Re: Variant records..

["Robert I. Eachus" <rieachus@comcast.net>]

Ganesh Ramasivan wrote:

> Anyways, in the case above, how can I pass a second discriminant. This
> is because I need to be able to select a particular command for a
> particular radar.

One way is:

  type RADAR_TYPE_CHOICE is (RADAR_A, RADAR_B);

  type RADAR_COMMAND_CHOICE is (RADAR_STATE,
                                RADAR_MODE,
                                RADAR_DISPLAY_RANGE_SELECT);

  type RADAR_COMMAND_TYPE
       (RADAR_TYPE_CHOICE := RADAR_A;
        RADAR_COMMAND_CHOICE := RADAR_STATE)is
     record
       case RADAR_COMMAND_CHOICE is
       when RADAR_DISPLAY_RANGE_SELECT =>
         < a whole bunch of parameters...>
         case RADAR_TYPE_CHOICE is
         when RADAR_A =>
           <Radar A specific parameters>
         when RADAR_B =>
           <Radar B specific parameters>
         end case;
       when others =>
         null;
       end case;
     end record;

But with this approach, you can't have indentically named elements that 
are of different types or subtypes for Radars A and B.  You can of 
course give those parameters different names.

Or you can have:

     type Radar_A_Display_Range_Select is...
     type Radar_B_Display_Range_Select is...

type RADAR_COMMAND_TYPE
       (RADAR_TYPE_CHOICE := RADAR_A;
        RADAR_COMMAND_CHOICE := RADAR_STATE)is
     record
       case RADAR_COMMAND_CHOICE is
       when RADAR_DISPLAY_RANGE_SELECT =>
         case RADAR_TYPE_CHOICE is
         when RADAR_A =>
              RADAR_A_DISPLAY_RANGE: RADAR_A_DISPLAY_RANGE_SELECT;
         when RADAR_B =>
              RADAR_B_DISPLAY_RANGE: RADAR_B_DISPLAY_RANGE_SELECT;
         end case;
       when others =>
         null;
       end case;
     end record;

The potential probleme with this approach is the potentially long names 
for the individual elements.  However, if you set the command via an 
aggregate, that problem goes away.  (Unless your software development 
plan requires named notation for aggregates. ;-)

Either style works.  Does this answer your question?

-- 
                                           Robert I. Eachus

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