Hi,
I was recently hunting down a bug in my code, and stumbled upon a slightly
incoherent behaviour in Rcpp/RcppArmadillo. In my real application I have a
class which data members are initialized in initialization list from the Rcpp
List using as<arma::cube>. For example, I have a member y which I initialize by
y(as<arma::cube>(xlist["y"])). This caused some headaches if I later modified
data member y, as the y in the list on R side was modified as well. I then
realized that I need to use Rcpp::clone in order to make a deep copy of xlist
object. But, this does not need to be done when initializing arma::vec or
arma::mat. Is this purposeful or am I missing something?
Simple example:
void test1(const NumericVector& x) {
arma::cube ycube(as<arma::cube>(x));
ycube(0) = 0.5;
}
> y <- array(1:4, c(2,2,1)) #y is integer type, using automatic copy
> test1(y)
> y
, , 1
[,1] [,2]
[1,] 1 3
[2,] 2 4
> y <- array(as.numeric(1:4), c(2,2,1)) #y is numeric, no copy
> test1(y)
> y
, , 1
[,1] [,2]
[1,] 0.5 3
[2,] 2.0 4
But in case of arma::vec (or arma::mat), copying is always done:
void test2(const NumericVector& x) {
arma::vec yvec(as<arma::vec>(x));
yvec(0) = 0.5;
}
> y <- as.numeric(1:8)
> test2(y)
> y
[1] 1 2 3 4 5 6 7 8
Best regards,
Jouni Helske
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