[freeciv-ai] Re: Goto coordinates and ai roles

[Raimar Falke <rf13@xxxxxxxxxxxxxxxxx>]

On Mon, Jan 20, 2003 at 10:45:36PM -0500, Jason Dorje Short wrote:
> Mike Kaufman wrote:
> >On Sat, Jan 18, 2003 at 12:05:39PM -0500, Ross W. Wetmore wrote:
> >
> >>If you cannot rely on an arbitrary map_position to represent an invalid
> >>position (i.e. all map positions are potentially valid), then you need an
> >>extra bit of information somewhere. There are two common ways to do this.
> >>
> >>Set a goto_active guard bit and do things like 
> >> if (punit->goto_active) {
> >>   /* punit->goto_dest_x, punit->goto_dest_y accesses */
> >> }
> >>
> >>Make the goto_dest a map_position pointer and use null as the guard test.
> >> if (punit->goto_dest) {
> >>   /* punit->goto_dest->x, punit->goto_dest->y accesses */
> >> }
> >>
> >>Note, the pointer can point back into the punit structure, so you don't
> >>need to track extra memory allocations, and can in fact directly access 
> >>the punit goto(x,y) values if necessary, bypassing the guard check. The
> >>pointer acts very much as a guard test that allows you to turn the goto
> >>map_position on and off.
> >>
> >>Both of these mean breaking backwards compatibility for the (-1,-1)
> >>error assumptions including over network communications. But the tests
> >>are much simpler than a same_pos() or some unnormalized version to
> >>detect the special case. 
> >
> >
> >yes, either of these is far better than (-1,-1) which I've never ever had a
> >good feeling about. Take your pick really, but I prefer the the 
> >map_position
> >pointer because it's cleaner...
> 
> I agree.  I remember Raimar vetoing this idea a *long* time ago, but 
> that was for (IIRC) using pointers to positions for events (e.g., the 
> vnotify_conn_ex argument), as opposed to goto destinations.  I believe 
> his reasons were (1) (-1,-1) should be used over the network anyway to 
> preserve backward-compatability, and (2) using a pointer is slower.

(3) memory leaks you may get with this. So I'm for exactly two places
where this struct of the position is allocated and freed.

        Raimar

-- 
 email: rf13@xxxxxxxxxxxxxxxxx
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