gistfile1.m

// In the interface:
@interface TransferFunction : NSObject {
     id <TransferFunctionDrawingDelegate> _delegate;
}
@property (nonatomic, weak) id <TransferFunctionDrawingDelegate> delegate;

// In the implementation:
@synthesize delegate=setDelegate;

- (void)setDelegate:(id <TransferFunctionDrawingDelegate>)delegate {
    _delegate = delegate;
    [delegate recreatePath:self.points];
    assert(delegate != nil);
}

// The _delegate iVar works, but the property doesn't:
(gdb) p [_tf delegate]
$1 = (struct objc_object *) 0x0
(gdb) p _tf._delegate
$2 = (struct objc_object *) 0xb24e420