expose()
returns a sentinel object, similar in spirit to NULL
, that tells
the calling function to return its internal data structure. googledrive
stores a lot of information about the Drive API, MIME types, etc., internally
and then exploits it in helper functions, like drive_mime_type()
,
drive_fields()
, drive_endpoints()
, etc. We use these objects to
provide nice defaults, check input validity, or lookup something cryptic,
like MIME type, based on something friendlier, like a file extension. Pass
expose()
to such a function if you want to inspect its internal object, in
its full glory. This is inspired by the waiver()
object in ggplot2.