Confusion about Depends:, Imports:, Enhances:, import(), inportFrom()

On Thu, Aug 22, 2013 at 10:05 AM, R. Michael Weylandt
<michael.weylandt at gmail.com> <michael.weylandt at gmail.com> wrote:

On Aug 22, 2013, at 9:09, Michael Friendly <friendly at yorku.ca> wrote:

In checking my vcdExtra package, the following NOTE newly appeared (R-Forge, using R version 3.0.1 Patched (2013-08-20 r63635))

Package in Depends field not imported from: ?gnm?
These packages needs to imported from for the case when
this namespace is loaded but not attached.

In the DESCRIPTION file, I have

Depends: R (>= 2.10), vcd, gnm (>= 1.0.3)

In NAMESPACE:

# we are a vcd extension
import(vcd)

I've read 1.1.1 of R-Exts, but it is not clear to me whether I should also import gnm or change
the DESCRIPTION file to use

Imports: vcd, gnm (>= 1.0.3)

R-Exts says: The ?Imports? field lists packages whose namespaces are imported from (as specified in the
NAMESPACE file) but which do not need to be attached, but how can I tell if gnm needs to be attached?

I think the current best practice is to use Imports unless gnm provides functions the end user needs in order to use your package.

Practically, I think this usually comes down to asking whether gnm provides relevant generics -- if you provide methods only, the end user would only be able to call them directly (ick!) unless gnm is both loaded and attached (Depends)

If gnm is tools for your code, but not the user to call directly, Imports is cleaner.

Does that help?

Michael

Also, what is the difference between Imports: in DESCRIPTION and imports() in NAMESPACE?

One enables the other: Imports in DESCRIPTION allows for both imports() and importsFrom(). It could probably be automatic, but the DESC file is much older than the NAMESPACE file.

I pretty sure you can also use import()/importFrom() in NAMESPACE for
packages listed under Depends in DESCRIPTION.

/Henrik

-Michael

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Michael Friendly     Email: friendly AT yorku DOT ca
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