boost mpl manipulating a vector

Consider the following code copied from Polukhin:

	#include <iostream>
	#include <boost/mpl/size.hpp>
	#include <boost/type_traits/is_same.hpp>
	#include <boost/static_assert.hpp>
	#include <boost/mpl/if.hpp>
	#include <boost/type_traits/make_unsigned.hpp>
	#include <boost/type_traits/add_const.hpp>
	#include <boost/mpl/transform.hpp>
	#include <boost/mpl/vector.hpp>
	#include <boost/mpl/at.hpp>
	// Make unsigned
	struct unsigne; // No typo: 'unsigned' is a keyword, we cannot use it.
	// Make constant
	struct constant;
	// Otherwise we do not change type
	struct no_change;
	template <class Types, class Modifiers>
	struct do_modifications
	{
	BOOST_STATIC_ASSERT((boost::is_same<
	typename boost::mpl::size<Types>::type,
	typename boost::mpl::size<Modifiers>::type
	>::value));
	typedef boost::mpl::if_<
	boost::is_same<boost::mpl::_2, unsigne>,
	boost::make_unsigned<boost::mpl::_1>,
	boost::mpl::if_<
	boost::is_same<boost::mpl::_2, constant>,
	boost::add_const<boost::mpl::_1>,
	boost::mpl::_1
	>
	> binary_operator_t;
	typedef typename boost::mpl::transform<
	Types,
	Modifiers,
	binary_operator_t
	>::type type;
	};
	typedef boost::mpl::vector<unsigne, no_change, constant, unsigne> modifiers;
	typedef boost::mpl::vector<int, char, short, long> types;
	typedef do_modifications<types, modifiers>::type result_type;
	BOOST_STATIC_ASSERT((boost::is_same<
	boost::mpl::at_c<result_type, 0>::type,
	unsigned int
	>::value));
	BOOST_STATIC_ASSERT((boost::is_same<
	boost::mpl::at_c<result_type, 1>::type,
	char
	>::value));
	BOOST_STATIC_ASSERT((boost::is_same<
	boost::mpl::at_c<result_type, 2>::type,
	const short
	>::value));
	BOOST_STATIC_ASSERT((boost::is_same<
	boost::mpl::at_c<result_type, 3>::type,
	unsigned long
	>::value));
	int main(int argc, char *argv[])
	{
	auto x = 78;
	std::cout << "Hello World! " << x << std::endl;
	return 0;
	}

view raw main.cpp hosted with ❤ by GitHub

When run, this code simply prints "Hello World! 78"