In looking through the Rcpp/0.11.3 code, I came across this file:
inst/include/Rcpp/vector/instantiation.h
The file contains the declarations for IntegerVector, NumericVector, etc. It
seems reasonable to assume that these types will be used in basically any code
using Rcpp.
The declarations are aliases to templates. For example:
typedef Vector<REALSXP> NumericVector ;
The effect of this is that every .cpp file declaring a NumericVector must
recompile the template, because these declarations rely on implicit
instantiation. However, from the perspective of an Rcpp user, these types are
actually not templates. In other words, there is no NumericVector<T> template
providing compile-time polymorphism, and NumericVector is a fully-specified
type. The implicit instantiation increases both compile time and object file
size ("code bloat") for packages using Rcpp. As such, I'd suggest that these
types should be provided pre-compiled in the Rcpp dynamic object, which can be
done via explicit template instantiation
(http://en.cppreference.com/w/cpp/language/class_template).
I've put a modified instantation.h at
https://gist.github.com/5180d60689fa8d6cb353.git and the corresponding (and
incomplete) .cpp file at https://gist.github.com/c13135659e0b27421a3a.git.
This implementation should result in a situation where the object code for
these types is present only once on a user's system, rather than being
replicated once per package that is using Rcpp.
While I appreciate that Rcpp is "header-only", I think that the current
declaration of these types is better-served with compiled code, for the reasons
mentioned above. However, I may be missing something--perhaps there is
something about the way dynamic objects in R do things that means this approach
would not work?
___________________________
Kevin Thornton
Associate Professor
Ecology and Evolutionary Biology
University of California, Irvine
http://www.molpopgen.org
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