[Swarm-Support] did gcc change the way "message to nil" is handled?

[Paul Johnson]

I am trying to find a bug in a big program. A nil gets inserted at the 
very end of the collection, and somehow that magically makes the loop go 
over and over. Its a loop like this:

for( aThing=[index next];[index getLoc]==Member;[aThing=[index next]])

Very confounding, I can't figure how the nil gets in there.

Anyway, while bug shooting I started to suspect some monkey business 
with Swarm collections and the old [index remove] as applied to the last 
element.  So I made a test app to see if removing the last item with 
that method caused the nil to appear at the end.

It did not unearth the cause of my trouble, but it did reveal another 
problem with gcc-3.3.2 and Swarm-2.1.150.  Now, you can send messages to 
nil and no error is returned.  It just returns a 0.  This is the way it 
had worked a long time ago, but about 3 years ago, we started getting 
errors about sending messages to nils.

If you run the attached, you see it doesn't give any errors when nils 
are told to do things.

I'm thinking this is bad, how about you?  I used to think it was good, 
but that was when I was a lazier programmer.

If you've ever had the problem of a nil magically appearing at the end 
of a collection and causing an index to malfunction and repeat over and 
over, I'd be glad to know.

--
Paul E. Johnson                       email: address@hidden
Dept. of Political Science            http://lark.cc.ku.edu/~pauljohn
1541 Lilac Lane, Rm 504
University of Kansas                  Office: (785) 864-9086
Lawrence, Kansas 66044-3177           FAX: (785) 864-5700

#import <simtools.h>
#import <defobj/Create.h>
#import <objectbase.h>
#import <objectbase/SwarmObject.h>
#import <random.h>
#import <collections.h>

@interface Bug: SwarmObject
{
  int RI;
}

- setRI: (int) x;
- (int)getRI;

@end

@implementation Bug

-setRI: (int)x
{
  RI= x;
  printf("RI is %d \n",x);
  return self;
}

- (int)getRI
{
  return RI;
}

@end


int
main (int argc, const char **argv)
{
  id aCollection, index;
  id aThing;
  int i;
  initSwarm (argc, argv);
  aCollection = [List create: globalZone];

  for (i =0; i< 100; i++)
    {
      [aCollection addFirst: [[Bug create: globalZone] setRI: i]];
      fprintf(stderr,"collection getcount %d \n",[aCollection getCount]);
    }

  index = [aCollection begin: globalZone];
  for ( aThing = [index next]; [index getLoc]==Member; aThing=[index next])
    {
      fprintf(stderr,"first RI=%d\n", [aThing getRI]);
    }

  [index drop];


 [aCollection atOffset: 99 put: nil];
  index = [aCollection begin: globalZone];
  for ( aThing = [index next]; [index getLoc]==Member; aThing=[index next])
    {
      fprintf(stderr,"second RI=%d\n", [aThing getRI]);
      if ([aThing getRI] == 0)
        [index remove];
    }

  [index drop];


  fprintf(stderr,"aCollection has %d elements\n",[aCollection getCount]);
  fprintf(stderr,"here's an object %d \n",[[aCollection atOffset: 97] getRI]);
  [aCollection atOffset: 97 put: nil];
  fprintf(stderr,"I just put a nil in the last spot in the list\n");
  index = [aCollection begin: globalZone];
  for ( aThing = [index next]; [index getLoc]==Member; aThing=[index next])
    {
      fprintf(stderr,"third RI=%d\n", [aThing getRI]);
      if (!aThing)fprintf(stderr,"yes, that last one was a nil!\n");
    }

  [index drop];
  return 0;
}

/* 
Local Variables: 
compile-command: "$SWARMHOME/bin/libtool-swarm --mode=link gcc -D_GNU_SOURCE 
-Wall -o listWithNil  -g -Wno-import \
-I$SWARMHOME/include -I$SWARMHOME/include/swarm -L$SWARMHOME/lib \
-L$SWARMHOME/lib/swarm listWithNil.m -lswarm -lobjc " 
End: 
*/