R devel - Oct 2010 - Sections 5.8.1 and 5.8.2 of Writing R Extensions (LinkingTo)

Hello,

In Sections 5.8.1 and 5.8.2 of Writing R Extensions the following pattern is
suggested
for getting the path to a file in another package:

PKGB_PATH=‘echo ’library(packB); cat(system.file("libs",
package="packB"))’
\
| ${R_HOME}/bin/R --vanilla --slave‘

Is the library(packB) really needed here? It is not needed on two systems
that
I have tested: Windows and Linux. What about MacOS?

If loading packB requires loading many other packages or doing expensive
initialization it would be much more efficient if we could omit
library(packB)
here.

On the other hand, keeping library(packB) has one possible advantage,
namely,
it may eliminate the need to add packB.dll to the loader's search path. So
there
is a trade-off of convenience vs efficiency.

Thanks,
Dominick

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On Oct 27, 2010, at 1:22 PM, Dominick Samperi wrote:
> Hello,
> 
> In Sections 5.8.1 and 5.8.2 of Writing R Extensions the following pattern
is
> suggested
> for getting the path to a file in another package:
> 
> PKGB_PATH=?echo ?library(packB); cat(system.file("libs",
package="packB"))?
> \
> | ${R_HOME}/bin/R --vanilla --slave?
> 
> Is the library(packB) really needed here?
Not that I'm aware of - it's just a check that that package can be used.
If you omit it you will get an empty string and no error on failure.

> It is not needed on two systems
> that
> I have tested: Windows and Linux. What about MacOS?
> 
> If loading packB requires loading many other packages or doing expensive
> initialization it would be much more efficient if we could omit
> library(packB)
> here.
> 
> On the other hand, keeping library(packB) has one possible advantage,
> namely,
> it may eliminate the need to add packB.dll to the loader's search path.
Not really since that sub-process will die when finished so it won't have
any effect on any search path.


BTW: system.file("libs",...)  doesn't do the job these days since
it will be missing R_ARCH so you need something like
system.file("libs",.Platform$r_arch, package=...)
for any more recent R.

Cheers,
Simon

> So
> there
> is a trade-off of convenience vs efficiency.
> 
> Thanks,
> Dominick
> 
> 	[[alternative HTML version deleted]]
> 
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