Expected str_to_bool()

in folly/Conv.cpp [268:338]

• 68 lines of code
• 27 McCabe index (conditional complexity)

Expected<bool, ConversionCode> str_to_bool(StringPiece* src) noexcept {
  auto b = src->begin(), e = src->end();
  for (;; ++b) {
    if (b >= e) {
      return makeUnexpected(ConversionCode::EMPTY_INPUT_STRING);
    }
    if (!std::isspace(*b)) {
      break;
    }
  }

  bool result;
  auto len = size_t(e - b);
  switch (*b) {
    case '0':
    case '1': {
      result = false;
      for (; b < e && isdigit(*b); ++b) {
        if (result || (*b != '0' && *b != '1')) {
          return makeUnexpected(ConversionCode::BOOL_OVERFLOW);
        }
        result = (*b == '1');
      }
      break;
    }
    case 'y':
    case 'Y':
      result = true;
      if (!bool_str_cmp(&b, len, "yes")) {
        ++b; // accept the single 'y' character
      }
      break;
    case 'n':
    case 'N':
      result = false;
      if (!bool_str_cmp(&b, len, "no")) {
        ++b;
      }
      break;
    case 't':
    case 'T':
      result = true;
      if (!bool_str_cmp(&b, len, "true")) {
        ++b;
      }
      break;
    case 'f':
    case 'F':
      result = false;
      if (!bool_str_cmp(&b, len, "false")) {
        ++b;
      }
      break;
    case 'o':
    case 'O':
      if (bool_str_cmp(&b, len, "on")) {
        result = true;
      } else if (bool_str_cmp(&b, len, "off")) {
        result = false;
      } else {
        return makeUnexpected(ConversionCode::BOOL_INVALID_VALUE);
      }
      break;
    default:
      return makeUnexpected(ConversionCode::BOOL_INVALID_VALUE);
  }

  src->assign(b, e);

  return result;
}