o(ther)l/log

Some time ago, I discovered this neat little tool, LJV (for "Lightweight Java Visualizer"). Basically, a small Java program that takes a data structure as input, and generate a GraphViz file as output.

So of course, I had this irrepressible urge to hack something similar for Objective-C.

Let's take the following Obj-C code:

@interface Bi : NSObject {
        NSString* xxa;
}
@end

@interface Bo : Bi {
        NSString* d;
        id e;
}
@end

@implementation Bo 
-(id)init
{
        [super init];
        e = [[NSScanner scannerWithString:@"asdfasdf asdf"] retain];
        return self;
}
@end

@interface Ga : NSObject {
        NSString* grunt;
        NSMutableArray* a;
        Bo* x;
}
@end

@implementation Ga 
-(id)init
{
        [super init];
        grunt = @"pok";
        a = [[NSArray alloc] initWithObjects:@"ag",
                                   [NSString stringWithString:@"b"],
                                   nil];
        x = [[Bo alloc] init];
        return self;
}
@end

(yes, I know, I did not code release methods, I'm leaking). Just use some magical NSObject category:

And shazam !

Some additional notes:

• Objective-C is not Java, and introspection API is simpler, but /usr/include/objc/objc-class.h and friends are enough for this.
• This works reasonably well, even for some large programs, with one caveat: if you have garbage in one of your ivar, you're dead. It's not a problem most of the time but when I tried this on some AppKit code, it crashed. This could be fixed by maintaining a list of classes that should not be introspected.
• I need to cleanup the source code and put this on the web somewhere.

update: I wrote a new post with additional explanations and the source code on