Re: probes

[Ken Cline]

Doug,

Did you solve this problem?  I didn't see a response on the
mailing list... maybe I missed it?

On Tue, 14 Jul 1998, Chimera wrote:

> All right, a swarm programming question.
> 
> I have a subclass of my basic Cell class.  The probe map for it (when I
> right click on the 2-D grid display) only comes up with the variables in
> the subclass.  I tried to make a custom probe map of the subclass, also
> including the variables that I wanted from the superclass.  As I
> suspected, it does not like including variables from its parent.
> Perhaps it is in the midst of puberty?  Anyway, the quick fix is just to
> redefine the variables in the subclass.  However, following the present
> working environment of not sidestepping issues, I decided to ask if
> there is a "correct" way of doing this.  Any suggestions?
> 

I haven't done any Swarm/ObjC programming in ages, but in
the old days ;)...

   [ probeMap addProbe:
       [ probeLibrary getProbeForVariable: "foo"
                                  inClass: [self superClass] ] ];

where "foo" is the variable defined in the super class.
Does this no longer work?

With custom probe maps you have to specify exactly which
class in the hierarchy that defines the variable (correct me
if I'm wrong, folks).  This adds a lot of flexibility but it
can also cause some headaches: move a variable between your
superclasses and you're forced to start picking though all
the subclasses.  This also means that apps can become much
more entangled with the libs they use.

To make your subclass's code more robust, you might try
"initializing" the probeLibrary with a CompleteProbeMap (see
example code below). The CompleteProbeMap (still?) has code
that climbs the super class tree probing all the variables
and methods.  Alternatively, use a CompleteProbeMap as a
(local) resource instead of probeLibrary.  I think either
way would be valid, though I never tried it myself, of
course. :)

I hope that helps.

Ken.

PS: You shouldn't need to create the CompleteProbeMap
    more than once, ie when the first instance of your
    subclass is created.  For that reason you might
    consider using a class method or class variable, as
    appropriate.  Actually, it isn't necessary to create a
    probe map for any class more that once since the probe
    library stores the map by class.  However, if you
    start to use some conditional method like probeLibrary's
    "isProbeMapDefinedFor:", then you'll need to be careful
    that some superclass method which gets executed first
    (eg createBegin) doesn't end up taking credit for
    defining the subclass's probe map.  (Hmmm.... maybe I'm
    getting confused... like I said, its been awhile.  =;-)

---------------------------------------------------------
Example code... 
(This was taken out of context => might not work as is...)

/**
 * Sets the class's probeMap with the char *'s provided in
 * the variable argument list.  A ":" char * is used to
 * divide the ivar names from the imethod names in the
 * va_list.  That is, the usage is something like:
 *
 *   "var1", "var2", ..., ":", "method1", "method2",..., NULL
 *
 * This is the same syntax that CustomProbeMap uses.
 *
 */
-setProbes: (char *) args, ...
{
   va_list  argptr  = NULL;
   Class    class   = NULL;
   id <ProbeMap> probeMap     = NULL;
   char *        probeName    = NULL;
   id <Probe>    probe        = NULL;
   SEL           getProbeSEL  = NULL;
 
   va_start( argptr, args );
   class = [ self class ];
 
   [ probeLibrary setProbeMap: [self getCompleteProbeMap] For: class ];
   probeMap  = [ [ [ CustomProbeMap createBegin: [self getZone] ]
                                 setProbedClass: class ] createEnd ];
   probeName    = args;
   getProbeSEL  = M(getProbeForVariable:inClass:);
 
   while ( probeName && strlen( probeName ) ) {
      if ( probeName[0] == ':' ) {
         getProbeSEL  = M(getProbeForMessage:inClass:);
         probeName    = va_arg( argptr, char * );
         continue;
      }
      probe = [ probeLibrary perform: getProbeSEL with: (id)probeName
                                                  with: (id)class     ];
      // Should I copy the probe instead of passing it in directly?
      if ( probe )
         [ probeMap addProbe: probe ];
      else
         raiseEvent( WarningMessage, "\t> Probe does *NOT* exist in 
`probeLibrary'.\n"  \
                                     "\t> Unable to get probe `%s' for class 
`%s'.\n",  \
                                          probeName, [ class name ]             
        );
      probeName = va_arg( argptr, char * );
   }
 
   [ probeLibrary setProbeMap: probeMap For: class ];
   va_end( argptr );
 
   return self;
}
 



_________________________________________________________
Ken Cline                             address@hidden
SAIC                                 VOICE (410) 571-0413
Annapolis, MD                          FAX (301) 261-8427




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