I have the book too. It's interesting as a history lesson and initial motivations for Objective-C.
In particular, in the beginning Objective-C was a lot looser typed at compile time than it is now: no NSString* or NSWindow*, it was all just id. It was an attempt to make C look like Smalltalk.
The language eventually evolved more toward the static-typed end of the spectrum, culminating in support for lightweight generics and ostensibly birthing Swift along the way.
In particular, in the beginning Objective-C was a lot looser typed at compile time than it is now: no NSString* or NSWindow*, it was all just id. It was an attempt to make C look like Smalltalk.
The language eventually evolved more toward the static-typed end of the spectrum, culminating in support for lightweight generics and ostensibly birthing Swift along the way.