It’s easy to create active bindings in R via makeActiveBinding(). This package faciliates the creation of active bindings that link back to C++ code. It provides an interface that allows binding several identifiers in an environment to the same C++ function, which is then called with the name (and a payload) as argument.

It is recommended to use the newer _wrapped functions that support passing an arbitrary Rcpp::List as payload. This allows to store an Rcpp::XPtr to a C++ object in that list. The XPtr then will be released when the payload is garbage-collected, and the C++ object will be destroyed.


You can install bindrcpp from github with:

# install.packages("devtools")


The following C++ module exports a function test_tolower_bindings() that creates active bindings that return the binding name in lowercase.

#include <Rcpp.h>

// [[Rcpp::depends(bindrcpp)]]
#include <bindrcpp.h>

#include <algorithm>
#include <string>

using namespace Rcpp;

using namespace bindrcpp;

SEXP tolower_callback(const String& name, PAYLOAD) {
  std::string name_string = name;
  std::transform(name_string.begin(), name_string.end(), name_string.begin(), ::tolower);
  return CharacterVector(name_string);

// [[Rcpp::export]]
SEXP test_tolower_bindings(CharacterVector names, Environment parent) {
  // We don't pass any payload here
  return bindrcpp::create_env_string(
    names, &tolower_callback, PAYLOAD(NULL), parent);

This function can be called from R:

env <- test_tolower_bindings(c("Converting", "to", "LOWERCASE"), .GlobalEnv)
#> [1] "Converting" "LOWERCASE"  "to"
#> [1] "converting"
#> [1] "to"
#> [1] "lowercase"

The bindings are read-only:

env$Converting <- "CONVERTING"
#> Error: Binding is read-only.