add: [imp] error_code

include/libimp/error.h

@@ -0,0 +1,68 @@
+/**
+ * @file libimp/error.h
+ * @author mutouyun (orz@orzz.org)
+ * @brief A platform-dependent error code.
+ * @date 2022-12-18
+ */
+#pragma once
+
+#include <string>
+
+#include "libimp/def.h"
+#include "libimp/export.h"
+#include "libimp/result.h"
+#include "libimp/fmt_cpo.h"
+
+LIBIMP_NAMESPACE_BEG_
+
+/**
+ * @brief Serves as the base class for specific error category types.
+ * @see https://en.cppreference.com/w/cpp/error/error_category
+ */
+class LIBIMP_EXPORT error_category {
+public:
+  error_category(error_category const &) = delete;
+  error_category &operator=(error_category const &) = delete;
+
+  constexpr error_category() noexcept = default;
+  virtual ~error_category() noexcept = default;
+
+  /// @brief observer
+  virtual std::string message(result_code r) const = 0;
+
+  /// @brief comparison function
+  bool operator==(error_category const &rhs) const noexcept;
+};
+
+/**
+ * @brief Identifies the generic error category.
+ * @see https://en.cppreference.com/w/cpp/error/generic_category
+ */
+LIBIMP_EXPORT error_category const &generic_category() noexcept;
+
+/**
+ * @brief The error code object.
+ * @see https://en.cppreference.com/w/cpp/error/error_code
+ */
+class LIBIMP_EXPORT error_code {
+  result_code r_code_;
+  error_category const *ec_;
+
+public:
+  /// @brief constructors
+  error_code() noexcept;
+  error_code(result_code r, error_category const &ec) noexcept;
+
+  /// @brief observers
+  result_code code() const noexcept;
+  result_type value() const noexcept;
+  error_category const &category() const noexcept;
+  std::string message() const;
+  explicit operator bool() const noexcept;
+
+  /// @brief comparison functions
+  friend LIBIMP_EXPORT bool operator==(error_code const &lhs, error_code const &rhs) noexcept;
+  friend LIBIMP_EXPORT bool operator!=(error_code const &lhs, error_code const &rhs) noexcept;
+};
+
+LIBIMP_NAMESPACE_END_

src/libimp/error.cpp

@@ -0,0 +1,62 @@
+#include <typeinfo>
+
+#include "libimp/error.h"
+#include "libimp/fmt.h"
+
+LIBIMP_NAMESPACE_BEG_
+
+bool error_category::operator==(error_category const &rhs) const noexcept {
+  return typeid(*this) == typeid(rhs);
+}
+
+namespace {
+
+class generic_error_category : public error_category {
+public:
+  std::string message(result_code r) const {
+    return fmt("[", r.value(), (!r ? ", \"success\"]" : ", \"failure\"]"));
+  }
+};
+
+} // namespace
+
+error_category const &generic_category() noexcept {
+  static generic_error_category ec;
+  return ec;
+}
+
+error_code::error_code() noexcept
+  : r_code_{}, ec_{&generic_category()} {}
+
+error_code::error_code(result_code r, error_category const &ec) noexcept
+  : r_code_{r}, ec_{&ec} {}
+
+result_code error_code::code() const noexcept {
+  return r_code_;
+}
+
+result_type error_code::value() const noexcept {
+  return r_code_.value();
+}
+
+error_category const &error_code::category() const noexcept {
+  return *ec_;
+}
+
+std::string error_code::message() const {
+  return ec_->message(r_code_);
+}
+
+error_code::operator bool() const noexcept {
+  return !!r_code_;
+}
+
+bool operator==(error_code const &lhs, error_code const &rhs) noexcept {
+  return (lhs.r_code_ == rhs.r_code_) && (*lhs.ec_ == *rhs.ec_);
+}
+
+bool operator!=(error_code const &lhs, error_code const &rhs) noexcept {
+  return !(lhs == rhs);
+}
+
+LIBIMP_NAMESPACE_END_

test/imp/test_imp_error.cpp

@@ -0,0 +1,31 @@
+#include <iostream>
+
+#include "gtest/gtest.h"
+
+#include "libimp/error.h"
+#include "libimp/result.h"
+#include "libimp/fmt.h"
+
+namespace {
+
+class custom_error_category : public imp::error_category {
+public:
+  std::string message(imp::result_code r) const {
+    return !r ? "success" : "failure";
+  }
+};
+
+} // namespace
+
+TEST(error, error_code) {
+  imp::error_code ecode;
+  EXPECT_FALSE(ecode);
+  std::cout << ecode.message() << "\n";
+  EXPECT_EQ(ecode.message(), "[0, \"success\"]");
+
+  custom_error_category cec;
+  ecode = {123, cec};
+  EXPECT_TRUE(ecode);
+  std::cout << ecode.message() << "\n";
+  EXPECT_EQ(ecode.message(), cec.message(123));
+}