> I believe that your interpretation of what’s actually happening is what’s baloney.

I'm actually quoting Prof Andrew Appel of Princeton: https://www.cs.princeton.edu/~appel/papers/ssafun.pdf

You seem to think that functional programming and in-place updates are mutually exclusive. This is not the case, e.g. Haskell supports mutation as a tracked and controlled side-effect. It can even give static guarantees that a function is pure even it uses mutation internally. Recent research even suggests that compilers can add the in-place updates for us: https://www.microsoft.com/en-us/research/publication/fp2-ful...