fix(hesai_hw_interface): add error handling

.cspell.json

@@ -44,6 +44,9 @@
     "srvs",
     "manc",
     "ipaddr",
-    "ntoa"
+    "ntoa",
+    "piyushk",
+    "Piyush",
+    "fout"
   ]
 }

nebula_common/include/nebula_common/util/expected.hpp

@@ -0,0 +1,87 @@
+#pragma once
+
+#include <variant>
+
+namespace nebula
+{
+namespace util
+{
+
+struct bad_expected_access : public std::exception {
+  bad_expected_access(const std::string & msg) : std::exception(), msg_(msg) {}
+
+  const char* what() const noexcept override {
+    return msg_.c_str();
+  }
+
+private:
+  const std::string msg_; 
+};
+
+/// @brief A poor man's backport of C++23's std::expected.
+///
+/// At any given time, holds exactly one of: expected value, or error value.
+/// Provides functions for easy exception handling.
+///
+/// More info here: https://en.cppreference.com/w/cpp/utility/expected
+///
+/// @tparam T Type of the expected value
+/// @tparam E Error type
+template <typename T, typename E>
+struct expected
+{
+  /// @brief Whether the expected instance holds a value (as opposed to an error).
+  /// Call this before trying to access values via `value()`.
+  /// @return True if a value is contained, false if an error is contained
+  bool has_value() { return std::holds_alternative<T>(value_); }
+
+  /// @brief Retrieve the value, or throw `bad_expected_access` if an error is contained.
+  /// @return The value of type `T`
+  T value() {
+    if (!has_value()) {
+      throw bad_expected_access("value() called but containing error");
+    }
+    return std::get<T>(value_); 
+  }
+
+  /// @brief Return the contained value, or, if an error is contained, return the given `default_` instead.
+  /// @return The contained value, if any, else `default_`
+  T value_or(const T & default_)
+  {
+    if (has_value()) return value();
+    return default_;
+  }
+
+  /// @brief Return the contained value, or, if an error is contained, throw `runtime_error(error_msg)`.
+  /// @return The contained value if no error is thrown
+  T value_or_throw(const std::string & error_msg) {
+    if (has_value()) return value();
+    throw std::runtime_error(error_msg);
+  }
+
+  /// @brief Retrieve the error, or throw `bad_expected_access` if a value is contained.
+  /// @return The error of type `E`
+  E error() {
+    if (has_value()) {
+      throw bad_expected_access("error() called but containing value");
+    }
+    return std::get<E>(value_); 
+  }
+
+  /// @brief Return the contained error, or, if a value is contained, return the given `default_` instead.
+  /// @return The contained error, if any, else `default_`
+  E error_or(const E & default_) { 
+    if (!has_value()) return error();
+    return default_; 
+    }
+
+  expected(const T & value) { value_ = value; }
+
+  expected(const E & error) { value_ = error; }
+
+private:
+  std::variant<T, E> value_;
+};
+
+}  // namespace util
+}  // namespace nebula