[Rcpp-devel] Forcing a shallow versus deep copy

[Gabor Grothendieck]

On Thu, Jul 11, 2013 at 8:56 AM, Changi Han <changi.han.wen at gmail.com> wrote:
> 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.
>
>

It does suggest that many people are thinking along the same lines in
terms of new desirable features.

--
Statistics & Software Consulting
GKX Group, GKX Associates Inc.
tel: 1-877-GKX-GROUP
email: ggrothendieck at gmail.com