[Rd] Question about selective importing of package functions...

[Gabor Grothendieck]

On Sun, Oct 20, 2013 at 4:49 PM, Duncan Murdoch
<murdoch.duncan at gmail.com> wrote:
> On 13-10-20 4:43 PM, Jonathan Greenberg wrote:
>>
>> I'm working on an update for my CRAN package "spatial.tools" and I noticed
>> a new warning when running R CMD CHECK --as-cran:
>>
>> * checking CRAN incoming feasibility ... NOTE
>> Maintainer: 'Jonathan Asher Greenberg <spatial-tools at estarcion.net>'
>> Depends: includes the non-default packages:
>>    'sp' 'raster' 'rgdal' 'mmap' 'abind' 'parallel' 'foreach'
>>    'doParallel' 'rgeos'
>> Adding so many packages to the search path is excessive
>> and importing selectively is preferable.
>>
>> Is this a warning that would need to be fixed pre-CRAN (not really sure
>> how, since I need functions from all of those packages)?  Is there a way
>> to
>> import only a single function from a package, if that function is a
>> dependency?
>
>
> You really want to use imports.  Those are defined in the NAMESPACE file;
> you can import everything from a package if you want, but the best style is
> in fact to just import exactly what you need.  This is more robust than
> using Depends, and it doesn't add so much to the user's search path, so it's
> less likely to break something else (e.g. by putting a package on the path
> that masks some function the user already had there.)

That may answer the specific case of the poster but how does one
handle the case
where one wants the user to be able to access the functions in the
dependent package.

For example, sqldf depends on gsubfn which provides fn which is used
with sqldf to
perform substitutions in the SQL string.

library(sqldf)
tt <- 3
fn$sqldf("select * from BOD where Time > $tt")

I don't want to ask the user to tediously issue a library(gsubfn) too since
fn is frequently needed and for literally years this has not been necessary.
Also I don't want to duplicate fn's code in sqldf since that makes the whole
thing less modular -- it would imply having to change fn in two places
if anything
in fn changed.

-- 
Statistics & Software Consulting
GKX Group, GKX Associates Inc.
tel: 1-877-GKX-GROUP
email: ggrothendieck at gmail.com