I entirely missed that thread ... sorry. I came across the above examples at:
http://lists.r-forge.r-project.org/pipermail/rcpp-devel/2013-April/005680.html On Thu, Jul 11, 2013 at 8:38 PM, Gabor Grothendieck <ggrothendi...@gmail.com > wrote: > On Thu, Jul 11, 2013 at 8:32 AM, Changi Han <changi.han....@gmail.com> > wrote: > > 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. > > I had just made a similar suggestion in my post about half an hour ago. >
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