Le 16/11/2013 11:02, Romain Francois a écrit :
Hello,
I'm currently working on making Rcpp use the feature described here more:
http://cran.r-project.org/doc/manuals/R-exts.html#Linking-to-native-routines-in-other-packages
To give more context, Rcpp has for a long time built what we called "the
Rcpp user library", i.e. a library we could link against user the
linker. We were then producing appropriate linker flag with
Rcpp:::LdFlags(), ...
Now, I'm moving away from this and the intention is that a package using
Rcpp would only have to use
LinkingTo: Rcpp
This sets the -I flag as before to find headers from Rcpp, but this also
now takes advantage of what is described in writing R extensions:
http://cran.r-project.org/doc/manuals/R-exts.html#Linking-to-native-routines-in-other-packages
I'm doing this in a way that, when we are not compiling Rcpp, for
example the "type2name" function is defined in Rcpp's headers as an
inline function that grabs the registered function from Rcpp.
inline const char* type2name(SEXP x){
typedef const char* (*Fun)(SEXP) ;
static Fun fun = GET_(Fun) R_GetCCallable( "Rcpp", "type2name") ;
return fun(x) ;
}
This works great.
Now for the question. The documentation says:
"It must also specify ‘Imports’ or ‘Depends’ of those packages, for they
have to be loaded prior to this one (so the path to their compiled code
has been registered)."
Indeed if I don't have Depends or Imports, the R_init_Rcpp is not
called, and so the function is not registered.
But now if I do Depends: Rcpp or Imports: Rcpp for the sole purpose of
this LinkingTo mechanism, I'm getting
* checking dependencies in R code ... NOTE
Namespace in Imports field not imported from: ‘Rcpp’
All declared Imports should be used.
See the information on DESCRIPTION files in the chapter ‘Creating R
packages’ of the ‘Writing R Extensions’ manual.
It would be simple enough to require of our users that they have
Imports: Rcpp and import(Rcpp) or less in their NAMESPACE, but I was
wondering if we could make this more transparent, i.e. having LinkingTo:
Rcpp mean loading Rcpp.
I'm also curious about this sentence from the doc:
"In the future R may provide some automated tools to simplify exporting
larger numbers of routines."
Is there a draft of something ?
Romain
For details on how we will be using LinkingTo. Please see:
https://github.com/RcppCore/Rcpp/blob/master/inst/include/Rcpp/routines.h
where depending
- when we are compiling Rcpp, we just have a declaration of the
function, which is then defined in any of our .cpp files.
- when we are using Rcpp from another package, we are retrieving the
function
https://github.com/RcppCore/Rcpp/blob/master/src/Rcpp_init.cpp
where the functions are registered with the RCPP_REGISTER macro.
This way of using it moves all the logic to the package exposing its
functions. I find this nicer to use than other tactics I've seen, such
as the sub technique from Matrix ...
Typo alert. Of course here I meant the "stub" technique.
Romain
--
Romain Francois
Professional R Enthusiast
+33(0) 6 28 91 30 30
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