hash function for point with variable dim

pointhash.cpp

  template<int spacedim>
  struct PointHashFunc
  {
      std::size_t
      operator()(const dealii::Point<spacedim>&p) const
      {
        std::size_t h;
        h = std::hash<double>()(p[0]);
        if (spacedim > 1)
          {
            std::size_t h2 = std::hash<double>()(p[1]);
            h = h ^ (h2 << 1);
          }
        if (spacedim > 2)
          {
            size_t h3 = std::hash<double>()(p[2]);
            h = h ^ h3;
          }
        if (spacedim > 3)
          {
            AssertThrow(false, ExcNotImplemented());
          }
        return h;
      }
  };  // struct PointHashFunc

  template<int spacedim, typename T>
  using PointMap =
  std::unordered_map<dealii::Point<spacedim>, T, PointHashFunc<spacedim> >;

Credits to Jean-Paul Pelteret