It's probably easiest to find previous discussions here on this topic by searching for 'upvar' (common name for a function that takes advantage of this behavior).
Latest I think was this one [1] but a much earlier discussion is here [2]. [1] https://lists.gnu.org/archive/html//bug-bash/2015-01/msg00018.html [2] https://lists.gnu.org/archive/html/bug-bash/2008-10/msg00107.html
