For the more curious: key-val observing


#1

Page 127 suggests observing keys with:

[self addObserver:self forKeyPath:@"fido" options:NSKeyValueChangeOldKey context:nil];

But that method is declared:

NSKeyValueChangeOldKey is an NSString*, so what’s in your book generates a compile warning. Should this param be one of the NSKeyValueObservingOptions?