The Rcpp package provides C++ classes that greatly facilitate
interfacing C or C++ code in R packages using the .Call() interface
provided by R.

Rcpp provides matching C++ classes for a large number of basic R
data types. Hence, a package author can keep his data in normal R
data structures without having to worry about translation or
transferring to C++. At the same time, the data structures can be
accessed as easily at the C++ level, and used in the normal manner.

The mapping of data types works in both directions. It is as
straightforward to pass data from R to C++, as it is it return data
from C++ to R.

WWW: https://cran.r-project.org/web/packages/Rcpp/