[Rcpp-devel] can one modify array in R memory from C++ without copying it?

[Dirk Eddelbuettel]

On 4 November 2011 at 08:28, romain at r-enthusiasts.com wrote:
| Not a bug, this is expected behaviour. 
| 
| If you pass a matrix of ints to the NumericVector ctor, Rcpp has no choice but to coerce the data to a matrix of double, which means new data, hence the original data does not get modified. 
| 
| If you pass a matrix of double, no copy is required, therefore Rcpp operates directly on the data. 
| 
| Those are features. 

And they are documented.

Dirk

 
| Le 4 nov. 2011 à 08:01, Darren Cook <darren at dcook.org> a écrit :
| 
| >> I.e. the point of his code was to show that a matrix of doubles gets
| >> modified, a matrix of ints does not.
| > 
| > Or change the first line from NumericMatrix to:
| >   Rcpp::IntegerMatrix r_m(mem);
| > 
| > Then the behaviour is reversed. The matrix of doubles does not get
| > modified, but the matrix of ints does!
| > 
| > Dirk, Romain, this is a bug-in-waiting. Is there any way to generate a
| > warning when the implicit deep copy happens? Or alternatively when the
| > pointer is being used implicitly... but my hunch is that I want to know
| > when there is any implicit conversion between int and double: modern C++
| > style is to explicitly declare all type conversions with static_cast<>
| > and friends.
| > 
| > Darren
| > _______________________________________________
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| > Rcpp-devel at lists.r-forge.r-project.org
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