On 17 April 2018 at 15:09, Serguei Sokol wrote:
| Hi,
|
| I would like to re-discuss the subject of automatic coercion of
| NULL to some vector in function parameter list. This old topic was
| already raised e.g. here
| https://stackoverflow.com/questions/34718570/rcpp-pass-vector-of-length-0-null-to-cppfunction
|
| To resume, actually a function defined as (ivec is from RcppArmadillo package)
|
| sourceCpp(code="
| // [[Rcpp::depends(RcppArmadillo)]]
| #include <RcppArmadillo.h>
| using namespace arma;
| // [[Rcpp::export]]
| ivec f(ivec x) {return x+1;}
| ")
|
| and called as f(c()) will produce an error:
| Error in f(c()) :
| Not compatible with requested type: [type=NULL; target=integer].
|
| What I propose is (for this example) to mimic a call f(integer(0)) which gives:
| > f(integer(0))
| [,1]
|
| The following one-line patch would do the job:
| diff --git a/inst/include/Rcpp/r_cast.h b/inst/include/Rcpp/r_cast.h
| index e59fa799..c0ec0817 100644
| --- a/inst/include/Rcpp/r_cast.h
| +++ b/inst/include/Rcpp/r_cast.h
| @@ -63,6 +63,7 @@ namespace Rcpp {
| case LGLSXP:
| case CPLXSXP:
| case INTSXP:
| + case NILSXP:
| return Rf_coerceVector(x, RTYPE);
| default:
| const char* fmt = "Not compatible with requested type: "
|
| It will automatically coerce NULL to a declared vector type.
| It's a more primitive solution than Nullable<T> but in many cases
| it can be largely sufficient and make code look shorter and clearer.
|
| Will it break something in established usage habits? Is it compatible with your plans for Rcpp?
| I can prepare a PR if you decide to include it.
We could test that. It may not do harm -- so I just turned on a rev.dep
check for it.
Can you open an issue for it on GH though? Better visibility and easier 'per
concrete topic' discussion.
Dirk
--
http://dirk.eddelbuettel.com | @eddelbuettel | edd at debian.org