Using the dot (`.`) in `fail_with`

ensurer-fail_with-experiments.R

#
# Context:
#
#  https://cran.r-project.org/web/packages/ensurer/vignettes/ensurer.html says:
#  "It is also possible to use the dot, ., directly in anonymous error handlers defined directly in the call to e.g. ensure_that."
#
# I must be misunderstanding the statement above!
#

library(ensurer)

ensure_only_one <- ensures_that(
  length(.) == 1,
  fail_with = function (err) paste0("Expecting 1 value but got ", length(.)))

ensure_only_one(LETTERS) # I expect this to yield "got 26" but it yields "got 2" (???)