expose()
returns a sentinel object, similar in spirit to NULL
, that tells
the calling function to return its internal data structure. googledrive
stores alot 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.