feat(core): Add ErrorCode template to standardize conversion of user-defined error code enums to std::error_code.

components/core/CMakeLists.txt

@@ -292,6 +292,7 @@ set(SOURCE_FILES_unitTest
         src/clp/DictionaryEntry.hpp
         src/clp/DictionaryReader.hpp
         src/clp/DictionaryWriter.hpp
+        src/clp/error_handling/ErrorCode.hpp
         src/clp/EncodedVariableInterpreter.cpp
         src/clp/EncodedVariableInterpreter.hpp
         src/clp/ErrorCode.hpp
@@ -459,6 +460,7 @@ set(SOURCE_FILES_unitTest
         tests/test-BufferedFileReader.cpp
         tests/test-EncodedVariableInterpreter.cpp
         tests/test-encoding_methods.cpp
+        tests/test-error_handling.cpp
         tests/test-ffi_SchemaTree.cpp
         tests/test-Grep.cpp
         tests/test-ir_encoding_methods.cpp

components/core/src/clp/error_handling/ErrorCode.hpp

@@ -0,0 +1,122 @@
+#ifndef CLP_ERROR_HANDLING_ERRORCODE_HPP
+#define CLP_ERROR_HANDLING_ERRORCODE_HPP
+
+#include <concepts>
+#include <string>
+#include <system_error>
+#include <type_traits>
+
+namespace clp::error_handling {
+/**
+ * Concept that defines a template parameter of an integer-based error code enumeration.
+ * @tparam Type
+ */
+template <typename Type>
+concept ErrorCodeEnumType = std::is_enum_v<Type> && requires(Type type) {
+    {
+        static_cast<std::underlying_type_t<Type>>(type)
+    } -> std::convertible_to<int>;
+};
+
+/**
+ * Template that defines a `std::error_category` of the given set of error code enumeration.
+ * @tparam ErrorCodeEnum
+ */
+template <ErrorCodeEnumType ErrorCodeEnum>
+class ErrorCategory : public std::error_category {
+public:
+    // Methods implementing `std::error_category`
+    /**
+     * Gets the error category name.
+     * Note: A specialization must be explicitly implemented for each valid `ErrorCodeEnum`.
+     * @return The name of the error category.
+     */
+    [[nodiscard]] auto name() const noexcept -> char const* override;
+
+    /**
+     * Gets the descriptive message associated with the given error.
+     * @param error_num
+     * @return The descriptive message for the error.
+     */
+    [[nodiscard]] auto message(int error_num) const -> std::string override;
+
+    // Methods
+    /**
+     * Gets the descriptive message associated with the given error.
+     * Note: A specialization must be explicitly implemented for each valid `ErrorCodeEnum`.
+     * @param error_enum.
+     * @return The descriptive message for the error.
+     */
+    [[nodiscard]] auto message(ErrorCodeEnum error_enum) const -> std::string;
+};
+
+/**
+ * Template class that defines an error code. An error code is represented by a error enum value and
+ * the associated error category. This template class is designed to be `std::error_code`
+ * compatible, meaning that every instance of this class can be used to construct a corresponded
+ * `std::error_code` instance, or compare with a `std::error_code` instance to inspect a specific
+ * error.
+ * @tparam ErrorCodeEnum
+ */
+template <ErrorCodeEnumType ErrorCodeEnum>
+class ErrorCode {
+public:
+    // Constructor
+    ErrorCode(ErrorCodeEnum error) : m_error{error} {}
+
+    /**
+     * @return The error code as an error number.
+     */
+    [[nodiscard]] auto get_errno() const -> int;
+
+    /**
+     * @return The underlying error code enum.
+     */
+    [[nodiscard]] auto get_err_enum() const -> ErrorCodeEnum;
+
+    /**
+     * @return The reference to the singleton of the corresponded error category.
+     */
+    [[nodiscard]] static auto get_category() -> ErrorCategory<ErrorCodeEnum> const&;
+
+private:
+    static inline ErrorCategory<ErrorCodeEnum> const cCategory;
+
+    ErrorCodeEnum m_error;
+};
+
+/**
+ * @tparam ErrorCodeEnum
+ * @param error
+ * @return Constructed `std::error_code` from the given `ErrorCode` instance.
+ */
+template <typename ErrorCodeEnum>
+[[nodiscard]] auto make_error_code(ErrorCode<ErrorCodeEnum> error) -> std::error_code;
+
+template <ErrorCodeEnumType ErrorCodeEnum>
+auto ErrorCategory<ErrorCodeEnum>::message(int error_num) const -> std::string {
+    return message(static_cast<ErrorCodeEnum>(error_num));
+}
+
+template <ErrorCodeEnumType ErrorCodeEnum>
+auto ErrorCode<ErrorCodeEnum>::get_errno() const -> int {
+    return static_cast<int>(m_error);
+}
+
+template <ErrorCodeEnumType ErrorCodeEnum>
+auto ErrorCode<ErrorCodeEnum>::get_err_enum() const -> ErrorCodeEnum {
+    return m_error;
+}
+
+template <ErrorCodeEnumType ErrorCodeEnum>
+auto ErrorCode<ErrorCodeEnum>::get_category() -> ErrorCategory<ErrorCodeEnum> const& {
+    return ErrorCode<ErrorCodeEnum>::cCategory;
+}
+
+template <typename ErrorCodeEnum>
+auto make_error_code(ErrorCode<ErrorCodeEnum> error) -> std::error_code {
+    return {error.get_errno(), ErrorCode<ErrorCodeEnum>::get_category()};
+}
+}  // namespace clp::error_handling
+
+#endif  // CLP_ERROR_HANDLING_ERRORCODE_HPP

components/core/tests/test-error_handling.cpp

@@ -0,0 +1,113 @@
+#include <cstdint>
+#include <string>
+#include <string_view>
+#include <system_error>
+#include <type_traits>
+
+#include <Catch2/single_include/catch2/catch.hpp>
+
+#include "../src/clp/error_handling/ErrorCode.hpp"
+
+using clp::error_handling::ErrorCategory;
+using clp::error_handling::ErrorCode;
+using std::string;
+using std::string_view;
+
+namespace {
+enum class AlwaysSuccessErrorCodeEnum : uint8_t {
+    Success = 0
+};
+
+enum class BinaryErrorCodeEnum : uint8_t {
+    Success = 0,
+    Failure
+};
+
+using AlwaysSuccessErrorCode = ErrorCode<AlwaysSuccessErrorCodeEnum>;
+using AlwaysSuccessErrorCategory = ErrorCategory<AlwaysSuccessErrorCodeEnum>;
+using BinaryErrorCode = ErrorCode<BinaryErrorCodeEnum>;
+using BinaryErrorCategory = ErrorCategory<BinaryErrorCodeEnum>;
+
+constexpr string_view cAlwaysSuccessErrorCategoryName{"Always Success Error Code"};
+constexpr string_view cBinaryTestErrorCategoryName{"Binary Error Code"};
+constexpr string_view cSuccessErrMsg{"Success"};
+constexpr string_view cFailureErrMsg{"Failure"};
+constexpr string_view cUnrecognizedErrorCode{"Unrecognized Error Code"};
+}  // namespace
+
+namespace std {
+template <>
+struct is_error_code_enum<BinaryErrorCode> : std::true_type {};
+
+template <>
+struct is_error_code_enum<AlwaysSuccessErrorCode> : std::true_type {};
+}  // namespace std
+
+template <>
+auto AlwaysSuccessErrorCategory::name() const noexcept -> char const* {
+    return cAlwaysSuccessErrorCategoryName.data();
+}
+
+template <>
+auto AlwaysSuccessErrorCategory::message(AlwaysSuccessErrorCodeEnum error_enum) const -> string {
+    switch (error_enum) {
+        case AlwaysSuccessErrorCodeEnum::Success:
+            return string{cSuccessErrMsg};
+        default:
+            return string{cUnrecognizedErrorCode};
+    }
+}
+
+template <>
+auto BinaryErrorCategory::name() const noexcept -> char const* {
+    return cBinaryTestErrorCategoryName.data();
+}
+
+template <>
+auto BinaryErrorCategory::message(BinaryErrorCodeEnum error_enum) const -> string {
+    switch (error_enum) {
+        case BinaryErrorCodeEnum::Success:
+            return string{cSuccessErrMsg};
+        case BinaryErrorCodeEnum::Failure:
+            return string{cFailureErrMsg};
+        default:
+            return string{cUnrecognizedErrorCode};
+    }
+}
+
+TEST_CASE("test_error_code_implementation", "[error_handling][ErrorCode]") {
+    // Test error codes within the same error category
+    BinaryErrorCode const success{BinaryErrorCodeEnum::Success};
+    std::error_code const success_error_code{success};
+    REQUIRE((success == success_error_code));
+    REQUIRE((cSuccessErrMsg == success_error_code.message()));
+    REQUIRE((BinaryErrorCode::get_category() == success_error_code.category()));
+    REQUIRE((cBinaryTestErrorCategoryName == success_error_code.category().name()));
+
+    BinaryErrorCode const failure{BinaryErrorCodeEnum::Failure};
+    std::error_code const failure_error_code{failure};
+    REQUIRE((failure == failure_error_code));
+    REQUIRE((cFailureErrMsg == failure_error_code.message()));
+    REQUIRE((BinaryErrorCode::get_category() == failure_error_code.category()));
+    REQUIRE((cBinaryTestErrorCategoryName == failure_error_code.category().name()));
+
+    REQUIRE((success_error_code != failure_error_code));
+    REQUIRE((success_error_code.category() == failure_error_code.category()));
+
+    AlwaysSuccessErrorCode const always_success{AlwaysSuccessErrorCodeEnum::Success};
+    std::error_code const always_success_error_code{always_success};
+    REQUIRE((always_success_error_code == always_success));
+    REQUIRE((cSuccessErrMsg == always_success_error_code.message()));
+    REQUIRE((AlwaysSuccessErrorCode::get_category() == always_success_error_code.category()));
+    REQUIRE((cAlwaysSuccessErrorCategoryName == always_success_error_code.category().name()));
+
+    // Compare error codes from different error category
+    // Error codes that have the same value or message won't be the same with each other if they are
+    // from different error categories.
+    REQUIRE((success_error_code.value() == always_success_error_code.value()));
+    REQUIRE((success_error_code.message() == always_success_error_code.message()));
+    REQUIRE((success_error_code.category() != always_success_error_code.category()));
+    REQUIRE((success_error_code != always_success_error_code));
+    REQUIRE((AlwaysSuccessErrorCode{AlwaysSuccessErrorCodeEnum::Success} != success_error_code));
+    REQUIRE((BinaryErrorCode{BinaryErrorCodeEnum::Success} != always_success_error_code));
+}