r - Access "natural coercion" logic from C/C++ code -

when calling unlist or c, type promoted smallest type capable of representing everything:

> c(as.integer(1), 2.3, '3') [1] "1"   "2.3" "3"   > c(true, 5) [1] 1 5 > unlist(list(as.integer(1:5), as.complex(2:4))) [1] 1+0i 2+0i 3+0i 4+0i 5+0i 2+0i 3+0i 4+0i 

how can access logic c/c++ code?

i have looked c sources of c , unlist , found following code in both do_c_dflt , do_unlist (main/bind.c):

if (data.ans_flags & 512)      mode = exprsxp; else if (data.ans_flags & 256) mode = vecsxp; else if (data.ans_flags & 128) mode = strsxp; else if (data.ans_flags &  64) mode = cplxsxp; else if (data.ans_flags &  32) mode = realsxp; else if (data.ans_flags &  16) mode = intsxp; else if (data.ans_flags &   2) mode = lglsxp; else if (data.ans_flags &   1) mode = rawsxp; 

the variable data, of type binddata, computed routine answertype seems define coercion logic. however, type binddata declared in bind.c only.

so: r's general coercion logic exported anywhere, or bound copy-paste code bind.c? (sorry pun...)

kevin posted an article on rcpp gallery pretty close in spirit, tests explicitly using macros r's api:

#include <rcpp.h> using namespace rcpp;  // [[rcpp::export]] list do_stuff( list x_ ) {     list x = clone(x_);     for( list::iterator = x.begin(); != x.end(); ++it ) {         switch( typeof(*it) ) {             case realsxp: {                 numericvector tmp = as<numericvector>(*it);                 tmp = tmp * 2;                 break;                 }             case intsxp: {                 if( rf_isfactor(*it) ) break; // factors have type intsxp                 integervector tmp = as<integervector>(*it);                 tmp = tmp + 1;                 break;             }             default: {                 stop("incompatible sexp encountered;");             }        }   }     return x; }