Hello,
I think I (superficially) understand the difference between:
// [[Rcpp::export]]
double sum1(Rcpp::NumericMatrix M) {
arma::mat A(M.begin(), M.rows(), M.cols(), false);
return sum(sum(A));
}
// [[Rcpp::export]]
double sum2(arma::mat A) {
return sum(sum(A));
}
Partly out of laziness, partly because sum2 is more elegant, and partly to
avoid namespace pollution, I was wondering if there is a way to "force" a
"shallow" copy in sum2.
If not, then may I submit a low priority feature request. An attribute?
Some thing like:
// [[Rcpp::export]]
double sum2(arma::mat A) {
// [[ Rcpp::shallow ( A ) ]]
return sum(sum(A));
}
Or (akin to C++11 generalized attributes)
// [[Rcpp::export]] { [[ Rcpp::shallow ( A ) ]] }
double sum2(arma::mat A) {
return sum(sum(A));
}
An alternative is to have an argument in sourceCpp that takes a list/vector
of objects that are to be shallow or deep copied.
For example in sum1, if M is changed within the function before casting to
the arma::mat, then might be cleaner to add M to a list/vector of objects
to be deep copied rather than cloning M within sum1: leads to one fewer
variable name.
Just a thought. I can certainly live with the additional step. As always,
thanks for all the Rcpp goodness.
Cheers,
Changi Han
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