Example of R Reference Classes + Rcpp Attributes

convolve.cpp

#include <Rcpp.h>
using Rcpp::NumericVector;

// [[Rcpp::export]]
void convolveCpp(const NumericVector a, const NumericVector b, NumericVector xab) {
	int na = a.size(), nb = b.size();
	if ( (na + nb-1) != xab.size() ) {
		Rcpp::Rcout << "ab.size: " << na+nb << ", xab.size: " << xab.size() << std::endl;
		Rcpp::stop("Dimension mismatch in convolveCpp");
	};
	// zero-out
	xab.fill(0);
	// convolve
	for (int i = 0; i < na; i++) {
		for (int j = 0; j < nb; j++) {
			xab[i + j] += a[i] * b[j];
		}
	}
}

Convolver.R

library(Rcpp)
sourceCpp('convolve.cpp')

Convolver <- setRefClass("Convolver",
	fields = list(
		data = "numeric", 
		answer = "numeric"
	),
	methods = list(
		convolve = function(x) {
			dim_new <- length(x)+length(data)-1
			## only re-alloc if necessary
			if (length(answer) != dim_new) {
				cat('## Realloc answer\n')
				answer <<- numeric(dim_new)
			}
			convolveCpp(data, x, answer)
			cat(c('Answer: ', round(answer,3), '\n'))
		}
	)
)

kernel1 <- c(1,3,1)/5
kernel2 <- c(2,1,2)/5
dat <- c(1:5, 0, 5:1)

the_test <- Convolver$new(data=dat/sum(dat))
the_test$convolve(kernel1)
the_test$convolve(kernel2)

In R, run with:

source("Convolver.cpp")

source("Convolver.R")
(not ".cpp")?