More easily, you can use Rcpp::Reference:
// [[Rcpp::export]]
std::string getId(Reference obj) {
std::string txt = obj.field("id");
return txt;
}
Here, you are isolated from the implementation of reference classes
using environments and the .xData slot name.
Romain
Le 29/05/13 01:49, Dirk Eddelbuettel a écrit :
On 28 May 2013 at 23:14, Anwar Ludin wrote:
| Hello,
|
| I have a Reference class defined in R that I am passing as a parameter
| to a C++ class using Rcpp. I am trying to access the fields of the
| Reference class from C++ and I'm not sure how to do this.
Well for starters your reference class object had no field price so that
makes extracting it hard...
But in essence: a) reference classes are S4 objects, and as b) you can see
from str() and unclass(), they contain an environment you can access. So try
this modification of your code:
library(Rcpp)
library(methods)
Instrument <-setRefClass(
Class="Instrument",
fields=list("id"="character", "description"="character")
)
Instrument$accessors(c("id", "description"))
instrument <- Instrument$new(id="AAPL", description="Apple")
cat("Instrument:\n")
print(instrument)
#print(str(instrument))
cat("\n\nInstrument unclassed:\n")
print(unclass(instrument))
cat("\n\nInstrument .xData env.:\n")
print(ls(instrument@.xData))
cppFunction('
std::string getId(S4 obj) {
// get the environment
Environment e = obj.slot(".xData");
// extract field
std::string txt = as<std::string>(e["id"]);
// return it
return txt;
}')
cat("\n\nId extracted from instrument:\n")
print(getId(instrument))
Hope this helps, Dirk
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