welcome error codes

develop/singles/headers/meta.hpp/meta_all.hpp

@@ -27,6 +27,7 @@
 #include <span>
 #include <string>
 #include <string_view>
+#include <system_error>
 #include <tuple>
 #include <type_traits>
 #include <utility>
@@ -307,23 +308,100 @@ namespace meta_hpp::detail
 #    define META_HPP_TRY try
 #    define META_HPP_CATCH(...) catch ( __VA_ARGS__ )
 #    define META_HPP_RETHROW() throw
-#    define META_HPP_THROW(...) throw ::meta_hpp::detail::exception(__VA_ARGS__)
 #else
 #    define META_HPP_TRY if ( true )
 #    define META_HPP_CATCH(...) if ( false )
 #    define META_HPP_RETHROW() std::abort()
-#    define META_HPP_THROW(...) std::abort()
 #endif
 
 namespace meta_hpp::detail
 {
-#if !defined(META_HPP_NO_EXCEPTIONS)
-    class exception final : public std::runtime_error {
-    public:
-        explicit exception(const char* what)
-        : std::runtime_error(what) {}
+    enum class generic_error {
+        no_error,
+        bad_uvalue_cast,
+        bad_argument_cast,
+        bad_instance_cast,
     };
+
+    class generic_error_category final : public std::error_category {
+    public:
+        ~generic_error_category() override = default;
+
+        generic_error_category(generic_error_category&&) = delete;
+        generic_error_category(const generic_error_category&) = delete;
+
+        generic_error_category& operator=(generic_error_category&&) = delete;
+        generic_error_category& operator=(const generic_error_category&) = delete;
+
+        [[nodiscard]] const char* name() const noexcept override {
+            return "generic";
+        }
+
+        [[nodiscard]] std::string message(int ev) const override {
+            switch ( static_cast<generic_error>(ev) ) {
+            case generic_error::no_error:
+                return "no error";
+            case generic_error::bad_uvalue_cast:
+                return "bad uvalue cast";
+            case generic_error::bad_argument_cast:
+                return "bad argument cast";
+            case generic_error::bad_instance_cast:
+                return "bad instance cast";
+            }
+            return "unexpected error code";
+        }
+
+        static const std::error_category& instance() noexcept {
+            static const generic_error_category instance;
+            return instance;
+        }
+
+    private:
+        generic_error_category() = default;
+    };
+}
+
+namespace std
+{
+    template <>
+    struct is_error_code_enum<meta_hpp::detail::generic_error> : true_type {};
+}
+
+namespace meta_hpp::detail
+{
+    inline std::error_code make_error_code(generic_error err) noexcept {
+        static_assert(std::is_same_v<int, std::underlying_type_t<generic_error>>);
+        return std::error_code{static_cast<int>(err), generic_error_category::instance()};
+    }
+}
+
+namespace meta_hpp::detail
+{
+    class generic_exception final : public std::logic_error {
+    public:
+        explicit generic_exception(generic_error err)
+        : generic_exception{make_error_code(err)} {}
+
+        explicit generic_exception(std::error_code ec)
+        : std::logic_error(ec.message())
+        , error_code_{ec} {}
+
+        [[nodiscard]] const std::error_code& code() const noexcept {
+            return error_code_;
+        }
+
+    private:
+        std::error_code error_code_{};
+    };
+
+    [[noreturn]] inline void throw_generic_exception(generic_error err) {
+#if !defined(META_HPP_NO_EXCEPTIONS)
+        throw generic_exception{err};
+#else
+        (void)err;
+        std::abort();
 #endif
+    }
 }
 
 namespace meta_hpp::detail
@@ -1333,9 +1411,8 @@ namespace meta_hpp::detail
 
 namespace meta_hpp
 {
-#if !defined(META_HPP_NO_EXCEPTIONS)
-    using detail::exception;
-#endif
+    using detail::generic_error;
+    using detail::generic_exception;
 
     using detail::hashed_string;
     using detail::memory_buffer;
@@ -5558,7 +5635,7 @@ namespace meta_hpp::detail
             }
         }
 
-        META_HPP_THROW("bad argument cast");
+        throw_generic_exception(generic_error::bad_argument_cast);
     }
 
     template < typename To >
@@ -5614,7 +5691,7 @@ namespace meta_hpp::detail
             }
         }
 
-        META_HPP_THROW("bad argument cast");
+        throw_generic_exception(generic_error::bad_argument_cast);
     }
 }
 
@@ -6068,7 +6145,7 @@ namespace meta_hpp::detail
             }
         }
 
-        META_HPP_THROW("bad instance cast");
+        throw_generic_exception(generic_error::bad_instance_cast);
     }
 }
 
@@ -8675,7 +8752,7 @@ namespace meta_hpp
             }
         }
 
-        META_HPP_THROW("bad value cast");
+        throw_generic_exception(generic_error::bad_uvalue_cast);
     }
 
     template < typename T >
@@ -8692,7 +8769,7 @@ namespace meta_hpp
             }
         }
 
-        META_HPP_THROW("bad value cast");
+        throw_generic_exception(generic_error::bad_uvalue_cast);
     }
 
     template < typename T >
@@ -8709,7 +8786,7 @@ namespace meta_hpp
             }
         }
 
-        META_HPP_THROW("bad value cast");
+        throw_generic_exception(generic_error::bad_uvalue_cast);
     }
 
     template < typename T >