> 2. Copying memory ... the entire point of some of the immutable structures is hidden in their implementations, such that they are fast exactly because they d

> 2. Copying memory ... the entire point of some of the immutable structures is hidden in their implementations, such that they are fast exactly because they do NOT copy unnecessarily. the side effect gets called "functional", so there's a strange reversal of importance of (kinda misleading) buzzwords at play here. The link(s) the others shared is a great article.