Why Hide Command?

Question

Hi Experts,
Why do we use HIDE command, it consums memory when we hide data.
In place of Hide we can use
1. sy-lisel
2. Get cursor
3. Read line
etc. which don't consum memory.
Please give me reason, where it is necessary.
Regards
Rajiv singh.

Answer 1

HI.
HIDE
The HIDE statement is one of the fundamental statements for interactive reporting. You use the HIDE technique when creating a basic list. It defines the information that can be passed to subsequent detail lists.
You use the HIDE technique while creating a list level to store line-specific information for later use. To do so, use the HIDE statement as follows:
HIDE <f>.
This statement places the contents of the variable <f> for the current output line (system field SY-LINNO) into the HIDE area. The variable <f> must not necessarily appear on the current line.
To make your program more readable, always place the HIDE statement directly after the output statement for the variable <f> or after the last output statement for the current line.
As soon as the user selects a line for which you stored HIDE fields, the system fills the variables in the program with the values stored. A line can be selected
by an interactive event.
For each interactive event, the HIDE fields of the line on which the cursor is positioned during the event are filled with the stored values.
by the READ LINE statement.
You can think of the HIDE area as a table, in which the system stores the names and values of all HIDE fields for each list and line number. As soon as they are needed, the system reads the values from the table.
The example below presents some of the essential features of interactive reporting. The basic list contains summarized information. By means of the HIDE technique, each detail list contains more details.
GET CURSOR
Use the statements GET CURSOR FIELD and GET CURSOR LINE to pass the output field or output line on which the cursor was positioned during the interactive event to the ABAP program.
READ LINE
Use the statements READ LINE and READ CURRENT LINE to read data from the lines of existing list levels. These statements are closely connected to the HIDE technique.
The following program is connected to the logical database F1S.
REPORT demo_list_hide NO STANDARD PAGE HEADING.
TABLES: spfli, sbook.
DATA: num TYPE i,
      dat TYPE d.
START-OF-SELECTION.
  num = 0.
  SET PF-STATUS 'FLIGHT'.
GET spfli.
  num = num + 1.
  WRITE: / spfli-carrid, spfli-connid,
           spfli-cityfrom, spfli-cityto.
  HIDE:    spfli-carrid, spfli-connid, num.
END-OF-SELECTION.
  CLEAR num.
TOP-OF-PAGE.
  WRITE 'List of Flights'.
  ULINE.
  WRITE 'CA  CONN FROM                 TO'.
  ULINE.
TOP-OF-PAGE DURING LINE-SELECTION.
  CASE sy-pfkey.
    WHEN 'BOOKING'.
      WRITE sy-lisel.
      ULINE.
    WHEN 'WIND'.
      WRITE:  'Booking', sbook-bookid,
           /  'Date   ', sbook-fldate.
      ULINE.
  ENDCASE.
AT USER-COMMAND.
  CASE sy-ucomm.
    WHEN 'SELE'.
      IF num NE 0.
        SET PF-STATUS 'BOOKING'.
        CLEAR dat.
        SELECT * FROM sbook WHERE carrid = spfli-carrid
                            AND   connid = spfli-connid.
          IF sbook-fldate NE dat.
            dat = sbook-fldate.
            SKIP.
            WRITE / sbook-fldate.
            POSITION 16.
          ELSE.
            NEW-LINE.
            POSITION 16.
          ENDIF.
          WRITE sbook-bookid.
          HIDE: sbook-bookid, sbook-fldate, sbook-custtype,
                sbook-smoker, sbook-luggweight, sbook-class.
        ENDSELECT.
        IF sy-subrc NE 0.
          WRITE / 'No bookings for this flight'.
        ENDIF.
        num = 0.
        CLEAR sbook-bookid.
      ENDIF.
    WHEN 'INFO'.
      IF NOT sbook-bookid IS INITIAL.
        SET PF-STATUS 'WIND'.
        SET TITLEBAR 'BKI'.
        WINDOW STARTING AT 30 5 ENDING AT  60 10.
        WRITE: 'Customer type   :', sbook-custtype,
             / 'Smoker          :', sbook-smoker,
             / 'Luggage weight :', sbook-luggweight UNIT 'KG',
             / 'Class           :', sbook-class.
      ENDIF.
  ENDCASE.
Reward all helpfull answers.
Regards.
Jay