Using `ensurer` to QA elements of a `data.frame`

ensurer-example-data_frame.R

library(ensurer)

ensure_none_missing <- ensures_that(!any(is.na(.)) ~ "There are missing values")
ensure_all_positive <- ensures_that(all(int(.)) > 0 ~ "Not all values are positive", +ensure_none_missing)

# Everything works as expected with a simple vector
x <- 1:4
x %>% ensure_all_positive

# Now let's try testing element(s) of a data.frame
test_data <- data.frame(foo = x, bar = rep(-Inf, length(x))) 
test_data %>% 
  ensure(all(.$foo > 0)) %>%  # passes silently, as expected
  ensure_all_positive(.$foo)  # FAILS with "unused argument (.$foo)" ... why?