One of the more amusing aspects of Rcpp is just how spectacularly bad my design for the (original) Date and Datetime vector (and scalar !) types was. (In my defense, I knew little R and was driven by what QuantLib did with std::vector.) I did a first cleanup a decade (give or take) ago, but given the (not needed, really) scalar classes I omitted default constructors for zero length vectors.

R 4.5.0 now behaves differently for zero-length vectors. It shows less tolerance, and bonks out more clearly. This became apparent this week in issue #135 in anytime where I now (in a branch for now, release "soon") cover the case of construction from integer() or numeric(). But this lead to some introspection here too (ahem!!) and I sketched in two simple default constructors which seem to work. As this simply expands the API surface I do not expect trouble.