- (void)loadLocations {
    NSString *url = @"<URL to a text file>";
    NSStringEncoding enc = NSUTF8StringEncoding; 
    NSString *locationString = [[NSString alloc] initWithContentsOfURL:[NSURL URLWithString:url] usedEncoding:&enc error:nil];
    NSArray *lines = [locationString componentsSeparatedByString:@"\n"];

    for (int i=0; i<[lines count]; i++) {
        NSString *line = [lines objectAtIndex:i];
        NSArray *components = [line componentsSeparatedByString:@", "];
        Restaurant *res = [byID objectForKey:[components objectAtIndex:0]];

        if (res) {
            NSString *resAddress = [components objectAtIndex:3];
            NSArray *loc = [NSArray arrayWithObjects:[components objectAtIndex:1], [components objectAtIndex:2]];
            [res.locationCoords setObject:loc forKey:resAddress];   
        }
        else {
            NSLog([[components objectAtIndex:0] stringByAppendingString:@" res id not found."]);
        }
    }
}

There are a few weird things happening here. First, at the two lines where the NSArray lines is used, this message is printed to the console-

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[NSCFDictionary count]: method sent to an uninitialized mutable dictionary object'

which is strange since lines is definitely not an NSMutableDictionary, definitely is initialized, and because the app doesn't crash.

Also, at random points in the loop, all of the variables that the debugger can see will become Invalid. Local variables, property variables, everything. Then after a couple lines they will go back to their original values. setObject:forKey never has an effect on res.locationCoords, which is an NSMutableDictionary. I'm sure that res, res.locationCoords, and byId are initialized.

I also tried adding a retain or copy to lines, same thing. I'm sure there's a basic memory management principle I'm missing here but I'm at a loss.