Dear all, I am re-posting this question to Rcpp-devel on suggestion on the R-help list. Sorry for this cross-posting.
I experience a problem in implementing a S4 class in a package and would appreciate your help in this matter. The class is implemented using Rcpp and works well. I am now trying to extend the class with R functions, adding them as methods with a call to setMethod(...). When I do this outside the package (after loading the package with "library(...)"), everything works smoothly. However, when I try to incorporate the call to setMethod(...) in the package code itself, the only way I get it to work is to include the call in .onLoad(...) or .onAttach(...). This works, but when loading the library I get the messages "creating new generic function for "plot" in ".GlobalEnv", as well as "no definition for class "Rcpp_rothC""... Again, the code works, but the messages let me presume that I add the methods in the wrong way or miss-specify name spaces, class names, or something else. It has been suggested that the Rcpp class might have to be encapsulated into a second S4 class ( http://r.789695.n4.nabble.com/Problem-with-quot-setMethod-quot-in-R-package-tt3238061.html), but this would be a bit unfortunate since all C++ - fields and methods would have to be "passed through" via extra code. Or did I miss something? I'd appreciate your advice before re-organising this code. Pascal (The error message and the relevant parts of the package files are pasted below, together with my related questions as "comments".) showMethods("plot") Function "plot": <not a generic function> # I am surprised about this -- # why isn't plot a generic function? library("RrothC2") Loading required package: Rcpp Loading required package: pascal Creating a new generic function for "plot" in ".GlobalEnv" in method for ‘plot’ with signature ‘x="Rcpp_rothC",y="missing"’: no definition for class "Rcpp_rothC" # class seems not to be known # at this stage. # but where should I put setMethod()? r1 <- new(rothC$rothC); class(r1) # class is known by now [1] "Rcpp_rothC" attr(,"package") [1] ".GlobalEnv" plot(r1) # "plot" is dispatched correctly showMethods("plot") Function: plot (package graphics) # now "plot" from graphics shows up x="ANY", y="ANY" # why was it missing before? x="Rcpp_rothC", y="missing" ######### FILE rcpp_rothC_module.h ######### class rothC { ... } ######### FILE rcpp_rothC_module.cpp ######### using namespace Rcpp ; RCPP_MODULE(rothC) { class_<rothC>("rothC") .constructor() ... } ######### FILE rcpp_rothC.R ######### Rcpp_rothC.plot <- function(x,y,...) { ... } ########## FILE zzz.R ########## .NAMESPACE <- environment() rothC <- new( "Module" ) .onLoad <- function(libname, pkgname) { unlockBinding( "rothC" , .NAMESPACE ) assign( "rothC", Module( "rothC" ), .NAMESPACE ) setMethod(f="plot",signature(x="Rcpp_rothC",y="missing"),definition=Rcpp_rothC.plot,where=.GlobalEnv); lockBinding( "rothC", .NAMESPACE ) } .onAttach <- function(libname, pkgname) {} .onUnload <- function(libname, pkgname) { gc(); }
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