create list with more than 20 elements (different syntax)

gistfile1.cpp

#include <Rcpp.h>
using namespace Rcpp ;

template <typename T>
inline void set_item_impl( List& target, int i, const T& obj, CharacterVector& names, traits::true_type ){
    target[i] = obj.object ;
    names[i] = obj.name ;
}

template <typename T>
inline void set_item_impl( List& target, int i, const T& obj, CharacterVector&, traits::false_type ){
    target[i] = obj ;
}

template <typename T>
inline void set_item( List& target, int i, const T& obj, CharacterVector& names){
    set_item_impl( target, i, obj, names, typename traits::is_named<T>::type() ) ;
}

class SequentialInserter{
public:
    SequentialInserter( List& target_, CharacterVector& names_ ) : target(target_), names(names_), index(0){}
       
    class SequentialInserterProxy{
    public:
        SequentialInserterProxy( SequentialInserter& parent_, const char* name_ ) : parent(parent_), name(name_){}
        
        template <typename T>
        void operator=( const T& obj){
            parent.set( name, obj ) ;
        }  
        
    private:
        SequentialInserter& parent ;
        const char* name ;
    } ;
    
    inline SequentialInserterProxy operator[]( const char* name){
        return SequentialInserterProxy( *this, name );    
    }
    
    template <typename T>
    void set( const char* name, const T& obj){
        target[index] = obj ;
        names[index] = name ;
        index++ ;
    }
      
private:
    List& target ;
    CharacterVector& names;
    int index ;
    
} ;

// [[Rcpp::export]]
List biglist(){
    List out( 30 ) ; CharacterVector names(30) ;  
    SequentialInserter inserter( out, names );
    
    inserter["x0"]  = 42  ;
    inserter["x1"]  = 42  ;
    inserter["x2"]  = 42  ;
    inserter["x3"]  = 42  ;
    inserter["x4"]  = 42  ;
    inserter["x5"]  = 42  ;
    inserter["x6"]  = 42  ;
    inserter["x7"]  = 42  ;
    inserter["x8"]  = 42  ;
    inserter["x9"]  = 42  ;
    inserter["x10"] = 42  ;
    inserter["x11"] = 42  ;
    inserter["x12"] = 42  ;
    inserter["x13"] = 42  ;
    inserter["x14"] = 42  ;
    inserter["x15"] = 42  ;
    inserter["x16"] = 42  ;
    inserter["x17"] = 42  ;
    inserter["x18"] = 42  ;
    inserter["x19"] = 42  ;
    inserter["x20"] = 42  ;
    inserter["x21"] = 42  ;
    inserter["x22"] = 42  ;
    inserter["x23"] = 42  ;
    inserter["x24"] = 42  ;
    inserter["x25"] = 42  ;
    inserter["x26"] = 42  ;
    inserter["x27"] = 42  ;
    inserter["x28"] = 42  ;
    inserter["x29"] = 42  ;
    out.names() = names ;
    return out ;
}

/*** R
   biglist()
*/