typesafe.h

// Copyright (C) 2016 Jonathan Müller <[email protected]>
// This file is subject to the license terms in the LICENSE file
// found in the top-level directory of this distribution.

#define TYPE_SAFE_ENABLE_ASSERTIONS 0 // disable assertions

//=== assertions boilerplate ===//
//======================================================================//
// Copyright (C) 2016 Jonathan Müller <[email protected]>
// 
// This software is provided 'as-is', without any express or
// implied warranty. In no event will the authors be held
// liable for any damages arising from the use of this software.
//
// Permission is granted to anyone to use this software for any purpose,
// including commercial applications, and to alter it and redistribute
// it freely, subject to the following restrictions:
// 
// 1. The origin of this software must not be misrepresented;
//    you must not claim that you wrote the original software.
//    If you use this software in a product, an acknowledgment
//    in the product documentation would be appreciated but
//    is not required.
// 
// 2. Altered source versions must be plainly marked as such,
//    and must not be misrepresented as being the original software.
// 
// 3. This notice may not be removed or altered from any
//    source distribution.
//======================================================================//

#ifndef DEBUG_ASSERT_HPP_INCLUDED
#define DEBUG_ASSERT_HPP_INCLUDED

#include <cstdlib>

#ifndef DEBUG_ASSERT_NO_STDIO
    #include <cstdio>
#endif

#ifndef DEBUG_ASSERT_MARK_UNREACHABLE
    #ifdef __GNUC__
        #define DEBUG_ASSERT_MARK_UNREACHABLE __builtin_unreachable()
    #elif defined(_MSC_VER)
        #define DEBUG_ASSERT_MARK_UNREACHABLE __assume(0)
    #else
        /// Hint to the compiler that a code branch is unreachable.
        /// Define it yourself prior to including the header to override it.
        #define DEBUG_ASSERT_MARK_UNREACHABLE
    #endif
#endif

#ifndef DEBUG_ASSERT_ASSUME
    #ifdef __GNUC__
        #define DEBUG_ASSERT_ASSUME(Expr) do { if (!(Expr)) __builtin_unreachable(); } while (0)
    #elif defined(_MSC_VER)
        #define DEBUG_ASSERT_ASSUME(Expr) __assume(Expr)
    #else
        /// Hint to the compiler that a condition is `true`.
        /// Define it yourself prior to including the header to override it.
        #define DEBUG_ASSERT_ASSUME(Expr)
    #endif
#endif

#ifndef DEBUG_ASSERT_FORCE_INLINE
    #ifdef __GNUC__
        #define DEBUG_ASSERT_FORCE_INLINE [[gnu::always_inline]] inline
    #elif defined(_MSC_VER)
        #define DEBUG_ASSERT_FORCE_INLINE __forceinline
    #else
        /// Strong hint to the compiler to inline a function.
        /// Define it yourself prior to including the header to override it.
        #define DEBUG_ASSERT_FORCE_INLINE inline 
    #endif
#endif

namespace debug_assert
{
    //=== source location ===//
    /// Defines a location in the source code.
    struct source_location
    {
        const char* file_name; ///< The file name.
        unsigned line_number; ///< The line number.
        const char* function_name; ///< The function name.
    };

    /// Expands to the current [debug_assert::source_location]().
    #define DEBUG_ASSERT_CUR_SOURCE_LOCATION debug_assert::source_location{__FILE__, __LINE__, __func__}

    //=== level ===//
    /// Tag type to indicate the level of an assertion.
    template <unsigned Level>
    struct level {};

    /// Helper class that sets a certain level.
    /// Inherit from it in your module handler.
    template <unsigned Level>
    struct set_level
    {
        static const unsigned level = Level;
    };

    template <unsigned Level>
    const unsigned set_level<Level>::level;

    //=== handler ===//
    /// Does not do anything to handle a failed assertion (except calling [std::abort()]()).
    /// Inherit from it in your module handler.
    struct no_handler
    {
        /// \effects Does nothing.
        /// \notes Can take any additional arguments.
        template <typename ... Args>
        static void handle(const source_location&, const char*, Args&&...) noexcept {}
    };

    /// The default handler that writes a message to `stderr`.
    /// Inherit from it in your module handler.
    struct default_handler
    {
        /// \effects Prints a message to `stderr`.
        /// \notes It can optionally accept an additional message string.
        /// \notes If `DEBUG_ASSERT_NO_STDIO` is defined, it will do nothing.
        static void handle(const source_location& loc, const char* expression, const char* message = nullptr) noexcept
        {
#ifndef DEBUG_ASSERT_NO_STDIO
            if (*expression == '\0')
            {
                if (message)
                    std::fprintf(stderr,
                                 "[debug assert] %s:%u: %s: Unreachable code reached - %s.\n",
                                loc.file_name, loc.line_number, loc.function_name, message);
                else
                    std::fprintf(stderr,
                                 "[debug assert] %s:%u: %s: Unreachable code reached.\n",
                                loc.file_name, loc.line_number, loc.function_name);
            }
            else if (message)
                std::fprintf(stderr,
                             "[debug assert] %s:%u: %s: Assertion '%s' failed - %s.\n",
                            loc.file_name, loc.line_number, loc.function_name,
                            expression, message);
            else
                std::fprintf(stderr,
                             "[debug assert] %s:%u: %s: Assertion '%s' failed.\n",
                            loc.file_name, loc.line_number, loc.function_name,
                            expression);
#else
            (void)loc;
            (void)expression;
            (void)message;
#endif
        }
    };

    /// \exclude
    namespace detail
    {
        //=== boilerplate ===//
        // from http://en.cppreference.com/w/cpp/types/remove_reference
        template <typename T>
        struct remove_reference
        {
            using type = T;
        };

        template <typename T>
        struct remove_reference<T&>
        {
            using type = T;
        };

        template <typename T>
        struct remove_reference<T&&>
        {
            using type = T;
        };

        // from http://stackoverflow.com/a/27501759
        template <class T>
        T&& forward(typename remove_reference<T>::type& t)
        {
            return static_cast<T&&>(t);
        }

        template <class T>
        T&& forward(typename remove_reference<T>::type&& t)
        {
            return static_cast<T&&>(t);
        }

        template <bool Value>
        struct enable_if;

        template <>
        struct enable_if<true>
        {
            using type = void;
        };

        template <>
        struct enable_if<false> {};

        //=== assert implementation ===//
        // use enable if instead of tag dispatching
        // this removes on additional function and encourage optimization
        template <class Expr, class Handler, unsigned Level, typename ... Args>
        auto do_assert(const Expr& expr, const source_location& loc, const char* expression,
                       Handler, level<Level>,
                       Args&&... args) noexcept
        -> typename enable_if<Level <= Handler::level>::type
        {
            static_assert(Level > 0, "level of an assertion must not be 0");
            if (!expr())
            {
                Handler::handle(loc, expression, forward<Args>(args)...);
                std::abort();
            }
        }

        template <class Expr, class Handler, unsigned Level, typename ... Args>
        DEBUG_ASSERT_FORCE_INLINE
        auto do_assert(const Expr& expr, const source_location&, const char*,
                       Handler, level<Level>,
                       Args&&...) noexcept
        -> typename enable_if<(Level > Handler::level)>::type
        {
            DEBUG_ASSERT_ASSUME(expr());
        }

        template <class Expr, class Handler, typename ... Args>
        auto do_assert(const Expr& expr, const source_location& loc, const char* expression,
                       Handler,
                       Args&&... args) noexcept
        -> typename enable_if<Handler::level != 0>::type
        {
            if (!expr())
            {
                Handler::handle(loc, expression, forward<Args>(args)...);
                std::abort();
            }
        }

        template <class Expr, class Handler, typename ... Args>
        DEBUG_ASSERT_FORCE_INLINE
        auto do_assert(const Expr& expr, const source_location&, const char*,
                       Handler,
                       Args&&...) noexcept
        -> typename enable_if<Handler::level == 0>::type
        {
            DEBUG_ASSERT_ASSUME(expr());
        }
    } // namespace detail
} // namespace debug_assert

//=== assertion macros ===//
#ifndef DEBUG_ASSERT_DISABLE
    /// The assertion macro.
    //
    /// Usage: `DEBUG_ASSERT(<expr>, <handler>, [<level>], [<handler-specific-args>].
    /// Where:
    /// * `<expr>` - the expression to check for, the expression `!<expr>` must be well-formed and contextually convertible to `bool`.
    /// * `<handler>` - an object of the module specific handler
    /// * `<level>` (optional, defaults to `1`) - the level of the assertion, must be an object of type [debug_assert::level<Level>]().
    /// * `<handler-specific-args>` (optional) - any additional arguments that are just forwarded to the handler function.
    ///
    /// It will only check the assertion if `<level>` is less than or equal to `Handler::level`.
    /// A failed assertion will call: `Handler::handle(location, expression, args)`.
    /// `location` is the [debug_assert::source_location]() at the macro expansion,
    /// `expression` is the stringified expression and `args` are the `<handler-specific-args>` as-is.
    /// If the handler function returns, it will call [std::abort()].
    ///
    /// \notes Define `DEBUG_ASSERT_DISABLE` to completely disable this macro, it will expand to nothing.
    /// This should not be necessary, the regular version is optimized away completely.
    #define DEBUG_ASSERT(Expr, ...) \
        debug_assert::detail::do_assert([&] { return Expr; }, DEBUG_ASSERT_CUR_SOURCE_LOCATION, #Expr, __VA_ARGS__)

    /// Marks a branch as unreachable.
    ///
    /// Usage: `DEBUG_UNREACHABLE(<handler>, [<level>], [<handler-specific-args>])`
    /// Where:
    /// * `<handler>` - an object of the module specific handler
    /// * `<level>` (optional, defaults to `1`) - the level of the assertion, must be an object of type [debug_assert::level<Level>]().
    /// * `<handler-specific-args>` (optional) - any additional arguments that are just forwarded to the handler function.
    ///
    /// It will only check the assertion if `<level>` is less than or equal to `Handler::level`.
    /// A failed assertion will call: `Handler::handle(location, "", args)`.
    /// and `args` are the `<handler-specific-args>` as-is.
    /// If the handler function returns, it will call [std::abort()].
    ///
    /// \notes Define `DEBUG_ASSERT_DISABLE` to completely disable this macro, it will expand to `DEBUG_ASSERT_MARK_UNREACHABLE`.
    /// This should not be necessary, the regular version is optimized away completely.
    #define DEBUG_UNREACHABLE(...) \
        debug_assert::detail::do_assert([&] { return false; }, DEBUG_ASSERT_CUR_SOURCE_LOCATION, "", __VA_ARGS__)
#else
    #define DEBUG_ASSERT(Expr, ...) DEBUG_ASSERT_ASSUME(Expr)

    #define DEBUG_UNREACHABLE(...) DEBUG_ASSERT_MARK_UNREACHABLE
#endif

#endif // DEBUG_ASSERT_HPP_INCLUDED


#define TYPE_SAFE_FORCE_INLINE DEBUG_ASSERT_FORCE_INLINE

#ifndef TYPE_SAFE_ENABLE_ASSERTIONS
#define TYPE_SAFE_ENABLE_ASSERTIONS 1
#endif

namespace type_safe
{
    namespace detail
    {
        struct assert_handler : debug_assert::set_level<TYPE_SAFE_ENABLE_ASSERTIONS>,
                                debug_assert::default_handler
        {
        };
    } // namespace detail
} // namespace type_safe
//=== end assertions boilerplate ===//

#ifndef TYPE_SAFE_INTEGER_HPP_INCLUDED
#define TYPE_SAFE_INTEGER_HPP_INCLUDED

#include <iosfwd>
#include <limits>
#include <type_traits>

namespace type_safe
{
    template <typename IntegerT>
    class integer;

    /// \exclude
    namespace detail
    {
        template <typename T>
        struct is_integer : std::integral_constant<bool, std::is_integral<T>::value
                                                             && !std::is_same<T, bool>::value
                                                             && !std::is_same<T, char>::value>
        {
        };

        template <typename From, typename To>
        struct is_safe_integer_conversion
            : std::integral_constant<bool, detail::is_integer<From>::value
                                               && detail::is_integer<To>::value
                                               && sizeof(From) <= sizeof(To)
                                               && std::is_signed<From>::value
                                                      == std::is_signed<To>::value>
        {
        };

        template <typename From, typename To>
        using enable_safe_integer_conversion =
            typename std::enable_if<is_safe_integer_conversion<From, To>::value>::type;

        template <typename From, typename To>
        using fallback_safe_integer_conversion =
            typename std::enable_if<!is_safe_integer_conversion<From, To>::value>::type;

        template <typename A, typename B>
        struct is_safe_integer_comparision
            : std::integral_constant<bool, is_safe_integer_conversion<A, B>::value
                                               || is_safe_integer_conversion<B, A>::value>
        {
        };

        template <typename A, typename B>
        using enable_safe_integer_comparision =
            typename std::enable_if<is_safe_integer_comparision<A, B>::value>::type;

        template <typename A, typename B>
        using fallback_safe_integer_comparision =
            typename std::enable_if<!is_safe_integer_comparision<A, B>::value>::type;

        template <typename A, typename B>
        struct is_safe_integer_operation
            : std::integral_constant<bool,
                                     detail::is_integer<A>::value && detail::is_integer<B>::value
                                         && std::is_signed<A>::value == std::is_signed<B>::value>
        {
        };

        template <typename A, typename B>
        struct integer_result_type
            : std::enable_if<is_safe_integer_operation<A, B>::value,
                             typename std::conditional<sizeof(A) < sizeof(B), B, A>::type>
        {
        };

        template <typename A, typename B>
        using integer_result_t = typename integer_result_type<A, B>::type;

        template <typename A, typename B>
        using fallback_integer_result =
            typename std::enable_if<!is_safe_integer_operation<A, B>::value>::type;

        template <typename T>
        constexpr bool will_underflow(T a, T b)
        {
            return !std::is_signed<T>::value && a < b;
        }

        template <typename T>
        constexpr bool will_overflow(T a, T b)
        {
            return !std::is_signed<T>::value && T(a + b) < a;
        }

        template <typename T>
        constexpr bool will_multiplication_overflow(T a, T b)
        {
            return !std::is_signed<T>::value && a != 0 && (T(a * b) / a) != b;
        }
    } // namespace detail

    /// A type safe integer class.
    ///
    /// This is a tiny, no overhead wrapper over a standard integer type.
    /// It behaves exactly like the built-in types except that narrowing conversions are not allowed.
    /// It also checks against `unsigned` under/overflow in debug mode
    /// and marks it as undefined for the optimizer otherwise.
    ///
    /// A conversion is considered safe if both integer types have the same signedness
    /// and the size of the value being converted is less than or equal to the destination size.
    ///
    /// \requires `IntegerT` must be an integral type except `bool` and `char` (use `signed char`/`unsigned char`).
    /// \notes It intentionally does not provide the bitwise operations.
    template <typename IntegerT>
    class integer
    {
        static_assert(detail::is_integer<IntegerT>::value, "must be a real integer type");

    public:
        using integer_type = IntegerT;

        //=== constructors ===//
        template <typename T, typename = detail::enable_safe_integer_conversion<T, integer_type>>
        TYPE_SAFE_FORCE_INLINE constexpr integer(const T& val) noexcept : value_(val)
        {
        }

        template <typename T, typename = detail::enable_safe_integer_conversion<T, integer_type>>
        TYPE_SAFE_FORCE_INLINE constexpr integer(const integer<T>& val) noexcept
            : value_(static_cast<T>(val))
        {
        }

        template <typename T, typename = detail::fallback_safe_integer_conversion<T, integer_type>>
        constexpr integer(T) = delete;

        //=== assignment ===//
        template <typename T, typename = detail::enable_safe_integer_conversion<T, integer_type>>
        TYPE_SAFE_FORCE_INLINE integer& operator=(const T& val) noexcept
        {
            value_ = val;
            return *this;
        }

        template <typename T, typename = detail::enable_safe_integer_conversion<T, integer_type>>
        TYPE_SAFE_FORCE_INLINE integer& operator=(const integer<T>& val) noexcept
        {
            value_ = static_cast<T>(val);
            return *this;
        }

        template <typename T, typename = detail::fallback_safe_integer_conversion<T, integer_type>>
        integer& operator=(T) = delete;

        //=== conversion back ===//
        TYPE_SAFE_FORCE_INLINE explicit constexpr operator integer_type() const noexcept
        {
            return value_;
        }

        //=== unary operators ===//
        TYPE_SAFE_FORCE_INLINE constexpr integer operator+() const noexcept
        {
            return *this;
        }

        TYPE_SAFE_FORCE_INLINE constexpr integer operator-() const noexcept
        {
            static_assert(std::is_signed<integer_type>::value,
                          "cannot call unary minus on unsigned integer");
            return -value_;
        }

        TYPE_SAFE_FORCE_INLINE integer& operator++() noexcept
        {
            DEBUG_ASSERT(!detail::will_overflow(value_, integer_type(1)), detail::assert_handler{},
                         "overflow detected");
            ++value_;
            return *this;
        }

        TYPE_SAFE_FORCE_INLINE integer operator++(int)noexcept
        {
            DEBUG_ASSERT(!detail::will_overflow(value_, integer_type(1)), detail::assert_handler{},
                         "overflow detected");
            auto res = *this;
            ++value_;
            return res;
        }

        TYPE_SAFE_FORCE_INLINE integer& operator--() noexcept
        {
            DEBUG_ASSERT(!detail::will_underflow(value_, integer_type(1)), detail::assert_handler{},
                         "underflow detected");
            --value_;
            return *this;
        }

        TYPE_SAFE_FORCE_INLINE integer operator--(int)noexcept
        {
            DEBUG_ASSERT(!detail::will_underflow(value_, integer_type(1)), detail::assert_handler{},
                         "underflow detected");
            auto res = *this;
            --value_;
            return res;
        }

//=== compound assignment ====//
#define TYPE_SAFE_DETAIL_MAKE_OP(Op)                                                               \
    template <typename T, typename = detail::enable_safe_integer_conversion<T, integer_type>>      \
    TYPE_SAFE_FORCE_INLINE integer& operator Op(const T& other) noexcept                           \
    {                                                                                              \
        return *this Op integer<T>(other);                                                         \
    }                                                                                              \
    template <typename T, typename = detail::fallback_safe_integer_conversion<T, integer_type>>    \
    integer& operator Op(integer<T>) = delete;                                                     \
    template <typename T, typename = detail::fallback_safe_integer_conversion<T, integer_type>>    \
    integer& operator Op(T) = delete;

        template <typename T, typename = detail::enable_safe_integer_conversion<T, integer_type>>
        TYPE_SAFE_FORCE_INLINE integer& operator+=(const integer<T>& other) noexcept
        {
            DEBUG_ASSERT(!detail::will_overflow(value_, static_cast<T>(other)),
                         detail::assert_handler{}, "overflow detected");
            value_ += static_cast<T>(other);
            return *this;
        }
        TYPE_SAFE_DETAIL_MAKE_OP(+=)

        template <typename T, typename = detail::enable_safe_integer_conversion<T, integer_type>>
        TYPE_SAFE_FORCE_INLINE integer& operator-=(const integer<T>& other) noexcept
        {
            DEBUG_ASSERT(!detail::will_underflow(value_, static_cast<T>(other)),
                         detail::assert_handler{}, "underflow detected");
            value_ -= static_cast<T>(other);
            return *this;
        }
        TYPE_SAFE_DETAIL_MAKE_OP(-=)

        template <typename T, typename = detail::enable_safe_integer_conversion<T, integer_type>>
        TYPE_SAFE_FORCE_INLINE integer& operator*=(const integer<T>& other) noexcept
        {
            DEBUG_ASSERT(!detail::will_multiplication_overflow(value_, static_cast<T>(other)),
                         detail::assert_handler{}, "overflow detected");
            value_ *= static_cast<T>(other);
            return *this;
        }
        TYPE_SAFE_DETAIL_MAKE_OP(*=)

        template <typename T, typename = detail::enable_safe_integer_conversion<T, integer_type>>
        TYPE_SAFE_FORCE_INLINE integer& operator/=(const integer<T>& other) noexcept
        {
            value_ /= static_cast<T>(other);
            return *this;
        }
        TYPE_SAFE_DETAIL_MAKE_OP(/=)

        template <typename T, typename = detail::enable_safe_integer_conversion<T, integer_type>>
        TYPE_SAFE_FORCE_INLINE integer& operator%=(const integer<T>& other) noexcept
        {
            value_ %= static_cast<T>(other);
            return *this;
        }
        TYPE_SAFE_DETAIL_MAKE_OP(%=)

#undef TYPE_SAFE_DETAIL_MAKE_OP

    private:
        integer_type value_;
    };

    //=== operations ===//
    /// \exclude
    namespace detail
    {
        template <typename T>
        struct make_signed;

        template <typename T>
        struct make_signed<integer<T>>
        {
            using type = integer<typename std::make_signed<T>::type>;
        };

        template <typename T>
        struct make_unsigned;

        template <typename T>
        struct make_unsigned<integer<T>>
        {
            using type = integer<typename std::make_unsigned<T>::type>;
        };
    } // namespace detail

    /// [std::make_signed]() for [type_safe::integer]().
    template <class Integer>
    using make_signed_t = typename detail::make_signed<Integer>::type;

    /// \returns A new [type_safe::integer]() of the corresponding signed integer type.
    /// \requires The value of `i` must fit into signed type.
    template <typename Integer>
    TYPE_SAFE_FORCE_INLINE constexpr make_signed_t<integer<Integer>> make_signed(
        const integer<Integer>& i) noexcept
    {
        using result_type = typename std::make_signed<Integer>::type;
        return i <= static_cast<Integer>(std::numeric_limits<result_type>::max()) ?
                   integer<result_type>(static_cast<result_type>(static_cast<Integer>(i))) :
                   (DEBUG_UNREACHABLE(detail::assert_handler{}, "conversion "
                                                                "would "
                                                                "overflow"),
                    result_type());
    }

    /// [std::make_unsigned]() for [type_safe::integer]().
    template <class Integer>
    using make_unsigned_t = typename detail::make_unsigned<Integer>::type;

    /// \returns A new [type_safe::integer]() of the corresponding unsigned integer type.
    /// \requires The value of `i` must not be negative.
    template <typename Integer>
    TYPE_SAFE_FORCE_INLINE constexpr make_unsigned_t<integer<Integer>> make_unsigned(
        const integer<Integer>& i) noexcept
    {
        using result_type = typename std::make_unsigned<Integer>::type;
        return i >= Integer(0) ?
                   integer<result_type>(static_cast<result_type>(static_cast<Integer>(i))) :
                   (DEBUG_UNREACHABLE(detail::assert_handler{}, "conversion would underflow"),
                    result_type(0));
    }

    /// \returns The absolute value of an [type_safe::integer]().
    /// \unique_name type_safe::abs-signed
    template <typename SignedInteger,
              typename = typename std::enable_if<std::is_signed<SignedInteger>::value>::type>
    TYPE_SAFE_FORCE_INLINE constexpr make_unsigned_t<integer<SignedInteger>> abs(
        const integer<SignedInteger>& i) noexcept
    {
        return make_unsigned(i > 0 ? i : -i);
    }

    /// \returns `i` unchanged.
    /// \notes This is an optimization of [type_safe::abs-signed]() for `unsigned` [type_safe::integer]().
    /// \unique_name type_safe::abs-unsigned
    template <typename UnsignedInteger,
              typename = typename std::enable_if<std::is_unsigned<UnsignedInteger>::value>::type>
    TYPE_SAFE_FORCE_INLINE constexpr integer<UnsignedInteger> abs(
        const integer<UnsignedInteger>& i) noexcept
    {
        return i;
    }

//=== comparision ===//
#define TYPE_SAFE_DETAIL_MAKE_OP(Op)                                                               \
    template <typename A, typename B, typename = detail::enable_safe_integer_conversion<A, B>>     \
    TYPE_SAFE_FORCE_INLINE constexpr bool operator Op(const A& a, const integer<B>& b)             \
    {                                                                                              \
        return integer<A>(a) Op b;                                                                 \
    }                                                                                              \
    template <typename A, typename B, typename = detail::enable_safe_integer_conversion<A, B>>     \
    TYPE_SAFE_FORCE_INLINE constexpr bool operator Op(const integer<A>& a, const B& b)             \
    {                                                                                              \
        return a Op integer<B>(b);                                                                 \
    }                                                                                              \
    template <typename A, typename B, typename = detail::fallback_safe_integer_comparision<A, B>>  \
    constexpr bool operator Op(integer<A>, integer<B>) = delete;                                   \
    template <typename A, typename B, typename = detail::fallback_safe_integer_comparision<A, B>>  \
    constexpr bool operator Op(A, integer<B>) = delete;                                            \
    template <typename A, typename B, typename = detail::fallback_safe_integer_comparision<A, B>>  \
    constexpr bool operator Op(integer<A>, B) = delete;

    template <typename A, typename B, typename = detail::enable_safe_integer_comparision<A, B>>
    TYPE_SAFE_FORCE_INLINE constexpr bool operator==(const integer<A>& a,
                                                     const integer<B>& b) noexcept
    {
        return static_cast<A>(a) == static_cast<B>(b);
    }
    TYPE_SAFE_DETAIL_MAKE_OP(==)

    template <typename A, typename B, typename = detail::enable_safe_integer_comparision<A, B>>
    TYPE_SAFE_FORCE_INLINE constexpr bool operator!=(const integer<A>& a,
                                                     const integer<B>& b) noexcept
    {
        return static_cast<A>(a) != static_cast<B>(b);
    }
    TYPE_SAFE_DETAIL_MAKE_OP(!=)

    template <typename A, typename B, typename = detail::enable_safe_integer_comparision<A, B>>
    TYPE_SAFE_FORCE_INLINE constexpr bool operator<(const integer<A>& a,
                                                    const integer<B>& b) noexcept
    {
        return static_cast<A>(a) < static_cast<B>(b);
    }
    TYPE_SAFE_DETAIL_MAKE_OP(<)

    template <typename A, typename B, typename = detail::enable_safe_integer_comparision<A, B>>
    TYPE_SAFE_FORCE_INLINE constexpr bool operator<=(const integer<A>& a,
                                                     const integer<B>& b) noexcept
    {
        return static_cast<A>(a) <= static_cast<B>(b);
    }
    TYPE_SAFE_DETAIL_MAKE_OP(<=)

    template <typename A, typename B, typename = detail::enable_safe_integer_comparision<A, B>>
    TYPE_SAFE_FORCE_INLINE constexpr bool operator>(const integer<A>& a,
                                                    const integer<B>& b) noexcept
    {
        return static_cast<A>(a) > static_cast<B>(b);
    }
    TYPE_SAFE_DETAIL_MAKE_OP(>)

    template <typename A, typename B, typename = detail::enable_safe_integer_comparision<A, B>>
    TYPE_SAFE_FORCE_INLINE constexpr bool operator>=(const integer<A>& a,
                                                     const integer<B>& b) noexcept
    {
        return static_cast<A>(a) >= static_cast<B>(b);
    }
    TYPE_SAFE_DETAIL_MAKE_OP(>=)

#undef TYPE_SAFE_DETAIL_MAKE_OP

//=== binary operations ===//
#define TYPE_SAFE_DETAIL_MAKE_OP(Op)                                                               \
    template <typename A, typename B>                                                              \
    TYPE_SAFE_FORCE_INLINE constexpr auto operator Op(const A& a, const integer<B>& b) noexcept    \
        ->integer<detail::integer_result_t<A, B>>                                                  \
    {                                                                                              \
        return integer<A>(a) Op b;                                                                 \
    }                                                                                              \
    template <typename A, typename B>                                                              \
    TYPE_SAFE_FORCE_INLINE constexpr auto operator Op(const integer<A>& a, const B& b) noexcept    \
        ->integer<detail::integer_result_t<A, B>>                                                  \
    {                                                                                              \
        return a Op integer<B>(b);                                                                 \
    }                                                                                              \
    template <typename A, typename B, typename = detail::fallback_integer_result<A, B>>            \
    constexpr int operator Op(integer<A>, integer<B>) noexcept = delete;                           \
    template <typename A, typename B, typename = detail::fallback_integer_result<A, B>>            \
    constexpr int operator Op(A, integer<B>) noexcept = delete;                                    \
    template <typename A, typename B, typename = detail::fallback_integer_result<A, B>>            \
    constexpr int operator Op(integer<A>, B) noexcept = delete;

    template <typename A, typename B>
    TYPE_SAFE_FORCE_INLINE constexpr auto operator+(const integer<A>& a,
                                                    const integer<B>& b) noexcept
        -> integer<detail::integer_result_t<A, B>>
    {
        return detail::will_overflow<detail::integer_result_t<A, B>>(static_cast<A>(a),
                                                                     static_cast<B>(b)) ?
                   (DEBUG_UNREACHABLE(detail::assert_handler{}, "overflow detected"), A()) :
                   detail::integer_result_t<A, B>(static_cast<A>(a) + static_cast<B>(b));
    }
    TYPE_SAFE_DETAIL_MAKE_OP(+)

    template <typename A, typename B>
    TYPE_SAFE_FORCE_INLINE constexpr auto operator-(const integer<A>& a,
                                                    const integer<B>& b) noexcept
        -> integer<detail::integer_result_t<A, B>>
    {
        return detail::will_underflow<detail::integer_result_t<A, B>>(static_cast<A>(a),
                                                                      static_cast<B>(b)) ?
                   (DEBUG_UNREACHABLE(detail::assert_handler{}, "underflow detected"), A()) :
                   detail::integer_result_t<A, B>(static_cast<A>(a) - static_cast<B>(b));
    }
    TYPE_SAFE_DETAIL_MAKE_OP(-)

    template <typename A, typename B>
    TYPE_SAFE_FORCE_INLINE constexpr auto operator*(const integer<A>& a,
                                                    const integer<B>& b) noexcept
        -> integer<detail::integer_result_t<A, B>>
    {
        return detail::will_multiplication_overflow<detail::integer_result_t<A, B>>(static_cast<A>(
                                                                                        a),
                                                                                    static_cast<B>(
                                                                                        b)) ?
                   (DEBUG_UNREACHABLE(detail::assert_handler{}, "overflow detected"), A()) :
                   detail::integer_result_t<A, B>(static_cast<A>(a) * static_cast<B>(b));
    }
    TYPE_SAFE_DETAIL_MAKE_OP(*)

    template <typename A, typename B>
    TYPE_SAFE_FORCE_INLINE constexpr auto operator/(const integer<A>& a,
                                                    const integer<B>& b) noexcept
        -> integer<detail::integer_result_t<A, B>>
    {
        return detail::integer_result_t<A, B>(static_cast<A>(a) / static_cast<B>(b));
    }
    TYPE_SAFE_DETAIL_MAKE_OP(/)

    template <typename A, typename B>
    TYPE_SAFE_FORCE_INLINE constexpr auto operator%(const integer<A>& a,
                                                    const integer<B>& b) noexcept
        -> integer<detail::integer_result_t<A, B>>
    {
        return detail::integer_result_t<A, B>(static_cast<A>(a) % static_cast<B>(b));
    }
    TYPE_SAFE_DETAIL_MAKE_OP(%)

#undef TYPE_SAFE_DETAIL_MAKE_OP

    //=== input/output ===/
    template <typename Char, class CharTraits, typename IntegerT>
    std::basic_istream<Char, CharTraits>& operator>>(std::basic_istream<Char, CharTraits>& in,
                                                     integer<IntegerT>& i)
    {
        IntegerT val;
        in >> val;
        i = val;
        return in;
    }

    template <typename Char, class CharTraits, typename IntegerT>
    std::basic_ostream<Char, CharTraits>& operator<<(std::basic_ostream<Char, CharTraits>& out,
                                                     const integer<IntegerT>& i)
    {
        return out << static_cast<IntegerT>(i);
    }
} // namespace type_safe

#endif // TYPE_SAFE_INTEGER_HPP_INCLUDED