[Freeciv-Dev] Re: [RFC] Caching AI values

[Raimar Falke <hawk@xxxxxxxxxxxxxxxxxxxxxxx>]

On Wed, Mar 20, 2002 at 07:16:37PM +0000, Gregory Berkolaiko wrote:
> On Tue, 19 Mar 2002, Raimar Falke wrote:
> 
> > On Tue, Mar 19, 2002 at 08:36:02PM +0000, Gregory Berkolaiko wrote:
> > > 
> > > That might be right, but let's have a look at the overall picture:
> > > 1. Unit A thinks about moving to city C to kill things around.  The 
> > > number 
> > > of things to kill around C is calculated and recorded in struct city C.
> > > ----
> > 
> > > 2. we are doing other stuff, but whenever we kill a unit, we have to 
> > > figure out if it was counted in the targets_around_C and if it was, 
> > > subtract its value
> 
> I thought this problem over and I got this great idea which, it seems, is 
> the same as you propose below (although I do not fully understand your 
> wording):
> 
> If a unit is killed, we call a function which does not recalculate 
> anything by itself, but instead increments some "time" variable to show 
> that the cached values have expired.  Then, the next time we try to access 
> cached values, we will have to recalculate them.  This way we do not 
> recalculate anything that isn't going to be used and avoid all these 
> complex decisions "what to update" as well.
> 
> Of course each type of cached values will have it's own "time" variable 
> associated with it.

This is known as lazy evaluation. You don't need a time field. A
simple bit "valid" is sufficient.

        Raimar

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