#include <utility>
template <typename T> void swap(T& a, T& b)
{
  T c(std::move(a)); a=std::move(b); b=std::move(c);
}
template <class T, std::size_t N> void swap(T (&a)[N], T (&b)[N])
{
  for (std::size_t i = 0; i<N; ++i) swap(a[i],b[i]);
}
// C++98 version was
//{
//  T c(a); a=b; b=c;
//}