exercise-2-0.hpp

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// ===-- chapter-2/exercise-2-0.hpp ----------------------- -*- C++ -*- --=== //
#ifndef EXERCISE_2_0
#define EXERCISE_2_0
 
#include <boost/type_traits/add_const.hpp>
#include <boost/type_traits/add_reference.hpp>
 
 
namespace exercise_2_0 {
 
namespace no_boost {
 
template <typename T, bool IsRef>
struct add_const_ref_impl
{
    typedef T const& type;
};
template <typename T>
struct add_const_ref_impl<T, true>
{
    typedef T type;
};
 
template <typename T>
struct add_const_ref : add_const_ref_impl<T, false> { };
 
template <typename T>
struct add_const_ref<T&> : add_const_ref_impl<T&, true> { };
 
template <typename T>
struct add_const_ref<T const> : add_const_ref_impl<T, false> { };
 
} // namespace no_boost
 
 
namespace with_boost {
 
template <typename T>
struct add_const_ref
{
    // For int&, add_const has no effect, then add_reference does nothing as
    // it's already a reference type.
    typedef typename boost::add_reference<
        typename boost::add_const<T>::type
    >::type type;
};
 
} // with_boost
 
template<typename T>
struct add_const_ref : no_boost::add_const_ref<T> { };
 
} // namespace exercise_2_0
 
#endif // EXERCISE_2_0