"An example of a copy that's disguised rather than hidden is a hash function, which has all the memory-access cost of a copy and also involves more computation.

"An example of a copy that's disguised rather than hidden is a hash function, which has all the memory-access cost of a copy and also involves more computation." A hash function requires reading all the input, but it only writes to a constant-sized region of memory, unlike a memory copy. I'd say this difference makes the comparison pretty inaccurate.