Derive a pkg data field, giving a function by which a piece of package
data is calculated. This function is not called directly, it used by the
indexing functions implemented for pkg to populate new data fields.
Default implementations accept field as a character, automatically
dispatching on the field as a class object, and accept a missing
resource, instead iterating through pkg resources by priority.
Arguments
- pkg
A
pkg()- resource
A
resource(), or if not provided, theresourceextracted frompkg@resource.- field
Used for dispatching on which field to derive. Methods are provided such that a simple
characterfield name can be passed and used to build a class for dispatching to the right derivation function.- ...
Used by specific methods.
Details
This function is used internally when accessing a pkg object using $,
[[ and [.
See also
Other generics:
pkg_data_info()