[Rcpp-devel] Copying a NumericVector from a list within a list

[Krzysztof Sakrejda]

Sorry, accidental gmail send... here's what I meant:

On Sat, Apr 12, 2014 at 11:06 PM, Dirk Eddelbuettel <edd at debian.org> wrote:
> What can work as a single expression in R sometimes needs to be disentangled
> at the C++ level to help the compiler find its way through all the templates.
>
 [snip]
>
> // [[Rcpp::export]]
> NumericVector fromList(List outer, std::string name) {
>   List inner = outer[0];                // 0-based offsets in C++
>   return inner["p"];
> }

 I've noticed (I think...) having to do this sort of thing, but I want
 to ask a question to clarify: is it possible to have the above code
 work, but if you instead try:

 NumericVector fromList(List outer, std::string name) {
     return (outer[0])["p"];
 }

or even:

 NumericVector fromList(List outer, std::string name) {
     NumericVector vec = (outer[0])["p"];
     return vec;
 }

It will fail to compile?  That's what you mean by needing to "help the
compiler"?  If so,
is there some terminology for these sorts of problems?

Krzysztof