[Rd] declaring package dependencies

[Prof Brian Ripley]

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.



>
>>
>> > Attaching it first loads it, then modifies the user's search list so
>> > the user can see it.
>> Which directive does this?
>
> library() and require() both do it.
>
> Duncan Murdoch
>>
>
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-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
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