Method swap

Bcore/src/main/cpp/Dobby/tests/catch.hpp:9585–9589

}

void StringRef::swap(StringRef &other) noexcept {
  std::swap(m_start, other.m_start);
  std::swap(m_size, other.m_size);
  std::swap(m_data, other.m_data);
}

auto StringRef::c_str() const -> char const * {
  if (isSubstring())