template<typename OutputIterator, typename ConstInputIterator>
static OutputIterator copy(OutputIterator s1, ConstInputIterator s2, std::size_t n);
#include <sprout/string.hpp>
#include <sprout/assert.hpp>
using namespace sprout;
auto x = string<8>("homuhomu");;
SPROUT_STATIC_CONSTEXPR auto y = string<8>("madocchi");
char_traits<char>::copy(x.begin(), y.begin(), 8);
SPROUT_ASSERT_MSG(x[0] == y[0], "y is copied to x.");