Data references

The following is the data reference equivalent to the example code using an object. It's shorter but less clear (IMHO).

TYPES:
  BEGIN OF t_place,
    place TYPE char30,
  END OF t_place,
  t_place_tab TYPE TABLE OF t_place,
  BEGIN OF t_city,
    city_name TYPE char20,
    places_ref TYPE REF TO data,
  END OF t_city.

FIELD-SYMBOLS:
  <ref> TYPE t_place_tab.

DATA:
  gt_city TYPE HASHED TABLE OF t_city WITH UNIQUE KEY city_name,
  gs_city TYPE t_city,
  gs_place TYPE t_place.

START-OF-SELECTION.
  gs_city-city_name = 'Porto'.
  CREATE DATA gs_city-places_ref TYPE t_place_tab.
  ASSIGN gs_city-places_ref->* TO <ref>.
  gs_place-place = 'Torre dos Clerigos'.
  APPEND gs_place TO <ref>.
  gs_place-place = 'Casa da Musica'.
  APPEND gs_place TO <ref>.
  gs_place-place = 'Serralves'.
  APPEND gs_place TO <ref>.

  INSERT gs_city INTO TABLE gt_city.

  gs_city-city_name = 'New York'.
  CREATE DATA gs_city-places_ref TYPE t_place_tab.
  ASSIGN gs_city-places_ref->* TO <ref>.
  gs_place-place = 'Empire State Building'.
  APPEND gs_place TO <ref>.
  gs_place-place = 'Central Park'.
  APPEND gs_place TO <ref>.

  INSERT gs_city INTO TABLE gt_city.

  READ TABLE gt_city INTO gs_city WITH KEY city_name = 'Porto'.
  IF sy-subrc = 0.
    ASSIGN gs_city-places_ref->* TO <ref>.
    SORT <ref> BY place.
    LOOP AT <ref> INTO gs_place.
      WRITE: / gs_city-city_name, gs_place-place.
    ENDLOOP.
  ENDIF.