text: #ifndef CONNECTION_HPP_
  #define CONNECTION_HPP_
  
  #include "BoundingBox.hpp"
  
  class Connection {
   public:
    explicit Connection(BoundingBox *const b1, BoundingBox *const b2);
    ~Connection();
  
    double attraction() const { return attraction_; }
    double cost() const { return cost_; }
  
   public:
    double attraction_, cost_;
  
   private:
    friend inline bool operator<(const Connection &e1, const Connection &e2) {
      return e1.cost() < e2.cost();
    }
  };
  
  #endif  // CONNECTION_HPP_