21    using size_type = coordinate_type;
 
   23    using const_iterator = 
element const *;
 
   31        using size_type = coordinate_type;
 
   41        [[nodiscard]] 
element &operator[](size_type row);
 
 
   54        using size_type = coordinate_type;
 
   64        [[nodiscard]] 
element const &operator[](coordinate_type row) 
const;
 
 
   79    [[nodiscard]] 
extent size() 
const;
 
   85    void resize(
extent const &size);
 
   95    [[nodiscard]] const_iterator begin() 
const;
 
  105    [[nodiscard]] const_iterator end() 
const;
 
  110    [[nodiscard]] 
column_proxy operator[](coordinate_type column);
 
  121    [[nodiscard]] 
element &get_element(
 
  122        coordinate_type column, coordinate_type row);
 
  127    [[nodiscard]] 
element const &get_element(
 
  128        coordinate_type column, coordinate_type row) 
const;
 
  130    std::vector<element> grid_;