I'm writing an R package making use of Rcpp to call functions written in C++ into the R code. Some of these functions and templates are written in files with a .hpp extension following the convention used by boost (and also discussed here).
This does not result in an error when building (R CMD build .) and checking (R CMD check --as-cran package.tar.gz) the package, but it returns the next warning:
Subdirectory ‘src’ contains:
file.hpp example.hpp
These are unlikely file names for src files
Ok, this is not a big issue, but my concern is, why the warning? is naming *hpp files considered a bad practice in the R community? Are there objective or community reasons why I should use *cpp/*h files instead of *hpp for the templates?
I originally left this information as a comment, but realized it actually answers your question I think, so here goes:
As Dirk Eddelbuettel points out in the comments, when you have a question about an R Core Team policy on R extension packages, your best bet is to look through their excellent Writing R Extensions manual. This manual tells you almost anything you could ever need to know.
In your case specifically, you needed to look at Section 1.1.5, which explains that "[the R Core Team] recommend[s] using .h for headers" because (as they explain in footnote 18) "Using .hpp is not guaranteed to be portable."