[Rd] Using requireNamespace() instead of require()

[Prof Brian Ripley]

On 28/09/2014 14:09, Duncan Murdoch wrote:
> On 28/09/2014, 8:47 AM, Viechtbauer Wolfgang (STAT) wrote:
>> Suppose I have a function funcA() in package pkgA that requires function funcB() from another package pkgB under certain circumstances. Those circumstances are rare though, so I put package pkgB under 'Suggests', and use this in funcA() when those circumstances do arise:
>>
>> if (require("pkgB", quietly=TRUE)) {
>>     pkgB::funcB(...)
>> } else {
>>     stop("Please install package 'pkgB' to do this.")
>> }
>>
>> I understand that using requireNamespace() would be preferable and I would also prefer to do that. But funcB() depends on funcC() from pkgC that it lists under 'Depends'. So, with require("pkgB"), both namespaces (of pkgB and pkgC) are loaded and attached to the search list and things run. But with requireNamespace("pkgB"), only the namespace of pkgB is loaded, so funcC() can't be found. So, I figured, I also use requireNamespace("pkgC"), but that's not sufficient, since funcB() calls funcC() and not pkgC::funcC().
>>
>> Is there any solution to this?
>
> The solution needs to be implemented by the maintainer of pkgB.  It
> probably doesn't really need pkgC on the search list, and could be
> modified to import funcC or explicitly call pkgC::funcC.
>
> If you aren't the maintainer of pkgB, and the real maintainer is
> unresponsive, then you're stuck using require().

I was writing something very similar, but added

'If the maintainer of pkgB does not respond you probably do not want to 
rely on his work, not least because repository admins also will not get 
a response from him.'

>
> Duncan Murdoch


-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Emeritus Professor of Applied Statistics, University of Oxford
1 South Parks Road, Oxford OX1 3TG, UK