Class string

12.19-constevalParmCheck1/main.cpp:12–89

#if not(__cpp_lib_constexpr_string > 201911)
class string {
public:
  constexpr string() = default;
  constexpr string(const char& c) { append(&c, 1); }
  constexpr string(const string& s) { append(s.data(), s.size()); }
  constexpr string& operator=(const string& s)
  {
    reset();
    append(s.data(), s.size());
    return *this;
  }

  constexpr string(string&& s) noexcept
  : _data{std::exchange(s._data, nullptr)}
  , _length{s._length}
  {}

  constexpr string& operator=(string&& s) noexcept
  {
    std::exchange(_data, s._data);
    _length = s._length;
    return *this;
  }

  // a regular std::string is convertible to a string_view or better
  // there is a string_view ctor for a std::string. Make that work
  constexpr operator std::string_view() const noexcept
  {
    return {_data, _length};
  }

  constexpr string(std::string_view d) { append(d.data(), d.size()); }
  constexpr ~string() noexcept { reset(); }

  constexpr string& append(std::string_view d)
  {
    return append(d.data(), d.size());
  }
  constexpr string& append(const string& s)
  {
    return append(s.data(), s.size());
  }
  constexpr string& append(const char* d, std::size_t len)
  {
    const std::size_t needNt{(len && (d[len - 1] != '\0')) ? 1u : 0u};

    char* tmp = new char[_length + len + needNt]{};
    std::copy_n(_data, _length, tmp);
    std::copy_n(d, len, tmp + _length);
    _length += len;

    delete[] _data;

    _data = tmp;

    return *this;
  }