Thanks for the reply. The solution of requiring the namespace from within Rcpp hadn't occurred to me.
I had used Environment::namespace_env("pkg_name") before, but I think the problem here is that lazy-loaded (and maybe other elements we expect in R) are not available if this is done from Rcpp. E.g. # (using R --vanilla) Rcpp::cppFunction('Rcpp::Environment getUnloaded2() { return Rcpp::Environment::namespace_env("nycflights13"); }') ls(envir = getUnloaded2()) # empty, whereas the following: nycflights13::flights # pulls the data, with the package not being loaded or attached. To close this thread, I think what the latter command does differently to Rcpp is to load the package, because sessionInfo() after running the second command, includes nycflights13 in the section "loaded via a namespace (and not attached):" This is not the case after pulling the environment into an Rcpp variable. Thanks again for steering me, Jack On 04/15/2018 10:18 PM, Kevin Ushey wrote: > The environments called 'package:foo' are associated with attached packages; > that is, they're located on the search path. You likely want to find the > actual package namespace. > > I think we have a static function Environment::namespace_env() for this. Or > you can just call back to R with requireNamespace(). > > Kevin > > On Fri, Apr 13, 2018 at 10:10 PM, Wasey, Jack O <j...@jackwasey.com > <mailto:j...@jackwasey.com>> wrote: > > Dear all, > > It seems I can reference lazy-loaded data from an unloaded, unattached > package from R, but not using the equivalent Rcpp as described in the > quickref document. I checked out: > http://dirk.eddelbuettel.com/code/rcpp/html/Environment_8h_source.html > <http://dirk.eddelbuettel.com/code/rcpp/html/Environment_8h_source.html> and > even the scant references to environments in the C API section of "Writing R > Extensions" and doesn't see what I'm missing. I suspect this is a limitation > of R's C interface, not necessarily Rcpp itself. > > I use the package nycflights13 as an example. Running `sessionInfo()` > shows the package nycflights13 is not loaded, then I run: > R --vanilla > > a <- nycflights13::flights > > Which completes without error. In Rcpp, I cannot even get a handle on the > package namespace if it is not loaded. > > Rcpp::cppFunction('Rcpp::Environment getUnloaded() { Rcpp::Environment > env("package:nycflights13"); return env;}') > getUnloaded() > Error in getUnloaded() : > Cannot convert object to an environment: [type=character; > target=ENVSXP]. > > library(nycflights13) > Rcpp::cppFunction('Rcpp::Environment getUnloaded() { Rcpp::Environment > env("package:nycflights13"); return env;}') > getUnloaded() > <environment: package:nycflights13> > attr(,"name") > [1] "package:nycflights13" > attr(,"path") > [1] > "/Library/Frameworks/R.framework/Versions/3.4/Resources/library/nycflights13" > > > > I also found that simple using `loadNamespace` was insufficient for the > Rcpp approach to work, but after `library` or `attachNamespace` the above > function does work. > > Am I treading in another rare code path? All I want to do is use a > lazy-loaded data set in an Rcpp function when the package may not be loaded > when called. Should I just be passing it as a parameter to the function? This > seems ugly. > > Using Rcpp 0.12.16, R 3.4.3 on Mac. > > Any advice appreciated. Thanks, > > Jack > > > _______________________________________________ > Rcpp-devel mailing list > Rcpp-devel@lists.r-forge.r-project.org > <mailto:Rcpp-devel@lists.r-forge.r-project.org> > https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel > <https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel> > > _______________________________________________ Rcpp-devel mailing list Rcpp-devel@lists.r-forge.r-project.org https://lists.r-forge.r-project.org/cgi-bin/mailman/listinfo/rcpp-devel