Class AttributeTrail

eval/eval/attribute_trail.h:22–60

AttributeTrail reflects current attribute path. It is functionally similar to cel::Attribute, yet intended to have better complexity on attribute path increment operations. TODO(issues/41) Current AttributeTrail implementation is equivalent to cel::Attribute - improve it. Intended to be used in conjunction with cel::Value, describing the attribute value originated from. Empty AttributeTrail denote

// Empty AttributeTrail denotes object with attribute path not defined
// or supported.
class AttributeTrail {
 public:
  AttributeTrail() : attribute_(absl::nullopt) {}

  explicit AttributeTrail(std::string variable_name)
      : attribute_(absl::in_place, std::move(variable_name)) {}

  explicit AttributeTrail(cel::Attribute attribute)
      : attribute_(std::move(attribute)) {}

  // NOLINTNEXTLINE(google-explicit-constructor)
  AttributeTrail(absl::nullopt_t) : AttributeTrail() {}

  AttributeTrail(const AttributeTrail&) = default;
  AttributeTrail& operator=(const AttributeTrail&) = default;
  AttributeTrail(AttributeTrail&&) = default;
  AttributeTrail& operator=(AttributeTrail&&) = default;

  AttributeTrail& operator=(absl::nullopt_t) {
    attribute_.reset();
    return *this;
  }

  // Creates AttributeTrail with attribute path incremented by "qualifier".
  AttributeTrail Step(cel::AttributeQualifier qualifier) const;

  // Creates AttributeTrail with attribute path incremented by "qualifier".
  AttributeTrail Step(const std::string* qualifier) const {
    return Step(cel::AttributeQualifier::OfString(*qualifier));
  }

  // Returns CelAttribute that corresponds to content of AttributeTrail.
  const cel::Attribute& attribute() const { return attribute_.value(); }

  bool empty() const { return !attribute_.has_value(); }

 private:
  absl::optional<cel::Attribute> attribute_;
};

}  // namespace google::api::expr::runtime