the !!nm := val notation comes from rlang.
!! is quasiquotation, so you can assign to the variable named by nm, not
to nm itself.
:= is an rlang operator that basically works like = but is less fussy,
so you can use !!.
https://rlang.r-lib.org/reference/quasiquotation.html
https://github.com/rstudio/cheatsheets/blob/master/tidyeval.pdf
the !!nm := val notation comes from rlang.
!! is quasiquotation, so you can assign to the variable named by nm, not
to nm itself.
:= is an rlang operator that basically works like = but is less fussy,
so you can use !!.
https://rlang.r-lib.org/reference/quasiquotation.html
https://github.com/rstudio/cheatsheets/blob/master/tidyeval.pdf