c++20/exercise-2-2.hpp

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// ===-- chapter-2/c++20/exercise-2-2.hpp ----------------- -*- C++ -*- --=== //
#ifndef EXERCISE_2_2
#define EXERCISE_2_2
 
#include <assert.h>
#include <memory>
#include <type_traits>
 
 
namespace exercise_2_2 {
 
inline namespace cpp20 {
 
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)
{
    static_assert(std::is_reference<Target>::value);
 
    // NOTE: If a Source defines operator&, this can lead to undesired results.
    assert(
        dynamic_cast<
            typename std::add_pointer<
                typename std::remove_reference<Target>::type
            >::type>(std::addressof(x))
        == std::addressof(x));
    return static_cast<Target>(x);
}
 
} // inline namespace cpp20
} // namespace exercise_2_2
 
#endif // EXERCISE_2_2