[R] packagename:::functionname vs. importFrom

[Martin Morgan]

On 01/03/2011 09:06 PM, Hadley Wickham wrote:
>> Correct.  I'm doing this because of non-exported functions in other packages,
>> so I need :::
> 
> But you really really shouldn't be doing that.  Is there a reason that
> the package authors won't export the functions?
> 
>> I'd still appreciate any insight about whether importFrom in NAMESPACE
>> defers package loading so that if the package is not actually used (and is
>> not installed) there will be no problem.

I think that with importFrom(packagename, functioname), the package will
fail to INSTALL with message "object 'functioname' is not exported by
namespace:packagename'".

If the function is exported from packagname, then R CMD check will
complain that 'Namespace dependency not required: packagename', which is
to say that Imports: packagename is needed in the DESCRIPTION file.
Packages that are listed in the Imports field of DESCRIPTION must be
available at install time, so this implies that the user has packagename
installed.

I think this is trying to corral you to good programming practice: use
Imports: packagename in the DESCRIPTION, use importsFrom(packagename,
functioname) in the NAMESPACE, and only use functions that are exported
from packagename.

Martin

> 
> Imported packages need to be installed - but it's the import vs.
> suggests vs. depends statement in DESCRIPTION that controls this
> behaviour, not the namespace.
> 
> Hadley
> 
> 


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