Hello,
This is an implementation artefact. In short, you are not supposed to
use [[.
Romain
Le 22/10/12 10:54, North, Ben a écrit :
Hi,
I recently came across some behaviour of `[[` and `$` which surprised
me. I was trying to access a method of a class implemented using Rcpp,
choosing the method name at runtime, but the example below uses a fixed
method name to keep it short.
The full C++ code:
- - - - 8< - - - -
#include <Rcpp.h>
struct Constant
{
Constant(double x) : x(x) {}
double value() const { return x; }
const double x;
};
RCPP_MODULE(Constant)
{
Rcpp::class_<Constant>("Constant")
.constructor<double>()
.method("value", &Constant::value);
}
- - - - 8< - - - -
and the R script with (summarised) results embedded as comments:
- - - - 8< - - - -
## Versions:
## R 2.15.1
## Rcpp 0.9.14
require(methods)
require(Rcpp)
dll.info <- dyn.load("Constant")
mod <- Module("Constant", dll.info, mustStart = TRUE)
Constant <- mod$Constant
x <- new(Constant, 2.2)
x[["value"]]
## NULL
x$value
## Class method definition for method value()
## [...]
x[["value"]]
## Class method definition for method value()
## [...]
- - - - 8< - - - -
The fact that 'x[["value"]]' finds the method only if I've first done
'x$value' seemed odd.
Thanks,
Ben.
--
Romain Francois
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