#include <boost/variant.hpp>
#include <QTime>

struct Null{};

typedef boost::make_recursive_variant
    < Null
    , std::pair< int, boost::recursive_variant_ >
    >::type IntList;

const IntList ilNull = IntList( Null( ) );

void ilPushFront1( IntList & il, int i )
{
    il = IntList( std::make_pair( i, il ) );
}
void ilPushFront2( IntList & il, int i )
{
    IntList il2 = IntList( std::make_pair( i, ilNull ) );
    boost::get<std::pair<int,IntList> >( il2 ).second.swap( il );
    il.swap( il2 );
}
int main()
{
    QTime t;
    t.start();

    IntList il = ilNull;
    for( int i = 0; i < 1000; ++i )
        ilPushFront1( il, i );
    std::cout << "unoptimized ilPushFront: " << t.restart() << std::endl;
    for( int i = 0; i < 1000; ++i )
        ilPushFront1( il, i );
    std::cout << "unoptimized ilPushFront w/ larger list: " << t.restart() << std::endl;

    IntList il2 = ilNull;
    for( int i = 0; i < 1000; ++i )
        ilPushFront2( il2, i );
    std::cout << "optimized ilPushFront: " << t.restart() << std::endl;
    for( int i = 0; i < 1000; ++i )
        ilPushFront2( il2, i );
    std::cout << "optimized ilPushFront w/ larger list: " << t.restart() << std::endl;

};