Upcoming NAMESPACE, Depends, Imports changes for 2.14.0 (some definitions/use please)

Question

If you are a package author, you are hopefully well aware of upcoming changes in package structure when we move to 2.14 in about a week. One of the changes is that all pack

Answer 1

I'm going to answer my own question with a few details I've learned after switching several packages over to R 2.14.

The description above from the manual sort of gives the impression that whatever you had in Depends: for R 2.13 should be moved over to Imports: in R 2.14. You should do that, but they are not 1-for-1 functionally the same, as I hope will be clear from the notes below.

Here we go:

Depends: should probably be used only for restrictions on versions, like 'R >= 2.10' or 'MASS > 0.1' and nothing else under R 2.14.

Having a namespace is partly a mechanism of notifying users that there may be name conflicts and "replacements" -- in other words overwriting of names in use. The NAMESPACE file must match in items and in order the Imports: field in DESCRIPTION. Function names etc imported will be listed under "loaded via namespace (and not attached)" in sessionInfo(). Those packages are installed but not loaded (i.e. no library(some imported package)).

The other role of a namespace is to make functions available to your package "internally". By that, I mean that if your package uses a function in an imported package, it will be found.

However, when you have an example in an .Rd file to be run during checking, packages that you used to have under Depends: in R 2.13 but are now in Imports: under R 2.14 are not available. This is because the checking environment is pretty much like sourcing a script in a clean environment (assuming you are using R --vanilla so .Rprofiles etc have not been run). Unless you put a library(needed package) statement in your example, it won't work under R 2.14 even if it did under R 2.13. So the old examples do not necessarily run even though your package Imports: the needed packages, because again Imports: is not quite the same as Depends: (strictly, they are attached but not loaded).

Please do correct me if any of this is wrong. Many thanks to Hadley Wickham and others who helped me along!