exercise-2-2.hpp

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// ===-- chapter-2/exercise-2-2.hpp ----------------------- -*- C++ -*- --=== //
#ifndef EXERCISE_2_2
#define EXERCISE_2_2
 
#include <boost/static_assert.hpp>
#include <boost/type_traits/add_pointer.hpp>
#include <boost/type_traits/is_reference.hpp>
#include <boost/type_traits/remove_reference.hpp>
 
#include <assert.h>
 
 
namespace exercise_2_2 {
 
template <typename Target, typename Source>
inline Target polymorphic_downcast(Source *const x)
{
    assert(dynamic_cast<Target>(x) == x);
    return static_cast<Target>(x);
}
 
template <typename Target, typename Source>
inline Target polymorphic_downcast(Source& x)
{
    BOOST_STATIC_ASSERT((boost::is_reference<Target>::value));
 
    // NOTE: If a Source defines operator&, this can lead to undesired results.
    assert(
        dynamic_cast<
            typename boost::add_pointer<
                typename boost::remove_reference<Target>::type
            >::type>(&x)
        == &x);
    return static_cast<Target>(x);
}
 
} // namespace exercise_2_2
 
#endif // EXERCISE_2_2