RcppHoney Introduction

// [[Rcpp::depends(RcppHoney)]]

#include <RcppCommon.h>
#include <RcppHoneyForward.hpp> // we have to do this because we're going to hook in a non-default structure
#include <list>

// We have to declare our hooks before we include RcppHoney.hpp
namespace RcppHoney {
namespace hooks {

// Hook in all std::list types (could be more specific)
template< typename T, typename A >
traits::true_type is_hooked(const std::list< T, A > &val);

// Tell RcppHoney that NA has meaning in std::list
template< typename T, typename A >
traits::true_type has_na(const std::list< T, A > &val);

// Tell RcppHoney that it needs to create basic (e.g. std::list + std::list) operators
template< typename T, typename A >
traits::true_type needs_basic_operators(const std::list< T, A > &val);

// Tell RcppHoney that it needs to create scalar (e.g. std::list + int/double) operators
template< typename T, typename A >
traits::true_type needs_scalar_operators(const std::list< T, A > &val);

// Tell RcppHoney that this set of types is part of the FAMILY_USER + 1 family.
// This is used in conjunction with needs_basic_operators.  If you have
// needs_basic_operators return RcppHoney::traits::false_type, then only types
// that are not part of the same family will have binary operators created
// between them.
template< typename T, typename A >
traits::int_constant< FAMILY_USER + 1 > family(const std::list< T, A > &val);

} // namespace hooks
} // namespace RcppHoney

#include <RcppHoney.hpp>

// [[Rcpp::export]]
Rcpp::NumericVector example_manually_hooked() {

    // We manually hooked std::list in to RcppHoney so we'll create one
    std::list< int > l;
    l.push_back(1); l.push_back(2); l.push_back(3); l.push_back(4); l.push_back(5);

    // std::vector is already hooked in to RcppHoney in default_hooks.hpp so we'll
    // create one of those too
    std::vector< int > v(l.begin(), l.end());

    // And for good measure, let's create an Rcpp::NumericVector which is also hooked by default
    Rcpp::NumericVector v2(v.begin(), v.end());

    // Now do some weird operations incorporating std::vector, std::list, Rcpp::NumericVector
    // and some RcppHoney functions and return it.  The return value will be equal to the following
    // R snippet:
    //     v <- 1:5
    //     result <- 42 + v + v + log(v) - v - v + sqrt(v) + -v + 42

    // We can store our result in any of RcppHoney::LogicalVector, RcppHoney::IntegerVector, or
    // RcppHoney::NumericVector and simply return it to R.  These classes inherit from their
    // Rcpp counterparts and add a new constructor.  The only copy of the data, in this case, is when
    // we assign our expression to retval.  Since it is then a "native" R type, returning it is a
    // shallow copy.  Alternatively we could write this as:
    //     return Rcpp::wrap(1 + v + RcppHoney::log(v) - v - 1 + RcppHoney::sqrt(v) + -v2);

    RcppHoney::NumericVector retval
        =  42 + l + v + RcppHoney::log(v) - v - l + RcppHoney::sqrt(v) + -v2 + 42;
    return retval;
}