[Rcpp-devel] type information about elements in Rcpp::List

Dirk Eddelbuettel edd at debian.org
Wed May 9 05:34:26 CEST 2012

On 8 May 2012 at 23:17, Jiqiang Guo wrote:
| Suppose I have a function in CPP as 
| void cppfun(Rcpp::List lst) {
|     ......
| }
| Then I would like to call this cppfun in R code as say 
| cppfun(list(a=a, b=b, c=c, ...)), in which 

(Well you need a SEXP somefun(SEXP ...) interface from R)

| a, b, c could be of different types and their type might be different as this 
| function gets called another time.  So I would like to know the type of a, b,
| c in the CPP code.  Could someone help me out or point to me some other 
| approaches?  Thanks.

It's a good question. I have at time thought about that a little, but have no
immediate solution for you.

One could possible use something C++-ish via traits.  

One could also use C level macros from the R API which simply test for types
as after all each element of a List must be a SEXP, so we use the SEXP-style

In the end I always went with more explicit code design: only use a List for
transfer to / from R, and otherwise use explicit C++ types.


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