[Rd] Imports problem

Therneau, Terry M., Ph.D. therneau at mayo.edu
Mon Feb 16 15:04:47 CET 2015

On 02/16/2015 07:35 AM, Duncan Murdoch wrote:
> If you are depending on nlme, you don't also need to import it. But it
> is generally a good practice to avoid either modifying or relying on the
> search list:  as people get more packages there, there are more chances
> for clashes.
I would suggest adding the second sentence above to the "Writing R extensions" manual.  At 
least for me, it made the :: argument much clearer in the following paragraph (found 
there).  Before the "why" was a bit mysterious, now I have a motivation to make some of 
these changes in my own code.

"R code in the package should call library or require only exceptionally. Such calls are 
never needed for packages listed in ‘Depends’ as they will already be on the search path. 
It used to be common practice to use require calls for packages listed in ‘Suggests’ in 
functions which used their functionality, but nowadays it is better to access such 
functionality via :: calls."

I disagree with the above sentence in one case, however.  That is in a vignette where one 
is showing the user a direction that they might go themselves.  For example I'm currently 
working on a competing risks vignette for the survival package which shows how to do a 
particular analysis and then has a section on "if you choose to fit a Fine-Gray model 
instead, this is how it compares".  Since any user who wanted to fit that model would 
themselves start with "library(cmprsk)", the vignette does so too.  My argument is 
pedagogical rather than technical.

Last note: your first sentence clashes with one in the Writing R extensions manual. 
"Almost always packages mentioned in ‘Depends’ should also be imported from in the 
NAMESPACE file: this ensures that any needed parts of those packages are available when 
some other package imports the current package."

More information about the R-devel mailing list