[Rcpp-devel] Forcing a shallow versus deep copy

[Changi Han]

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 <ggrothendieck at gmail.com
> wrote:

> On Thu, Jul 11, 2013 at 8:32 AM, Changi Han <changi.han.wen at 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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