Brian,
Prof Brian Ripley <mailto:ripley at stats.ox.ac.uk> wrote:
This is one of those undocumented things (AFAIK): LENGTH applies only to 'vectors'. So don't use t and definitely don't set it for others. The macro expands to #define LENGTH(x) (((VECSEXP) (x))->vecsxp.length) What is a vector here? Something which gets actually allocated by allocVector() AFAICS, that is an atomic or generic vector or an expression. OTOH, an EXTPTRSXP is stored in a cons cell. There is also a function length(), which is safer.
Thanks for your message. Things are much clearer now to me. Can I safely assume that INTSXP, REALSXP, LGLSXP, STRSXP, CPLXSXP and VECSXP are vectors (while EXTPTRSXP is not). Thomas