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\name{cppFunction}
\alias{cppFunction}
\title{
Define an R Function with a C++ Implementation
}
\description{
Dynamically define an R function with C++ source code. Compiles and links a shared library with bindings to the C++ function then defines an R function that uses \code{.Call} to invoke the library.
}
\usage{
cppFunction(code, depends = character(), plugins = character(), includes = character(),
env = parent.frame(), rebuild = FALSE, cacheDir = getOption("rcpp.cache.dir",
tempdir()), showOutput = verbose, verbose = getOption("verbose"), echo = TRUE)
}
\arguments{
\item{code}{
Source code for the function definition.
}
\item{depends}{
Character vector of packages that the compilation depends on. Each package listed will first be queried for an \link[inline:plugins]{inline plugin} to determine header files to include. If no plugin is defined for the package then a header file based the package's name (e.g. \code{PkgName.h}) will be included.
}
\item{plugins}{
Character vector of \link[inline:plugins]{inline plugins} to use for the compilation.
}
\item{includes}{
Character vector of user includes (inserted after the includes provided by \code{depends}).
}
\item{env}{
The \link[base:environment]{environment} in which to define the R function. May be \code{NULL} in which case the defined function can be obtained from the return value of \code{cppFunction}.
}
\item{rebuild}{
Force a rebuild of the shared library.
}
\item{cacheDir}{
Directory to use for caching shared libraries. If the underlying code passed to \code{sourceCpp} has not changed since the last invocation then a cached version of the shared library is used. The default value of \code{tempdir()} results in the cache being valid only for the current R session. Pass an alternate directory to preserve the cache across R sessions.
}
\item{showOutput}{
\code{TRUE} to print \code{R CMD SHLIB} output to the console.
}
\item{verbose}{
\code{TRUE} to print detailed information about generated code to the console.
}
\item{echo}{
\code{TRUE} to silence output from optional R evaluation if set to \code{FALSE}.
}
}
\details{
Functions defined using \code{cppFunction} must have return types that are compatible with \code{Rcpp::wrap} and parameter types that are compatible with \code{Rcpp::as}.
The shared library will not be rebuilt if the underlying code has not changed since the last compilation.
}
\value{
An R function that uses \code{.Call} to invoke the underlying C++ function.
}
\note{
You can also define R functions with C++ implementations using the \code{\link{sourceCpp}} function, which allows you to separate the C++ code into it's own source file. For many use cases this is an easier and more maintainable approach.
}
\seealso{
\code{\link{sourceCpp}}, \code{\link{evalCpp}}
}
\examples{
\dontrun{
cppFunction(
'int fibonacci(const int x) {
if (x == 0) return(0);
if (x == 1) return(1);
return (fibonacci(x - 1)) + fibonacci(x - 2);
}')
cppFunction(depends = "RcppArmadillo",
'List fastLm(NumericVector yr, NumericMatrix Xr) {
int n = Xr.nrow(), k = Xr.ncol();
arma::mat X(Xr.begin(), n, k, false);
arma::colvec y(yr.begin(), yr.size(), false);
arma::colvec coef = arma::solve(X, y);
arma::colvec resid = y - X*coef;
double sig2 = arma::as_scalar(arma::trans(resid)*resid/(n-k) );
arma::colvec stderrest = arma::sqrt(
sig2 * arma::diagvec(arma::inv(arma::trans(X)*X)));
return List::create(Named("coefficients") = coef,
Named("stderr") = stderrest
);
}')
cppFunction(plugins=c("cpp11"), '
int useCpp11() {
auto x = 10;
return x;
}')
}
}
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