Ironically, the latter part of what you quoted shows the solution to representing change in an immutable system: create a different stream object instead of mutating the same stream object.

(Streams in this case not being streams in an I/O sense, just an example of a class).

Meh. Once you mutate an object it is not the same object it once was either; you've only maintained a stable memory reference and alias, without the overhead of making a new one.

Yes, that's exactly what I meant. Sorry for not being clearer.