Method operator<

dlib/geometry/rectangle.h:263–274

        }

        inline bool operator< (const dlib::rectangle& b) const
        { 
            if      (left() < b.left()) return true;
            else if (left() > b.left()) return false;
            else if (top() < b.top()) return true;
            else if (top() > b.top()) return false;
            else if (right() < b.right()) return true;
            else if (right() > b.right()) return false;
            else if (bottom() < b.bottom()) return true;
            else if (bottom() > b.bottom()) return false;
            else                    return false;
        }

    private:
        long l;