Function copy

test/base-test.cc:39–42

using testing::Return;

auto copy(fmt::string_view s, fmt::appender out) -> fmt::appender {
  for (char c : s) *out++ = c;
  return out;
}

TEST(string_view_test, value_type) {
  static_assert(std::is_same<fmt::string_view::value_type, char>::value, "");