[Freeciv-Dev] Re: (PR#6941) Mission Orders

["Arnstein Lindgard" <a-l@xxxxxxx>]

<URL: http://rt.freeciv.org/Ticket/Display.html?id=6941 >

On Wed, 28 Jan 2004 10:42:25 -0800 Jason Short wrote:

> struct unit_order {
>    enum orders_type type;
>    union {
>      enum unit_orders order;
>      enum unit_activity activity;
>      enum unit_actions action;
>      enum diplomat_actions diplomat;
>    } order;
>    enum direction8 dir;
> }
> 
> Is this also illegal?  It does have a name now.

It seems legal, but I need to reference the order (union) in places
where the "struct unit_order" isn't relevant, so why not declare the
union outside, when you have a name for it already.

> How do you know whether a 0 is the first 
> order or the first activity?

I did this:

enum unit_activity {
  ACTIVITY_IDLE,
  ...
  ACTIVITY_LAST   /* leave this one last */
};
enum unit_actions {
  ACTION_AUTO_ATTACK = (ACTIVITY_LAST + 1),
  ...
  ACTION_LAST   /* leave this one last */
};
enum diplomat_actions {
  DIPLOMAT_BRIBE = (ACTION_LAST + 1),
  ...
  DIPLOMAT_ANY_ACTION   /* leave this one last */
};
enum unit_orders {
  ORDER_MOVE = (DIPLOMAT_ANY_ACTION + 1),
  ...
};

> If the type doesn't need to be associated with the union, how do you 
> tell which type the union is?

I simply use order.action when I know I'm dealing with an action,
and order.activity when I know I have an activity. That's only for
cosmetic reasons, as is the entire union in the first place.

I think the most straightforward implementation would be:

  struct unit_order {
     int order;
     enum direction8 dir;
  };

and reference "order" by any name, whether ACTIVITY_*, ACTION_* or ORDER_*,
because enums ARE integers in C, as far as I can see. I sort of thought it
was fancy to see if I could find a use for that strange union thing.. or
maybe I thought someone would protest against putting enums in integers
without cast because that's not allowed in C++ and thus avoid another
pointless monster debate.

In the patch I do:

union composite_orders {
  enum unit_orders    order;
  enum unit_activity  activity;
  enum unit_actions   action;
};

struct unit_order {
  union composite_orders composite;
  enum direction8 dir;
};

  switch (order.composite.order) {
    case ORDER.MOVE:
    ...
    case ACTIVITY_SENTRY:
    ...
    case ACTION_UNLOAD:
    ...
  }

But of course, to make it pedantic we could have:

  switch (order.composite.order) {
    case ORDER.MOVE:
    ...
    default:
      switch (order.composite.activity) {
        case ACTIVITY_SENTRY:
        ...
        default:
          switch (order.composite.action) {
            case ACTION_UNLOAD:
            ...
          }
      }
  }

..and then the assembler could laugh at us for handling a simple
integer in the most complex fashion possible :-)

Anyway, I like having separate enums for ACTIVITY_* and ORDER_* etc.


Arnstein