libostd/ostd/type_traits.hh

/* Type traits for OctaSTD.
 *
 * This file is part of OctaSTD. See COPYING.md for futher information.
 */

#ifndef OSTD_TYPE_TRAITS_HH
#define OSTD_TYPE_TRAITS_HH

#include <stddef.h>

#include "ostd/types.hh"

namespace ostd {
/* forward declarations */

namespace detail {
    template<typename> struct RemoveCvBase;
    template<typename> struct AddLr;
    template<typename> struct AddRr;
    template<typename> struct AddConstBase;
    template<typename> struct RemoveReferenceBase;
    template<typename> struct RemoveAllExtentsBase;

    template<typename ...> struct CommonTypeBase;
}

template<typename T>
using RemoveCv = typename detail::RemoveCvBase<T>::Type;

template<typename T>
using AddLvalueReference = typename detail::AddLr<T>::Type;

template<typename T>
using AddRvalueReference = typename detail::AddRr<T>::Type;

template<typename T>
using AddConst = typename detail::AddConstBase<T>::Type;

template<typename T>
using RemoveReference = typename detail::RemoveReferenceBase<T>::Type;

template<typename T>
using RemoveAllExtents = typename detail::RemoveAllExtentsBase<T>::Type;

namespace detail {
    template<typename T> AddRvalueReference<T> declval_in();
}

/* integral constant */

template<typename T, T val>
struct Constant {
    static constexpr T value = val;

    using Value = T;
    using Type = Constant<T, val>;

    constexpr operator Value() const { return value; }
    constexpr Value operator()() const { return value; }
};

template<bool val>
using BoolConstant = Constant<bool, val>;

using True = BoolConstant<true>;
using False = BoolConstant<false>;

template<typename T, T val> constexpr T Constant<T, val>::value;

/* type equality */

template<typename, typename> constexpr bool IsSame       = false;
template<typename T        > constexpr bool IsSame<T, T> = true;

/* is void */

template<typename T>
constexpr bool IsVoid = IsSame<RemoveCv<T>, void>;

/* is null pointer */

template<typename T>
constexpr bool IsNullPointer = IsSame<RemoveCv<T>, Nullptr>;

/* is integer */

namespace detail {
    template<typename> constexpr bool IsIntegralBase = false;

    template<> constexpr bool IsIntegralBase<bool  > = true;
    template<> constexpr bool IsIntegralBase<char  > = true;
    template<> constexpr bool IsIntegralBase<short > = true;
    template<> constexpr bool IsIntegralBase<int   > = true;
    template<> constexpr bool IsIntegralBase<long  > = true;

    template<> constexpr bool IsIntegralBase<sbyte > = true;
    template<> constexpr bool IsIntegralBase<byte  > = true;
    template<> constexpr bool IsIntegralBase<ushort> = true;
    template<> constexpr bool IsIntegralBase<uint  > = true;
    template<> constexpr bool IsIntegralBase<ulong > = true;
    template<> constexpr bool IsIntegralBase<llong > = true;
    template<> constexpr bool IsIntegralBase<ullong> = true;

    template<> constexpr bool IsIntegralBase<Char16> = true;
    template<> constexpr bool IsIntegralBase<Char32> = true;
    template<> constexpr bool IsIntegralBase<Wchar > = true;
}

template<typename T>
constexpr bool IsIntegral = detail::IsIntegralBase<RemoveCv<T>>;

/* is floating point */

namespace detail {
    template<typename> constexpr bool IsFloatingPointBase = false;

    template<> constexpr bool IsFloatingPointBase<float > = true;
    template<> constexpr bool IsFloatingPointBase<double> = true;

    template<> constexpr bool IsFloatingPointBase<ldouble> = true;
}

template<typename T>
constexpr bool IsFloatingPoint = detail::IsFloatingPointBase<RemoveCv<T>>;

/* is array */

template<typename          > constexpr bool IsArray       = false;
template<typename T        > constexpr bool IsArray<T[ ]> = true;
template<typename T, Size N> constexpr bool IsArray<T[N]> = true;

/* is pointer */

namespace detail {
    template<typename  > constexpr bool IsPointerBase      = false;
    template<typename T> constexpr bool IsPointerBase<T *> = true;
}

template<typename T>
constexpr bool IsPointer = detail::IsPointerBase<RemoveCv<T>>;

/* is lvalue reference */

template<typename  > constexpr bool IsLvalueReference      = false;
template<typename T> constexpr bool IsLvalueReference<T &> = true;

/* is rvalue reference */

template<typename  > constexpr bool IsRvalueReference       = false;
template<typename T> constexpr bool IsRvalueReference<T &&> = true;

/* is reference */

template<typename T>
constexpr bool IsReference = IsLvalueReference<T> || IsRvalueReference<T>;

/* is enum */

template<typename T> constexpr bool IsEnum = __is_enum(T);

/* is union */

template<typename T> constexpr bool IsUnion = __is_union(T);

/* is class */

template<typename T> constexpr bool IsClass = __is_class(T);

/* is function */

namespace detail {
    struct FunctionTestDummy {};

    template<typename T> char function_test(T *);
    template<typename T> char function_test(FunctionTestDummy);
    template<typename T> int  function_test(...);

    template<typename T> T                 &function_source(int);
    template<typename T> FunctionTestDummy  function_source(...);

    template<typename T, bool = IsClass<T> ||
                                IsUnion<T> ||
                                IsVoid<T> ||
                                IsReference<T> ||
                                IsNullPointer<T>>
    constexpr bool IsFunctionBase
        = sizeof(function_test<T>(function_source<T>(0))) == 1;

    template<typename T> constexpr bool IsFunctionBase<T, true> = false;
} /* namespace detail */

template<typename T>
constexpr bool IsFunction = detail::IsFunctionBase<T>;

/* is arithmetic */

template<typename T>
constexpr bool IsArithmetic = IsIntegral<T> || IsFloatingPoint<T>;

/* is fundamental */

template<typename T>
constexpr bool IsFundamental = IsArithmetic<T> || IsVoid<T> || IsNullPointer<T>;

/* is compound */

template<typename T>
constexpr bool IsCompound = !IsFundamental<T>;

/* is pointer to member */

namespace detail {
    template<typename> constexpr bool IsMemberPointerBase = false;

    template<typename T, typename U>
    constexpr bool IsMemberPointerBase<T U::*> = true;
}

template<typename T>
constexpr bool IsMemberPointer = detail::IsMemberPointerBase<RemoveCv<T>>;

/* is pointer to member object */

namespace detail {
    template<typename> constexpr bool IsMemberObjectPointerBase = false;

    template<typename T, typename U>
    constexpr bool IsMemberObjectPointerBase<T U::*> = !IsFunction<T>;
}

template<typename T>
constexpr bool IsMemberObjectPointer = detail::IsMemberObjectPointerBase<RemoveCv<T>>;

/* is pointer to member function */

namespace detail {
    template<typename> constexpr bool IsMemberFunctionPointerBase = false;

    template<typename T, typename U>
    constexpr bool IsMemberFunctionPointerBase<T U::*> = IsFunction<T>;
}

template<typename T>
constexpr bool IsMemberFunctionPointer = detail::IsMemberFunctionPointerBase<RemoveCv<T>>;

/* is object */

template<typename T>
constexpr bool IsObject = !IsFunction<T> && !IsVoid<T> && !IsReference<T>;

/* is scalar */

template<typename T> constexpr bool IsScalar
    = IsMemberPointer<T> || IsPointer<T> || IsEnum<T> ||
      IsNullPointer  <T> || IsArithmetic<T>;

/* is abstract */

template<typename T> constexpr bool IsAbstract = __is_abstract(T);

/* is const */

template<typename T>
constexpr bool IsConst = IsSame<T, const T>;

/* is volatile */

template<typename T>
constexpr bool IsVolatile = IsSame<T, volatile T>;

/* is empty */

template<typename T> constexpr bool IsEmpty = __is_empty(T);

/* is POD */

template<typename T> constexpr bool IsPod = __is_pod(T);

/* is polymorphic */

template<typename T> constexpr bool IsPolymorphic = __is_polymorphic(T);

/* is signed */

namespace detail {
    template<typename T> constexpr bool IsSignedCore = T(-1) < T(0);

    template<typename T, bool = IsArithmetic<T>>
    constexpr bool IsSignedBase = false;

    template<typename T>
    constexpr bool IsSignedBase<T, true> = detail::IsSignedCore<T>;
}

template<typename T>
constexpr bool IsSigned = detail::IsSignedBase<T>;

/* is unsigned */

namespace detail {
    template<typename T> constexpr bool IsUnsignedCore = T(0) < T(-1);

    template<typename T, bool = IsArithmetic<T>>
    constexpr bool IsUnsignedBase = false;

    template<typename T>
    constexpr bool IsUnsignedBase<T, true> = detail::IsUnsignedCore<T>;
}

template<typename T>
constexpr bool IsUnsigned = detail::IsUnsignedBase<T>;

/* is standard layout */

template<typename T>
constexpr bool IsStandardLayout = __is_standard_layout(T);

/* is literal type */

template<typename T>
constexpr bool IsLiteralType = __is_literal_type(T);

/* is trivially copyable */

template<typename T>
constexpr bool IsTriviallyCopyable = IsScalar<RemoveAllExtents<T>>;

/* is trivial */

template<typename T> constexpr bool IsTrivial = __is_trivial(T);

/* has virtual destructor */

template<typename T>
constexpr bool HasVirtualDestructor = __has_virtual_destructor(T);

/* is constructible */

namespace detail {
#define OSTD_MOVE(v) static_cast<RemoveReference<decltype(v)> &&>(v)

    template<typename, typename T> struct Select2nd { using Type = T; };
    struct Any { Any(...); };

    template<typename T, typename ...A> typename Select2nd<
        decltype(OSTD_MOVE(T(declval_in<A>()...))), True
    >::Type is_ctible_test(T &&, A &&...);

#undef OSTD_MOVE

    template<typename ...A> False is_ctible_test(Any, A &&...);

    template<bool, typename T, typename ...A>
    constexpr bool CtibleCore = CommonTypeBase<
        decltype(is_ctible_test(declval_in<T>(), declval_in<A>()...))
    >::Type::value;

    /* function types are not constructible */
    template<typename R, typename ...A1, typename ...A2>
    constexpr bool CtibleCore<false, R(A1...), A2...> = false;

    /* scalars are default constructible, refs are not */
    template<typename T>
    constexpr bool CtibleCore<true, T> = IsScalar<T>;

    /* scalars and references are constructible from one arg if
     * implicitly convertible to scalar or reference */
    template<typename T>
    struct CtibleRef {
        static True  test(T);
        static False test(...);
    };

    template<typename T, typename U>
    constexpr bool CtibleCore<true, T, U> = CommonTypeBase<
        decltype(CtibleRef<T>::test(declval_in<U>()))
    >::Type::value;

    /* scalars and references are not constructible from multiple args */
    template<typename T, typename U, typename ...A>
    constexpr bool CtibleCore<true, T, U, A...> = false;

    /* treat scalars and refs separately */
    template<bool, typename T, typename ...A>
    constexpr bool CtibleVoidCheck = CtibleCore<
        (IsScalar<T> || IsReference<T>), T, A...
    >;

    /* if any of T or A is void, IsConstructible should be false */
    template<typename T, typename ...A>
    constexpr bool CtibleVoidCheck<true, T, A...> = false;

    template<typename ...A> constexpr bool CtibleContainsVoid = false;

    template<> constexpr bool CtibleContainsVoid<> = false;

    template<typename T, typename ...A>
    constexpr bool CtibleContainsVoid<T, A...>
        = IsVoid<T> || CtibleContainsVoid<A...>;

    /* entry point */
    template<typename T, typename ...A>
    constexpr bool Ctible = CtibleVoidCheck<
        CtibleContainsVoid<T, A...> || IsAbstract<T>, T, A...
    >;

    /* array types are default constructible if their element type is */
    template<typename T, Size N>
    constexpr bool CtibleCore<false, T[N]> = Ctible<RemoveAllExtents<T>>;

    /* otherwise array types are not constructible by this syntax */
    template<typename T, Size N, typename ...A>
    constexpr bool CtibleCore<false, T[N], A...> = false;

    /* incomplete array types are not constructible */
    template<typename T, typename ...A>
    constexpr bool CtibleCore<false, T[], A...> = false;
} /* namespace detail */

template<typename T, typename ...A>
constexpr bool IsConstructible = detail::Ctible<T, A...>;

/* is default constructible */

template<typename T>
constexpr bool IsDefaultConstructible = IsConstructible<T>;

/* is copy constructible */

template<typename T>
constexpr bool IsCopyConstructible = IsConstructible<T,
    AddLvalueReference<AddConst<T>>
>;

/* is move constructible */

template<typename T>
constexpr bool IsMoveConstructible = IsConstructible<T,
    AddRvalueReference<T>
>;

/* is assignable */

namespace detail {
    template<typename T, typename U> typename detail::Select2nd<
        decltype((declval_in<T>() = declval_in<U>())), True
    >::Type assign_test(T &&, U &&);

    template<typename T> False assign_test(Any, T &&);

    template<typename T, typename U, bool = IsVoid<T> || IsVoid<U>>
    constexpr bool IsAssignableBase = CommonTypeBase<
        decltype(assign_test(declval_in<T>(), declval_in<U>()))
    >::Type::value;

    template<typename T, typename U>
    constexpr bool IsAssignableBase<T, U, true> = false;
} /* namespace detail */

template<typename T, typename U>
constexpr bool IsAssignable = detail::IsAssignableBase<T, U>;

/* is copy assignable */

template<typename T>
constexpr bool IsCopyAssignable = IsAssignable<
    AddLvalueReference<T>,
    AddLvalueReference<AddConst<T>>
>;

/* is move assignable */

template<typename T>
constexpr bool IsMoveAssignable = IsAssignable<
    AddLvalueReference<T>,
    const AddRvalueReference<T>
>;

/* is destructible */

namespace detail {
    template<typename> struct IsDtibleApply { using Type = int; };

    template<typename T> struct IsDestructorWellformed {
        template<typename TT> static char test(typename IsDtibleApply<
            decltype(detail::declval_in<TT &>().~TT())
        >::Type);

        template<typename TT> static int test(...);

        static constexpr bool value = (sizeof(test<T>(12)) == sizeof(char));
    };

    template<typename, bool> constexpr bool DtibleImpl = false;

    template<typename T>
    constexpr bool DtibleImpl<T, false>
        = IsDestructorWellformed<RemoveAllExtents<T>>::value;

    template<typename T>
    constexpr bool DtibleImpl<T, true> = true;

    template<typename T, bool> constexpr bool DtibleFalse = false;

    template<typename T> constexpr bool DtibleFalse<T, false>
        = DtibleImpl<T, IsReference<T>>;

    template<typename T> constexpr bool DtibleFalse<T, true> = false;

    template<typename T>
    constexpr bool IsDestructibleBase = detail::DtibleFalse<T, IsFunction<T>>;

    template<typename T> constexpr bool IsDestructibleBase<T[] > = false;
    template<          > constexpr bool IsDestructibleBase<void> = false;
} /* namespace detail */

template<typename T>
constexpr bool IsDestructible = detail::IsDestructibleBase<T>;

/* is trivially constructible */

namespace detail {
    template<typename T, typename ...A>
    constexpr bool IsTriviallyConstructibleBase = false;

    template<typename T>
    constexpr bool IsTriviallyConstructibleBase<T>
        = __has_trivial_constructor(T);

    template<typename T>
    constexpr bool IsTriviallyConstructibleBase<T, T &>
        = __has_trivial_copy(T);

    template<typename T>
    constexpr bool IsTriviallyConstructibleBase<T, const T &>
        = __has_trivial_copy(T);

    template<typename T>
    constexpr bool IsTriviallyConstructibleBase<T, T &&>
        = __has_trivial_copy(T);
} /* namespace detail */

template<typename T, typename ...A>
constexpr bool IsTriviallyConstructible
    = detail::IsTriviallyConstructibleBase<T, A...>;

/* is trivially default constructible */

template<typename T> constexpr bool IsTriviallyDefaultConstructible
    = IsTriviallyConstructible<T>;

/* is trivially copy constructible */

template<typename T> constexpr bool IsTriviallyCopyConstructible
    = IsTriviallyConstructible<T, AddLvalueReference<const T>>;

/* is trivially move constructible */

template<typename T> constexpr bool IsTriviallyMoveConstructible
    = IsTriviallyConstructible<T, AddRvalueReference<T>>;

/* is trivially assignable */

namespace detail {
    template<typename T, typename ...A>
    constexpr bool IsTriviallyAssignableBase = false;

    template<typename T>
    constexpr bool IsTriviallyAssignableBase<T>
        = __has_trivial_assign(T);

    template<typename T>
    constexpr bool IsTriviallyAssignableBase<T, T &>
        = __has_trivial_copy(T);

    template<typename T>
    constexpr bool IsTriviallyAssignableBase<T, const T &>
        = __has_trivial_copy(T);

    template<typename T>
    constexpr bool IsTriviallyAssignableBase<T, T &&>
        = __has_trivial_copy(T);
} /* namespace detail */

template<typename T, typename ...A>
constexpr bool IsTriviallyAssignable
    = detail::IsTriviallyAssignableBase<T>;

/* is trivially copy assignable */

template<typename T> constexpr bool IsTriviallyCopyAssignable
    = IsTriviallyAssignable<T, AddLvalueReference<const T>>;

/* is trivially move assignable */

template<typename T> constexpr bool IsTriviallyMoveAssignable
    = IsTriviallyAssignable<T, AddRvalueReference<T>>;

/* is trivially destructible */

template<typename T>
constexpr bool IsTriviallyDestructible = __has_trivial_destructor(T);

/* is base of */

template<typename B, typename D>
constexpr bool IsBaseOf = __is_base_of(B, D);

/* is convertible */

namespace detail {
    template<typename F, typename T, bool = IsVoid<F>
        || IsFunction<T> || IsArray<T>
    > struct IsConvertibleBase {
        static constexpr bool value = IsVoid<T>;
    };

    template<typename F, typename T>
    struct IsConvertibleBase<F, T, false> {
        template<typename TT> static void test_f(TT);

        template<typename FF, typename TT,
            typename = decltype(test_f<TT>(declval_in<FF>()))
        > static True test(int);

        template<typename, typename> static False test(...);

        static constexpr bool value = decltype(test<F, T>(0))::value;
    };
}

template<typename F, typename T> constexpr bool IsConvertible
    = detail::IsConvertibleBase<F, T>::value;

/* extent */

namespace detail {
    template<typename, uint> constexpr Size ExtentBase = 0;

    template<typename T>
    constexpr Size ExtentBase<T[], 0> = 0;

    template<typename T, uint I>
    constexpr Size ExtentBase<T[], I> = detail::ExtentBase<T, I - 1>;

    template<typename T, Size N>
    constexpr Size ExtentBase<T[N], 0> = N;

    template<typename T, Size N, uint I>
    constexpr Size ExtentBase<T[N], I> = detail::ExtentBase<T, I - 1>;
} /* namespace detail */

template<typename T, uint I = 0>
constexpr Size Extent = detail::ExtentBase<T, I>;

/* rank */

namespace detail {
    template<typename> constexpr Size RankBase = 0;

    template<typename T>
    constexpr Size RankBase<T[]> = detail::RankBase<T> + 1;

    template<typename T, Size N>
    constexpr Size RankBase<T[N]> = detail::RankBase<T> + 1;
}

template<typename T> constexpr Size Rank = detail::RankBase<T>;

/* remove const, volatile, cv */

namespace detail {
    template<typename T>
    struct RemoveConstBase          { using Type = T; };
    template<typename T>
    struct RemoveConstBase<const T> { using Type = T; };

    template<typename T>
    struct RemoveVolatileBase             { using Type = T; };
    template<typename T>
    struct RemoveVolatileBase<volatile T> { using Type = T; };
}

template<typename T>
using RemoveConst = typename detail::RemoveConstBase<T>::Type;
template<typename T>
using RemoveVolatile = typename detail::RemoveVolatileBase<T>::Type;

namespace detail {
    template<typename T>
    struct RemoveCvBase {
        using Type = RemoveVolatile<RemoveConst<T>>;
    };
}

/* add const, volatile, cv */

namespace detail {
    template<typename T, bool = IsReference<T> || IsFunction<T> || IsConst<T>>
    struct AddConstCore { using Type = T; };

    template<typename T> struct AddConstCore<T, false> {
        using Type = const T;
    };

    template<typename T> struct AddConstBase {
        using Type = typename AddConstCore<T>::Type;
    };

    template<typename T, bool = IsReference<T> || IsFunction<T> || IsVolatile<T>>
    struct AddVolatileCore { using Type = T; };

    template<typename T> struct AddVolatileCore<T, false> {
        using Type = volatile T;
    };

    template<typename T> struct AddVolatileBase {
        using Type = typename AddVolatileCore<T>::Type;
    };
}

template<typename T>
using AddVolatile = typename detail::AddVolatileBase<T>::Type;

namespace detail {
    template<typename T>
    struct AddCvBase {
        using Type = AddConst<AddVolatile<T>>;
    };
}

template<typename T>
using AddCv = typename detail::AddCvBase<T>::Type;

/* remove reference */

namespace detail {
    template<typename T>
    struct RemoveReferenceBase       { using Type = T; };
    template<typename T>
    struct RemoveReferenceBase<T &>  { using Type = T; };
    template<typename T>
    struct RemoveReferenceBase<T &&> { using Type = T; };
}

/* remove pointer */

namespace detail {
    template<typename T>
    struct RemovePointerBase                     { using Type = T; };
    template<typename T>
    struct RemovePointerBase<T *               > { using Type = T; };
    template<typename T>
    struct RemovePointerBase<T * const         > { using Type = T; };
    template<typename T>
    struct RemovePointerBase<T * volatile      > { using Type = T; };
    template<typename T>
    struct RemovePointerBase<T * const volatile> { using Type = T; };
}

template<typename T>
using RemovePointer = typename detail::RemovePointerBase<T>::Type;

/* add pointer */

namespace detail {
    template<typename T> struct AddPointerBase {
        using Type = RemoveReference<T> *;
    };
}

template<typename T>
using AddPointer = typename detail::AddPointerBase<T>::Type;

/* add lvalue reference */

namespace detail {
    template<typename T> struct AddLr      { using Type = T &; };
    template<typename T> struct AddLr<T &> { using Type = T &; };
    template<> struct AddLr<void> {
        using Type = void;
    };
    template<> struct AddLr<const void> {
        using Type = const void;
    };
    template<> struct AddLr<volatile void> {
        using Type = volatile void;
    };
    template<> struct AddLr<const volatile void> {
        using Type = const volatile void;
    };
}

/* add rvalue reference */

namespace detail {
    template<typename T> struct AddRr { using Type = T &&; };
    template<> struct AddRr<void> {
        using Type = void;
    };
    template<> struct AddRr<const void> {
        using Type = const void;
    };
    template<> struct AddRr<volatile void> {
        using Type = volatile void;
    };
    template<> struct AddRr<const volatile void> {
        using Type = const volatile void;
    };
}

/* remove extent */

namespace detail {
    template<typename T>
    struct RemoveExtentBase       { using Type = T; };
    template<typename T>
    struct RemoveExtentBase<T[ ]> { using Type = T; };
    template<typename T, Size N>
    struct RemoveExtentBase<T[N]> { using Type = T; };
}

template<typename T>
using RemoveExtent = typename detail::RemoveExtentBase<T>::Type;

/* remove all extents */

namespace detail {
    template<typename T> struct RemoveAllExtentsBase { using Type = T; };

    template<typename T> struct RemoveAllExtentsBase<T[]> {
        using Type = RemoveAllExtentsBase<T>;
    };

    template<typename T, Size N> struct RemoveAllExtentsBase<T[N]> {
        using Type = RemoveAllExtentsBase<T>;
    };
}

/* make (un)signed
 *
 * this is bad, but i don't see any better way
 * shamelessly copied from graphitemaster @ neothyne
 */

namespace detail {
    template<typename T, typename U> struct TypeList {
        using First = T;
        using Rest = U;
    };

    /* not a type */
    struct TlNat {
        TlNat() = delete;
        TlNat(const TlNat &) = delete;
        TlNat &operator=(const TlNat &) = delete;
        ~TlNat() = delete;
    };

    using Stypes = TypeList<sbyte,
                   TypeList<short,
                   TypeList<int,
                   TypeList<long,
                   TypeList<llong, TlNat>>>>>;

    using Utypes = TypeList<byte,
                   TypeList<ushort,
                   TypeList<uint,
                   TypeList<ulong,
                   TypeList<ullong, TlNat>>>>>;

    template<typename T, Size N, bool = (N <= sizeof(typename T::First))>
    struct TypeFindFirst;

    template<typename T, typename U, Size N>
    struct TypeFindFirst<TypeList<T, U>, N, true> {
        using Type = T;
    };

    template<typename T, typename U, Size N>
    struct TypeFindFirst<TypeList<T, U>, N, false> {
        using Type = typename TypeFindFirst<U, N>::Type;
    };

    template<typename T, typename U,
        bool = IsConst<RemoveReference<T>>,
        bool = IsVolatile<RemoveReference<T>>
    > struct ApplyCv {
        using Type = U;
    };

    template<typename T, typename U>
    struct ApplyCv<T, U, true, false> { /* const */
        using Type = const U;
    };

    template<typename T, typename U>
    struct ApplyCv<T, U, false, true> { /* volatile */
        using Type = volatile U;
    };

    template<typename T, typename U>
    struct ApplyCv<T, U, true, true> { /* const volatile */
        using Type = const volatile U;
    };

    template<typename T, typename U>
    struct ApplyCv<T &, U, true, false> { /* const */
        using Type = const U &;
    };

    template<typename T, typename U>
    struct ApplyCv<T &, U, false, true> { /* volatile */
        using Type = volatile U &;
    };

    template<typename T, typename U>
    struct ApplyCv<T &, U, true, true> { /* const volatile */
        using Type = const volatile U &;
    };

    template<typename T, bool = IsIntegral<T> || IsEnum<T>>
    struct MakeSignedCore {};

    template<typename T, bool = IsIntegral<T> || IsEnum<T>>
    struct MakeUnsignedCore {};

    template<typename T>
    struct MakeSignedCore<T, true> {
        using Type = typename TypeFindFirst<Stypes, sizeof(T)>::Type;
    };

    template<typename T>
    struct MakeUnsignedCore<T, true> {
        using Type = typename TypeFindFirst<Utypes, sizeof(T)>::Type;
    };

    template<> struct MakeSignedCore<bool  , true> {};
    template<> struct MakeSignedCore<short , true> { using Type = short; };
    template<> struct MakeSignedCore<int   , true> { using Type = int; };
    template<> struct MakeSignedCore<long  , true> { using Type = long; };

    template<> struct MakeSignedCore<sbyte , true> { using Type = sbyte; };
    template<> struct MakeSignedCore<byte  , true> { using Type = sbyte; };
    template<> struct MakeSignedCore<ushort, true> { using Type = short; };
    template<> struct MakeSignedCore<uint  , true> { using Type = int;   };
    template<> struct MakeSignedCore<ulong , true> { using Type = long;  };
    template<> struct MakeSignedCore<llong , true> { using Type = llong; };
    template<> struct MakeSignedCore<ullong, true> { using Type = llong; };

    template<> struct MakeUnsignedCore<bool  , true> {};
    template<> struct MakeUnsignedCore<short , true> { using Type = ushort; };
    template<> struct MakeUnsignedCore<int   , true> { using Type = uint;   };
    template<> struct MakeUnsignedCore<long  , true> { using Type = ulong;  };

    template<> struct MakeUnsignedCore<sbyte , true> { using Type = byte;   };
    template<> struct MakeUnsignedCore<byte  , true> { using Type = byte;   };
    template<> struct MakeUnsignedCore<ushort, true> { using Type = ushort; };
    template<> struct MakeUnsignedCore<uint  , true> { using Type = uint;   };
    template<> struct MakeUnsignedCore<ulong , true> { using Type = ulong;  };
    template<> struct MakeUnsignedCore<llong , true> { using Type = ullong; };
    template<> struct MakeUnsignedCore<ullong, true> { using Type = ullong; };

    template<typename T> struct MakeSignedBase {
        using Type = typename ApplyCv<T,
            typename MakeSignedCore<RemoveCv<T>>::Type
        >::Type;
    };

    template<typename T> struct MakeUnsignedBase {
        using Type = typename ApplyCv<T,
            typename MakeUnsignedCore<RemoveCv<T>>::Type
        >::Type;
    };
} /* namespace detail */

template<typename T>
using MakeSigned = typename detail::MakeSignedBase<T>::Type;
template<typename T>
using MakeUnsigned = typename detail::MakeUnsignedBase<T>::Type;

/* conditional */

namespace detail {
    template<bool _cond, typename T, typename U>
    struct ConditionalBase {
        using Type = T;
    };

    template<typename T, typename U>
    struct ConditionalBase<false, T, U> {
        using Type = U;
    };
}

template<bool _cond, typename T, typename U>
using Conditional = typename detail::ConditionalBase<_cond, T, U>::Type;

/* result of call at compile time */

namespace detail {
#define OSTD_FWD(T, _v) static_cast<T &&>(_v)
    template<typename F, typename ...A>
    inline auto rof_invoke(F &&f, A &&...args) ->
      decltype(OSTD_FWD(F, f)(OSTD_FWD(A, args)...)) {
        return OSTD_FWD(F, f)(OSTD_FWD(A, args)...);
    }
    template<typename B, typename T, typename D>
    inline auto rof_invoke(T B::*pmd, D &&ref) ->
      decltype(OSTD_FWD(D, ref).*pmd) {
        return OSTD_FWD(D, ref).*pmd;
    }
    template<typename PMD, typename P>
    inline auto rof_invoke(PMD &&pmd, P &&ptr) ->
      decltype((*OSTD_FWD(P, ptr)).*OSTD_FWD(PMD, pmd)) {
        return (*OSTD_FWD(P, ptr)).*OSTD_FWD(PMD, pmd);
    }
    template<typename B, typename T, typename D, typename ...A>
    inline auto rof_invoke(T B::*pmf, D &&ref, A &&...args) ->
      decltype((OSTD_FWD(D, ref).*pmf)(OSTD_FWD(A, args)...)) {
        return (OSTD_FWD(D, ref).*pmf)(OSTD_FWD(A, args)...);
    }
    template<typename PMF, typename P, typename ...A>
    inline auto rof_invoke(PMF &&pmf, P &&ptr, A &&...args) ->
      decltype(((*OSTD_FWD(P, ptr)).*OSTD_FWD(PMF, pmf))
          (OSTD_FWD(A, args)...)) {
        return ((*OSTD_FWD(P, ptr)).*OSTD_FWD(PMF, pmf))
          (OSTD_FWD(A, args)...);
    }
#undef OSTD_FWD

    template<typename, typename = void>
    struct ResultOfCore {};
    template<typename F, typename ...A>
    struct ResultOfCore<F(A...), decltype(void(rof_invoke(
    detail::declval_in<F>(), detail::declval_in<A>()...)))> {
        using type = decltype(rof_invoke(detail::declval_in<F>(),
            detail::declval_in<A>()...));
    };

    template<typename T> struct ResultOfBase: ResultOfCore<T> {};
} /* namespace detail */

template<typename T>
using ResultOf = typename detail::ResultOfBase<T>::Type;

/* enable if */

namespace detail {
    template<bool B, typename T = void> struct EnableIfBase {};

    template<typename T> struct EnableIfBase<true, T> { using Type = T; };
}

template<bool B, typename T = void>
using EnableIf = typename detail::EnableIfBase<B, T>::Type;

/* decay */

namespace detail {
    template<typename T>
    struct DecayBase {
    private:
        using U = RemoveReference<T>;
    public:
        using Type = Conditional<IsArray<U>,
            RemoveExtent<U> *,
            Conditional<IsFunction<U>, AddPointer<U>, RemoveCv<U>>
        >;
    };
}

template<typename T>
using Decay = typename detail::DecayBase<T>::Type;

/* common type */

namespace detail {
    template<typename ...T> struct CommonTypeBase;

    template<typename T> struct CommonTypeBase<T> {
        using Type = Decay<T>;
    };

    template<typename T, typename U> struct CommonTypeBase<T, U> {
        using Type = Decay<decltype(true ? detail::declval_in<T>()
            : detail::declval_in<U>())>;
    };

    template<typename T, typename U, typename ...V>
    struct CommonTypeBase<T, U, V...> {
        using Type = typename CommonTypeBase<
            typename CommonTypeBase<T, U>::Type, V...
        >::Type;
    };
}

template<typename T, typename U, typename ...V>
using CommonType = typename detail::CommonTypeBase<T, U, V...>::Type;

/* aligned storage */

namespace detail {
    template<Size N> struct AlignedTest {
        union Type {
            byte data[N];
            MaxAlign align;
        };
    };

    template<Size N, Size A> struct AlignedStorageBase {
        struct Type {
            alignas(A) byte data[N];
        };
    };
}

template<Size N, Size A
    = alignof(typename detail::AlignedTest<N>::Type)
> using AlignedStorage = typename detail::AlignedStorageBase<N, A>::Type;

/* aligned union */

namespace detail {
    template<Size ...N> constexpr Size AlignMax = 0;
    template<Size N> constexpr Size AlignMax<N> = N;

    template<Size N1, Size N2> constexpr Size AlignMax<N1, N2>
        = (N1 > N2) ? N1 : N2;

    template<Size N1, Size N2, Size ...N>
    constexpr Size AlignMax<N1, N2, N...> = AlignMax<AlignMax<N1, N2>, N...>;

    template<Size N, typename ...T> struct AlignedUnionBase {
        static constexpr Size alignment_value
            = AlignMax<alignof(T)...>;

        struct type {
            alignas(alignment_value) byte data[AlignMax<N, sizeof(T)...>];
        };
    };
} /* namespace detail */

template<Size N, typename ...T>
using AlignedUnion = typename detail::AlignedUnionBase<N, T...>::Type;

/* underlying type */

namespace detail {
    /* gotta wrap, in a struct otherwise clang ICEs... */
    template<typename T> struct UnderlyingTypeBase {
        using Type = __underlying_type(T);
    };
}

template<typename T>
using UnderlyingType = typename detail::UnderlyingTypeBase<T>::Type;

} /* namespace ostd */

#endif