){}, l, w))


int main()
{
  auto b1 = make_board(20, 20);
  auto b2 = make_board(30, 30);
  auto c1 = b1.newCoordinate(15, 15);
  auto c2 = b2.newCoordinate(25,25);
  b1.occupied.insert(c1);

  //b1.occupied.insert(c2);
}