These __are__ similar. The difference is in the classes themselves.
Rcpp classes are proxy classes so C++ copy mechanism does not apply to
them. arma classes are proper c++ classes, so C++ semantics apply.
I'm at useR right now, so I can't really work on this. I'll submit at
least ideas later.
Romain
Le 2013-07-11 15:34, Changi Han a écrit :
I am sure there are better ways to achieve the goal. I would suggest
that these two be similar if possible. I think the naive expectation
is for them to be consistent.
// [[Rcpp::export]]
stuff function(Rcpp::stuff) {
}
// [[Rcpp::export]]
stuff function(arma::stuff) {
}
Thank you again. Cheers.
On Thu, Jul 11, 2013 at 9:22 PM, <rom...@r-enthusiasts.com [3]>
wrote:
Hello,
This comes up every now and then, I think we can find a syntax to
initiate an arma::mat that would allow what you want.
It is not likely it will come via attributes. The idea is to keep
them simple. The solutions I see below would eventually lead to
clutter, and we are heading in the less clutter direction.
Ill think about it and propose something.
Romain
Le 2013-07-11 14:32, Changi Han a écrit :
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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