exercise-6-0.hpp

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// ===-- chapter-6/exercise-6-0.hpp ----------------------- -*- C++ -*- --=== //
#ifndef EXERCISE_6_0
#define EXERCISE_6_0
 
#include <boost/static_assert.hpp>
 
#include <boost/mpl/copy.hpp>
#include <boost/mpl/if.hpp>
#include <boost/mpl/placeholders.hpp>
#include <boost/mpl/vector.hpp>
using namespace boost::mpl::placeholders;
 
 
namespace exercise_6_0 {
 
struct no_type { };
 
template <typename T1, typename T2>
struct find_smaller
    : boost::mpl::if_<boost::mpl::bool_<(sizeof(T1) < sizeof(T2))>, T1, T2> { };
 
template <typename T2>
struct find_smaller<no_type, T2>
{
    typedef T2 type;
};
 
template <typename State = no_type, typename Operation = find_smaller<_, _> >
struct replace_with_smaller
{
    typedef Operation operation;
    typedef State state;
};
 
template <typename S>
struct smallest : boost::mpl::copy< S, replace_with_smaller<> > { };
 
} // namespace exercise_6_0
 
#endif // EXERCISE_6_0