peek_vars() returns the vector of names of the variables
currently available for selection.
peek_data() returns the whole input vector (only available with
eval_select()).
Read the Get started for
examples of how to create selection helpers with peek_vars().
The variable names in a selection context are registered
automatically by eval_select() and eval_rename() for the
duration of the evaluation. peek_vars() is the glue that connects
selection helpers to the current selection
context.
peek_vars(..., fn = NULL)peek_data(..., fn = NULL)
These dots are for future extensions and must be empty.
The name of the function to use in error messages when the helper is used in the wrong context. If not supplied, a generic error message is used instead.