[Rcpp-devel] How do I load a rcpp module?

[Glenn Lawyer]

Dear Steve,

Thanks for a quick answer. Please see comments inline, below.

On 03/12/2012 10:54 AM, Steve Lianoglou wrote:
> You can try to load the shared library once you `R CMD
> SHLIB` it using `dyn.load` (see ?dyn.load).
Yes, you can try this, but the example in the vingette does not 
include this step. The vingette has only
 >require(Rcpp)
 >mod <- Module("mod").

Which fails.

I would then guess, as you did, that I should load the compiled 
code, and that dyn.load is the proper command. Except this also fails:
 > require(Rcpp)
Loading required package: Rcpp
 > dyn.load("test.so")
 > mod <- Module("mod")
 > mod$norm(3,4)
Error in Module(module, mustStart = TRUE) :
   Failed to initialize module pointer: Error in 
FUN("_rcpp_module_boot_mod"[[1L]], ...): no such symbol 
_rcpp_module_boot_mod in package .GlobalEnv

So I check the help text on dyn.load. Perhaps I need to load my 
shared library into the global env?

 > dyn.load("test.so",local=FALSE)
 > mod <- Module("mod")
 > mod$norm(3,4)
Error in Module(module, mustStart = TRUE) :
   Failed to initialize module pointer: Error in 
FUN("_rcpp_module_boot_mod"[[1L]], ...): no such symbol 
_rcpp_module_boot_mod in package .GlobalEnv

fails.

>> This is, in fact, my main frustration with all of the rcpp documentation. It
>> consistently assumes a high level of sophistication from its users. Almost
>> none of the examples work "as is", nor do they give hints as to what
>> information is missing.
> I don't know how fair of a complaint that is ... at a minimum, I think
> you should be familiar with the concepts in the "Writing R Extensions"
> manual:
>
> http://cran.r-project.org/doc/manuals/R-exts.pdf
>
> and I don't think it's really unfair for the devs to assume that as a
> starting point.

Rcpp is a vast improvement over the older approach to writing R 
extensions, a point the developers are rightly proud of. Given 
that, it is inconsistent to expect intimately familiarity with the 
(now) obsolete approach in order to get even the most basic 
examples of the new approach to work.

A vingette in which /none/ of the examples work as written makes a 
very frustrating introduction to a topic, and one I would hesitate 
to pass on to my students.

+glenn



On 03/12/2012 10:54 AM, Steve Lianoglou wrote:
> Hi Glenn,
>
> On Mon, Mar 12, 2012 at 5:26 AM, Glenn Lawyer<lawyer at mpi-inf.mpg.de>  wrote:
>> Dear List,
>>
>> I am working through the vingette "Exposing C++ functions and classes with
>> Rcpp modules," and am stuck at section 2.2.1.
>>
>> I create a text file with the code for the Uniform class, and successfully
>> compile it with R CMD SHLIB.
>>
>> Can you please tell me how to load it into R so that I can continue with the
>> example? The vingette clearly shows how to use it once everything is set up,
>> but does not show how to set things up.
> I suspect they want you to either whip the functionality you are using
> to create a module from into a package of sorts (some documentation
> for that is at the end of the vignette, but also in other (non
> Module-specific) Rcpp vignettes).
>
> You can alternatively try to load the shared library once you `R CMD
> SHLIB` it using `dyn.load` (see ?dyn.load). You will definitely need
> to have Rcpp loaded in your workspace first, though.
>
> That may or may not work w/ modules, though ... I never tried, but:
>
>> This is, in fact, my main frustration with all of the rcpp documentation. It
>> consistently assumes a high level of sophistication from its users. Almost
>> none of the examples work "as is", nor do they give hints as to what
>> information is missing.
> I don't know how fair of a complaint that is ... at a minimum, I think
> you should be familiar with the concepts in the "Writing R Extensions"
> manual:
>
> http://cran.r-project.org/doc/manuals/R-exts.pdf
>
> and I don't think it's really unfair for the devs to assume that as a
> starting point.
>
> I guess you're somehow right in the sense that reading through that
> requires a bit of R sophistication, but what you're trying to do w/
> Rcpp is sophisticated :-)
>
> Also, the examples using `inline` are the ones you can get away with
> doing w/o having some R know-how, but once you get into the world of
> trying to compile external C++ code and include it "seamlessly" into
> R, you really should do a bit of h/w on the R library/package building
> process (the R-exts doc above).
>
> Hope that helps,
> -steve
>

-- 
-----------------------------------
It is difficult to find a black cat in a dark room,
especially if there is no cat.
   -- Chinese proverb

   Dr. Glenn Lawyer
   +352 661 967 244
   Max-Planck-Institut für Informatik
   Computational Biology and Applied Algorithmics
   Campus E1 4
   66123 Saarbrücken, Germany
   http://bioinf.mpi-inf.mpg.de/~lawyer


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