[Rd] declaring package dependencies

[Duncan Murdoch]

On 13/09/2013 10:37 AM, Prof Brian Ripley wrote:
> On 13/09/2013 14:51, Duncan Murdoch wrote:
> > On 13/09/2013 8:31 AM, Michael Friendly wrote:
> >> On 9/12/2013 1:37 PM, Duncan Murdoch wrote:
> >> >
> >> > I think this one would be fine if you had library(MASS) or
> >> > require(MASS) or (probably best) used MASS::loglm explicitly.  It may
> >> > be that in the past some other package put MASS on the search list,
> >> > and that's why it worked before.
> >> >
> >> > The distinction is between "loading" and "attaching" a package.
> >> > Loading it (which would be done if you had MASS::loglm, or imported
> >> > it) guarantees that the package is initialized and in memory, but
> >> > doesn't make it visible to the user without the explicit MASS::
> >> > prefix.  Attaching it first loads it, then modifies the user's search
> >> > list so the user can see it.
> >> >
> >> > Loading is less intrusive, so it's preferred over attaching.  Both
> >> > library() and require() would attach it.
> >> >
> >> Thanks for this explanation, but I'm still confused about how to avoid
> >> the wrath of the CRAN-devel
> >> daemon, whose appetite for new morsels of developer flesh seems ever
> >> increasing and makes
> >> keeping even a stable package up-to-date a moving target.  Perhaps such
> >> changes in R devel
> >> should be announced on this list for public comment before they are
> >> enforced in R CMD check.
> > Changes are generally announced in the NEWS.Rd file long before release,
> > but R-devel is an unreleased version, so you won't see the news until it
> > is there.  Announcing things that nobody can try leads to fewer useful
> > comments than putting them into R-devel where at least people can see
> > what is really happening.
> >>
> >> In vcdExtra, I use MASS::loglm in ~ 6 .Rd examples, a vignette, and also
> >> provide R code that
> >> extends *.loglm methods.  All of this previously worked by including
> >> Suggests: MASS, ...
> >> Changing this to Imports: MASS seems rather heavy-handed; I don't really
> >> want/need all of MASS
> >> in my namespace, and using MASS::loglm in examples seems ugly.  For now,
> >> I'll use
> >> require(MASS) in each example.
> >
> > If you need a small number of things from MASS in your package code,
> > then importing them explicitly is definitely the way to go, e.g.
> > importFrom(MASS, loglm).  If you only use them in examples, I wouldn't
> > do that, I'd recommend Suggests and use the MASS:: prefix. Whether that
> > is ugly is a matter of taste:  it makes it clear to a user where that
> > function came from, and doesn't potentially hide objects from other
> > packages later in the search path.
> >
> > On the other hand, require(pkg) is really simple; we have no equivalent
> > function that only does the loading, without attaching.
> > So it's hard to write
> >
> > if (requireLoadable(MASS)) {
> >    MASS::loglm( ... )
> > }
>
> ?requireNamespace.

Thanks.  I'll switch my packages to use that.

Duncan Murdoch