Dictionaries are a concept of types modelled after R environments. Dictionaries are containers of R objects that:
Contain uniquely named objects.
Can only be indexed by name. They must implement the extracting
operators $ and [[. The latter returns an error when indexed
by position because dictionaries are not vectors (they are
unordered).
Report a clear error message when asked to extract a name that
does not exist. This error message can be customised with the
lookup_msg constructor argument.
as_dictionary(x, lookup_msg = NULL, read_only = FALSE)is_dictionary(x)
An object for which you want to find associated data.
An error message when your data source is accessed inappropriately (by position rather than name).
Whether users can replace elements of the dictionary.
Dictionaries are used within the tidy evaluation framework for
creating pronouns that can be explicitly referred to from captured
code. See eval_tidy().