vars() is superseded because it is only needed for the scoped verbs (i.e.
summarise_at(), and friends), which have been been
superseded in favour of
vignette("colwise") for details.
This helper is intended to provide tidy-select semantics for scoped verbs
summarise_at(). Note that anywhere you can supply
vars() specification, you can also supply a numeric vector of column
positions or a character vector of column names.
tidy-select> Variables to operate on.