include/tuple

// -*- C++ -*-
//===--------------------------- tuple ------------------------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#ifndef _LIBCPP_TUPLE
#define _LIBCPP_TUPLE

/*
    tuple synopsis

namespace std
{

template <class... T>
class tuple {
public:
    constexpr tuple();
    explicit tuple(const T&...);
    template <class... U>
        explicit tuple(U&&...);
    tuple(const tuple&) = default;
    tuple(tuple&&);
    template <class... U>
        tuple(const tuple<U...>&);
    template <class... U>
        tuple(tuple<U...>&&);
    template <class U1, class U2>
        tuple(const pair<U1, U2>&); // iff sizeof...(T) == 2
    template <class U1, class U2>
        tuple(pair<U1, U2>&&); // iff sizeof...(T) == 2

    // allocator-extended constructors
    template <class Alloc>
        tuple(allocator_arg_t, const Alloc& a);
    template <class Alloc>
        tuple(allocator_arg_t, const Alloc& a, const T&...);
    template <class Alloc, class... U>
        tuple(allocator_arg_t, const Alloc& a, U&&...);
    template <class Alloc>
        tuple(allocator_arg_t, const Alloc& a, const tuple&);
    template <class Alloc>
        tuple(allocator_arg_t, const Alloc& a, tuple&&);
    template <class Alloc, class... U>
        tuple(allocator_arg_t, const Alloc& a, const tuple<U...>&);
    template <class Alloc, class... U>
        tuple(allocator_arg_t, const Alloc& a, tuple<U...>&&);
    template <class Alloc, class U1, class U2>
        tuple(allocator_arg_t, const Alloc& a, const pair<U1, U2>&);
    template <class Alloc, class U1, class U2>
        tuple(allocator_arg_t, const Alloc& a, pair<U1, U2>&&);

    tuple& operator=(const tuple&);
    tuple& operator=(tuple&&);
    template <class... U>
        tuple& operator=(const tuple<U...>&);
    template <class... U>
        tuple& operator=(tuple<U...>&&);
    template <class U1, class U2>
        tuple& operator=(const pair<U1, U2>&); // iff sizeof...(T) == 2
    template <class U1, class U2>
        tuple& operator=(pair<U1, U2>&&); //iffsizeof...(T) == 2

    void swap(tuple&);
};

const unspecified ignore;

template <class... T> tuple<V...>  make_tuple(T&&...);
template <class... T> tuple<ATypes...> forward_as_tuple(T&&...);
template <class... T> tuple<T&...> tie(T&...);
template <class... T, class... U> tuple<T..., U...> tuple_cat(const tuple<T...>&, const tuple<U...>&);
template <class... T, class... U> tuple<T..., U...> tuple_cat(tuple<T...>&&, const tuple<U...>&);
template <class... T, class... U> tuple<T..., U...> tuple_cat(const tuple<T...>&, tuple<U...>&&);
template <class... T, class... U> tuple<T..., U...> tuple_cat(tuple<T...>&&, tuple<U...>&&);

// 20.4.1.4, tuple helper classes:
template <class T> class tuple_size; // undefined
template <class... T> class tuple_size<tuple<T...>>;
template <intsize_t I, class T> class tuple_element; // undefined
template <intsize_t I, class... T> class tuple_element<I, tuple<T...>>;

// 20.4.1.5, element access:
template <intsize_t I, class... T> typename tuple_element<I, tuple<T...>>::type& get(tuple<T...>&);
template <intsize_t I, class... T> typename tuple_element<I, tuple<T...>>::type const& get(const tuple<T...>&);

// 20.4.1.6, relational operators:
template<class... T, class... U> bool operator==(const tuple<T...>&, const tuple<U...>&);
template<class... T, class... U> bool operator<(const tuple<T...>&, const tuple<U...>&);
template<class... T, class... U> bool operator!=(const tuple<T...>&, const tuple<U...>&);
template<class... T, class... U> bool operator>(const tuple<T...>&, const tuple<U...>&);
template<class... T, class... U> bool operator<=(const tuple<T...>&, const tuple<U...>&);
template<class... T, class... U> bool operator>=(const tuple<T...>&, const tuple<U...>&);

template <class... Types, class Alloc>
  struct uses_allocator<tuple<Types...>, Alloc>;

template <class... Types>
  void swap(tuple<Types...>& x, tuple<Types...>& y);

}  // std

*/

#include <__config>
#include <__tuple>
#include <cstddef>
#include <memory>
#include <type_traits>

#pragma GCC system_header

_LIBCPP_BEGIN_NAMESPACE_STD

#ifndef _LIBCPP_HAS_NO_VARIADICS

// tuple_size

template <class ..._Tp>
class _LIBCPP_VISIBLE tuple_size<tuple<_Tp...>>
    : public integral_constant<size_t, sizeof...(_Tp)>
{
};

template <class ..._Tp>
class _LIBCPP_VISIBLE tuple_size<const tuple<_Tp...>>
    : public integral_constant<size_t, sizeof...(_Tp)>
{
};

// tuple_element

template <size_t _Ip, class ..._Tp>
class _LIBCPP_VISIBLE tuple_element<_Ip, tuple<_Tp...>>
{
public:
    typedef typename tuple_element<_Ip, __tuple_types<_Tp...>>::type type;
};

template <size_t _Ip, class ..._Tp>
class _LIBCPP_VISIBLE tuple_element<_Ip, const tuple<_Tp...>>
{
public:
    typedef const typename tuple_element<_Ip, __tuple_types<_Tp...>>::type type;
};

// __tuple_leaf

template <size_t _Ip, class _Hp, bool=is_empty<_Hp>::value>
class __tuple_leaf;

template <size_t _Ip, class _Hp, bool _Ep>
inline _LIBCPP_INLINE_VISIBILITY
void swap(__tuple_leaf<_Ip, _Hp, _Ep>& __x, __tuple_leaf<_Ip, _Hp, _Ep>& __y)
{
    swap(__x.get(), __y.get());
}

template <size_t _Ip, class _Hp, bool>
class __tuple_leaf
{
    _Hp value;

    __tuple_leaf& operator=(const __tuple_leaf&);
public:
    _LIBCPP_INLINE_VISIBILITY __tuple_leaf() : value()
       {static_assert(!is_reference<_Hp>::value,
              "Attempted to default construct a reference element in a tuple");}

    template <class _Alloc>
        _LIBCPP_INLINE_VISIBILITY
        __tuple_leaf(integral_constant<int, 0>, const _Alloc&)
            : value()
        {static_assert(!is_reference<_Hp>::value,
              "Attempted to default construct a reference element in a tuple");}

    template <class _Alloc>
        _LIBCPP_INLINE_VISIBILITY
        __tuple_leaf(integral_constant<int, 1>, const _Alloc& __a)
            : value(allocator_arg_t(), __a)
        {static_assert(!is_reference<_Hp>::value,
              "Attempted to default construct a reference element in a tuple");}

    template <class _Alloc>
        _LIBCPP_INLINE_VISIBILITY
        __tuple_leaf(integral_constant<int, 2>, const _Alloc& __a)
            : value(__a)
        {static_assert(!is_reference<_Hp>::value,
              "Attempted to default construct a reference element in a tuple");}

    template <class _Tp>
        _LIBCPP_INLINE_VISIBILITY
        explicit __tuple_leaf(_Tp&& __t)
            : value(_STD::forward<_Tp>(__t))
        {static_assert(!is_lvalue_reference<_Hp>::value ||
                        is_lvalue_reference<_Hp>::value &&
                        (is_lvalue_reference<_Tp>::value ||
                         is_same<typename remove_reference<_Tp>::type,
                                 reference_wrapper<
                                    typename remove_reference<_Hp>::type
                                 >
                                >::value),
       "Attempted to construct a reference element in a tuple with an rvalue");}

    template <class _Tp, class _Alloc>
        _LIBCPP_INLINE_VISIBILITY
        explicit __tuple_leaf(integral_constant<int, 0>, const _Alloc&, _Tp&& __t)
            : value(_STD::forward<_Tp>(__t))
        {static_assert(!is_lvalue_reference<_Hp>::value ||
                        is_lvalue_reference<_Hp>::value &&
                        (is_lvalue_reference<_Tp>::value ||
                         is_same<typename remove_reference<_Tp>::type,
                                 reference_wrapper<
                                    typename remove_reference<_Hp>::type
                                 >
                                >::value),
       "Attempted to construct a reference element in a tuple with an rvalue");}

    template <class _Tp, class _Alloc>
        _LIBCPP_INLINE_VISIBILITY
        explicit __tuple_leaf(integral_constant<int, 1>, const _Alloc& __a, _Tp&& __t)
            : value(allocator_arg_t(), __a, _STD::forward<_Tp>(__t))
        {static_assert(!is_lvalue_reference<_Hp>::value ||
                        is_lvalue_reference<_Hp>::value &&
                        (is_lvalue_reference<_Tp>::value ||
                         is_same<typename remove_reference<_Tp>::type,
                                 reference_wrapper<
                                    typename remove_reference<_Hp>::type
                                 >
                                >::value),
       "Attempted to construct a reference element in a tuple with an rvalue");}

    template <class _Tp, class _Alloc>
        _LIBCPP_INLINE_VISIBILITY
        explicit __tuple_leaf(integral_constant<int, 2>, const _Alloc& __a, _Tp&& __t)
            : value(_STD::forward<_Tp>(__t), __a)
        {static_assert(!is_lvalue_reference<_Hp>::value ||
                        is_lvalue_reference<_Hp>::value &&
                        (is_lvalue_reference<_Tp>::value ||
                         is_same<typename remove_reference<_Tp>::type,
                                 reference_wrapper<
                                    typename remove_reference<_Hp>::type
                                 >
                                >::value),
       "Attempted to construct a reference element in a tuple with an rvalue");}

    template <class _Tp>
        _LIBCPP_INLINE_VISIBILITY
        explicit __tuple_leaf(const __tuple_leaf<_Ip, _Tp>& __t)
            : value(__t.get()) {}

    template <class _Tp>
        _LIBCPP_INLINE_VISIBILITY
        __tuple_leaf&
        operator=(_Tp&& __t)
        {
            value = _STD::forward<_Tp>(__t);
            return *this;
        }

    _LIBCPP_INLINE_VISIBILITY
    int swap(__tuple_leaf& __t)
    {
        _STD::swap(*this, __t);
        return 0;
    }

    _LIBCPP_INLINE_VISIBILITY       _Hp& get()       {return value;}
    _LIBCPP_INLINE_VISIBILITY const _Hp& get() const {return value;}
};

template <size_t _Ip, class _Hp>
class __tuple_leaf<_Ip, _Hp, true>
    : private _Hp
{

    __tuple_leaf& operator=(const __tuple_leaf&);
public:
    _LIBCPP_INLINE_VISIBILITY __tuple_leaf() {}

    template <class _Alloc>
        _LIBCPP_INLINE_VISIBILITY
        __tuple_leaf(integral_constant<int, 0>, const _Alloc&) {}

    template <class _Alloc>
        _LIBCPP_INLINE_VISIBILITY
        __tuple_leaf(integral_constant<int, 1>, const _Alloc& __a)
            : _Hp(allocator_arg_t(), __a) {}

    template <class _Alloc>
        _LIBCPP_INLINE_VISIBILITY
        __tuple_leaf(integral_constant<int, 2>, const _Alloc& __a)
            : _Hp(__a) {}

    template <class _Tp>
        _LIBCPP_INLINE_VISIBILITY
        explicit __tuple_leaf(_Tp&& __t)
            : _Hp(_STD::forward<_Tp>(__t)) {}

    template <class _Tp, class _Alloc>
        _LIBCPP_INLINE_VISIBILITY
        explicit __tuple_leaf(integral_constant<int, 0>, const _Alloc&, _Tp&& __t)
            : _Hp(_STD::forward<_Tp>(__t)) {}

    template <class _Tp, class _Alloc>
        _LIBCPP_INLINE_VISIBILITY
        explicit __tuple_leaf(integral_constant<int, 1>, const _Alloc& __a, _Tp&& __t)
            : _Hp(allocator_arg_t(), __a, _STD::forward<_Tp>(__t)) {}

    template <class _Tp, class _Alloc>
        _LIBCPP_INLINE_VISIBILITY
        explicit __tuple_leaf(integral_constant<int, 2>, const _Alloc& __a, _Tp&& __t)
            : _Hp(_STD::forward<_Tp>(__t), __a) {}

    template <class _Tp>
        _LIBCPP_INLINE_VISIBILITY
        explicit __tuple_leaf(const __tuple_leaf<_Ip, _Tp>& __t)
            : _Hp(__t.get()) {}

    template <class _Tp>
        _LIBCPP_INLINE_VISIBILITY
        __tuple_leaf&
        operator=(_Tp&& __t)
        {
            _Hp::operator=(_STD::forward<_Tp>(__t));
            return *this;
        }

    _LIBCPP_INLINE_VISIBILITY int swap(__tuple_leaf& __t)
    {
        _STD::swap(*this, __t);
        return 0;
    }

    _LIBCPP_INLINE_VISIBILITY       _Hp& get()       {return static_cast<_Hp&>(*this);}
    _LIBCPP_INLINE_VISIBILITY const _Hp& get() const {return static_cast<const _Hp&>(*this);}
};

template <class ..._Tp>
_LIBCPP_INLINE_VISIBILITY
void __swallow(_Tp&&...) {}

// __tuple_impl

template<class _Indx, class ..._Tp> struct __tuple_impl;

template<size_t ..._Indx, class ..._Tp>
struct __tuple_impl<__tuple_indices<_Indx...>, _Tp...>
    : public __tuple_leaf<_Indx, _Tp>...
{
    template <size_t ..._Uf, class ..._Tf,
              size_t ..._Ul, class ..._Tl, class ..._Up>
        _LIBCPP_INLINE_VISIBILITY
        explicit
        __tuple_impl(__tuple_indices<_Uf...>, __tuple_types<_Tf...>,
                     __tuple_indices<_Ul...>, __tuple_types<_Tl...>,
                     _Up&&... __u) :
            __tuple_leaf<_Uf, _Tf>(_STD::forward<_Up>(__u))...,
            __tuple_leaf<_Ul, _Tl>()...
            {}

    template <class _Alloc, size_t ..._Uf, class ..._Tf,
              size_t ..._Ul, class ..._Tl, class ..._Up>
        _LIBCPP_INLINE_VISIBILITY
        explicit
        __tuple_impl(allocator_arg_t, const _Alloc& __a,
                     __tuple_indices<_Uf...>, __tuple_types<_Tf...>,
                     __tuple_indices<_Ul...>, __tuple_types<_Tl...>,
                     _Up&&... __u) :
            __tuple_leaf<_Uf, _Tf>(__uses_alloc_ctor<_Tf, _Alloc, _Up>(), __a,
            _STD::forward<_Up>(__u))...,
            __tuple_leaf<_Ul, _Tl>(__uses_alloc_ctor<_Tl, _Alloc>(), __a)...
            {}

    template <class _Tuple,
              class = typename enable_if
                      <
                         __tuple_convertible<_Tuple, tuple<_Tp...>>::value
                      >::type
             >
        _LIBCPP_INLINE_VISIBILITY
        __tuple_impl(_Tuple&& __t)
            : __tuple_leaf<_Indx, _Tp>(_STD::forward<typename tuple_element<_Indx,
                                       typename __make_tuple_types<_Tuple>::type>::type>(_STD::get<_Indx>(__t)))...
            {}

    template <class _Alloc, class _Tuple,
              class = typename enable_if
                      <
                         __tuple_convertible<_Tuple, tuple<_Tp...>>::value
                      >::type
             >
        _LIBCPP_INLINE_VISIBILITY
        __tuple_impl(allocator_arg_t, const _Alloc& __a, _Tuple&& __t)
            : __tuple_leaf<_Indx, _Tp>(__uses_alloc_ctor<_Tp, _Alloc, typename tuple_element<_Indx,
                                       typename __make_tuple_types<_Tuple>::type>::type>(), __a,
                                       _STD::forward<typename tuple_element<_Indx,
                                       typename __make_tuple_types<_Tuple>::type>::type>(_STD::get<_Indx>(__t)))...
            {}

    template <class _Tuple>
        _LIBCPP_INLINE_VISIBILITY
        typename enable_if
        <
            __tuple_assignable<_Tuple, tuple<_Tp...>>::value,
            __tuple_impl&
        >::type
        operator=(_Tuple&& __t)
        {
            __swallow(__tuple_leaf<_Indx, _Tp>::operator=(_STD::forward<typename tuple_element<_Indx,
                                       typename __make_tuple_types<_Tuple>::type>::type>(_STD::get<_Indx>(__t)))...);
            return *this;
        }

    _LIBCPP_INLINE_VISIBILITY
    void swap(__tuple_impl& __t)
    {
        __swallow(__tuple_leaf<_Indx, _Tp>::swap(static_cast<__tuple_leaf<_Indx, _Tp>&>(__t))...);
    }
};

template <class ..._Tp>
class _LIBCPP_VISIBLE tuple
{
    typedef __tuple_impl<typename __make_tuple_indices<sizeof...(_Tp)>::type, _Tp...> base;

    base base_;

    template <size_t _Jp, class ..._Up> friend
        typename tuple_element<_Jp, tuple<_Up...>>::type& get(tuple<_Up...>&);
    template <size_t _Jp, class ..._Up> friend
        const typename tuple_element<_Jp, tuple<_Up...>>::type& get(const tuple<_Up...>&);
public:

    _LIBCPP_INLINE_VISIBILITY
    explicit tuple(const _Tp& ... __t)
        : base_(typename __make_tuple_indices<sizeof...(_Tp)>::type(),
                typename __make_tuple_types<tuple, sizeof...(_Tp)>::type(),
                typename __make_tuple_indices<0>::type(),
                typename __make_tuple_types<tuple, 0>::type(),
                __t...
               ) {}

    template <class _Alloc>
      _LIBCPP_INLINE_VISIBILITY
      tuple(allocator_arg_t, const _Alloc& __a, const _Tp& ... __t)
        : base_(allocator_arg_t(), __a,
                typename __make_tuple_indices<sizeof...(_Tp)>::type(),
                typename __make_tuple_types<tuple, sizeof...(_Tp)>::type(),
                typename __make_tuple_indices<0>::type(),
                typename __make_tuple_types<tuple, 0>::type(),
                __t...
               ) {}

    template <class ..._Up,
              class = typename enable_if
                      <
                         sizeof...(_Up) <= sizeof...(_Tp) &&
                         __tuple_convertible
                         <
                            tuple<_Up...>,
                            typename __make_tuple_types<tuple,
                                     sizeof...(_Up) < sizeof...(_Tp) ?
                                        sizeof...(_Up) :
                                        sizeof...(_Tp)>::type
                         >::value
                      >::type
             >
        _LIBCPP_INLINE_VISIBILITY
        explicit
        tuple(_Up&&... __u)
            : base_(typename __make_tuple_indices<sizeof...(_Up)>::type(),
                    typename __make_tuple_types<tuple, sizeof...(_Up)>::type(),
                    typename __make_tuple_indices<sizeof...(_Tp), sizeof...(_Up)>::type(),
                    typename __make_tuple_types<tuple, sizeof...(_Tp), sizeof...(_Up)>::type(),
                    _STD::forward<_Up>(__u)...) {}

    template <class _Alloc, class ..._Up,
              class = typename enable_if
                      <
                         sizeof...(_Up) <= sizeof...(_Tp) &&
                         __tuple_convertible
                         <
                            tuple<_Up...>,
                            typename __make_tuple_types<tuple,
                                     sizeof...(_Up) < sizeof...(_Tp) ?
                                        sizeof...(_Up) :
                                        sizeof...(_Tp)>::type
                         >::value
                      >::type
             >
        _LIBCPP_INLINE_VISIBILITY
        tuple(allocator_arg_t, const _Alloc& __a, _Up&&... __u)
            : base_(allocator_arg_t(), __a,
                    typename __make_tuple_indices<sizeof...(_Up)>::type(),
                    typename __make_tuple_types<tuple, sizeof...(_Up)>::type(),
                    typename __make_tuple_indices<sizeof...(_Tp), sizeof...(_Up)>::type(),
                    typename __make_tuple_types<tuple, sizeof...(_Tp), sizeof...(_Up)>::type(),
                    _STD::forward<_Up>(__u)...) {}

    template <class _Tuple,
              class = typename enable_if
                      <
                         __tuple_convertible<_Tuple, tuple>::value
                      >::type
             >
        _LIBCPP_INLINE_VISIBILITY
        tuple(_Tuple&& __t)
            : base_(_STD::forward<_Tuple>(__t)) {}

    template <class _Alloc, class _Tuple,
              class = typename enable_if
                      <
                         __tuple_convertible<_Tuple, tuple>::value
                      >::type
             >
        _LIBCPP_INLINE_VISIBILITY
        tuple(allocator_arg_t, const _Alloc& __a, _Tuple&& __t)
            : base_(allocator_arg_t(), __a, _STD::forward<_Tuple>(__t)) {}

    template <class _Tuple,
              class = typename enable_if
                      <
                         __tuple_assignable<_Tuple, tuple>::value
                      >::type
             >
        _LIBCPP_INLINE_VISIBILITY
        tuple&
        operator=(_Tuple&& __t)
        {
            base_.operator=(_STD::forward<_Tuple>(__t));
            return *this;
        }

    _LIBCPP_INLINE_VISIBILITY
    void swap(tuple& __t) {base_.swap(__t.base_);}
};

template <>
class _LIBCPP_VISIBLE tuple<>
{
public:
    _LIBCPP_INLINE_VISIBILITY
    tuple() {}
    template <class _Alloc>
    _LIBCPP_INLINE_VISIBILITY
        tuple(allocator_arg_t, const _Alloc&) {}
    template <class _Alloc>
    _LIBCPP_INLINE_VISIBILITY
        tuple(allocator_arg_t, const _Alloc&, const tuple&) {}
    template <class _U>
    _LIBCPP_INLINE_VISIBILITY
        tuple(array<_U, 0>) {}
    template <class _Alloc, class _U>
    _LIBCPP_INLINE_VISIBILITY
        tuple(allocator_arg_t, const _Alloc&, array<_U, 0>) {}
    _LIBCPP_INLINE_VISIBILITY
    void swap(tuple&) {}
};

template <class ..._Tp>
inline _LIBCPP_INLINE_VISIBILITY
void
swap(tuple<_Tp...>& __t, tuple<_Tp...>& __u) {__t.swap(__u);}

// get

template <size_t _Ip, class ..._Tp>
inline _LIBCPP_INLINE_VISIBILITY
typename tuple_element<_Ip, tuple<_Tp...>>::type&
get(tuple<_Tp...>& __t)
{
    typedef typename tuple_element<_Ip, tuple<_Tp...>>::type type;
    return static_cast<__tuple_leaf<_Ip, type>&>(__t.base_).get();
}

template <size_t _Ip, class ..._Tp>
inline _LIBCPP_INLINE_VISIBILITY
const typename tuple_element<_Ip, tuple<_Tp...>>::type&
get(const tuple<_Tp...>& __t)
{
    typedef typename tuple_element<_Ip, tuple<_Tp...>>::type type;
    return static_cast<const __tuple_leaf<_Ip, type>&>(__t.base_).get();
}

// tie

template <class ..._Tp>
inline _LIBCPP_INLINE_VISIBILITY
tuple<_Tp&...>
tie(_Tp&... __t)
{
    return tuple<_Tp&...>(__t...);
}

template <class _Up>
struct __ignore_t
{
    _LIBCPP_INLINE_VISIBILITY
    __ignore_t() {}
    template <class _Tp>
        _LIBCPP_INLINE_VISIBILITY
        __ignore_t(_Tp&&) {}
    template <class _Tp>
        _LIBCPP_INLINE_VISIBILITY
        const __ignore_t& operator=(_Tp&&) const {return *this;}
};

namespace { const __ignore_t<unsigned char> ignore = __ignore_t<unsigned char>(); }

template <class _Tp> class reference_wrapper;

template <class _Tp>
struct ___make_tuple_return
{
    typedef _Tp type;
};

template <class _Tp>
struct ___make_tuple_return<reference_wrapper<_Tp>>
{
    typedef _Tp& type;
};

template <class _Tp>
struct __make_tuple_return
{
    typedef typename ___make_tuple_return<typename decay<_Tp>::type>::type type;
};

template <class... _Tp>
inline _LIBCPP_INLINE_VISIBILITY
tuple<typename __make_tuple_return<_Tp>::type...>
make_tuple(_Tp&&... __t)
{
    return tuple<typename __make_tuple_return<_Tp>::type...>(_STD::forward<_Tp>(__t)...);
}

template <class... _Tp>
inline _LIBCPP_INLINE_VISIBILITY
tuple<_Tp&&...>
forward_as_tuple(_Tp&&... __t)
{
    return tuple<_Tp&&...>(_STD::forward<_Tp>(__t)...);
}

template <size_t _I>
struct __tuple_equal
{
    template <class _Tp, class _Up>
    _LIBCPP_INLINE_VISIBILITY
    bool operator()(const _Tp& __x, const _Up& __y)
    {
        return __tuple_equal<_I - 1>()(__x, __y) && get<_I-1>(__x) == get<_I-1>(__y);
    }
};

template <>
struct __tuple_equal<0>
{
    template <class _Tp, class _Up>
    _LIBCPP_INLINE_VISIBILITY
    bool operator()(const _Tp&, const _Up&)
    {
        return true;
    }
};

template <class ..._Tp, class ..._Up>
inline _LIBCPP_INLINE_VISIBILITY
bool
operator==(const tuple<_Tp...>& __x, const tuple<_Up...>& __y)
{
    return __tuple_equal<sizeof...(_Tp)>()(__x, __y);
}

template <class ..._Tp, class ..._Up>
inline _LIBCPP_INLINE_VISIBILITY
bool
operator!=(const tuple<_Tp...>& __x, const tuple<_Up...>& __y)
{
    return !(__x == __y);
}

template <size_t _I>
struct __tuple_less
{
    template <class _Tp, class _Up>
    _LIBCPP_INLINE_VISIBILITY
    bool operator()(const _Tp& __x, const _Up& __y)
    {
        return __tuple_less<_I-1>()(__x, __y) ||
             (!__tuple_less<_I-1>()(__y, __x) && get<_I-1>(__x) < get<_I-1>(__y));
    }
};

template <>
struct __tuple_less<0>
{
    template <class _Tp, class _Up>
    _LIBCPP_INLINE_VISIBILITY
    bool operator()(const _Tp&, const _Up&)
    {
        return false;
    }
};

template <class ..._Tp, class ..._Up>
inline _LIBCPP_INLINE_VISIBILITY
bool
operator<(const tuple<_Tp...>& __x, const tuple<_Up...>& __y)
{
    return __tuple_less<sizeof...(_Tp)>()(__x, __y);
}

template <class ..._Tp, class ..._Up>
inline _LIBCPP_INLINE_VISIBILITY
bool
operator>(const tuple<_Tp...>& __x, const tuple<_Up...>& __y)
{
    return __y < __x;
}

template <class ..._Tp, class ..._Up>
inline _LIBCPP_INLINE_VISIBILITY
bool
operator>=(const tuple<_Tp...>& __x, const tuple<_Up...>& __y)
{
    return !(__x < __y);
}

template <class ..._Tp, class ..._Up>
inline _LIBCPP_INLINE_VISIBILITY
bool
operator<=(const tuple<_Tp...>& __x, const tuple<_Up...>& __y)
{
    return !(__y < __x);
}

// tuple_cat

template <class... _Tp, size_t ..._I1, class... _Up, size_t ..._I2>
inline _LIBCPP_INLINE_VISIBILITY
tuple<_Tp..., _Up...>
__tuple_cat(const tuple<_Tp...>& __x, __tuple_indices<_I1...>, const tuple<_Up...>& __y, __tuple_indices<_I2...>)
{
    return tuple<_Tp..., _Up...>(get<_I1>(__x)..., get<_I2>(__y)...);
}

template <class... _Tp, class... _Up>
inline _LIBCPP_INLINE_VISIBILITY
tuple<_Tp..., _Up...>
tuple_cat(const tuple<_Tp...>& __x, const tuple<_Up...>& __y)
{
    return __tuple_cat(__x, typename __make_tuple_indices<sizeof...(_Tp)>::type(),
                       __y, typename __make_tuple_indices<sizeof...(_Up)>::type());
}

template <class... _Tp, size_t ..._I1, class... _Up, size_t ..._I2>
inline _LIBCPP_INLINE_VISIBILITY
tuple<_Tp..., _Up...>
__tuple_cat(tuple<_Tp...>&& __x, __tuple_indices<_I1...>, const tuple<_Up...>& __y, __tuple_indices<_I2...>)
{
    return tuple<_Tp..., _Up...>(_STD::forward<_Tp>(get<_I1>(__x))..., get<_I2>(__y)...);
}

template <class... _Tp, class... _Up>
inline _LIBCPP_INLINE_VISIBILITY
tuple<_Tp..., _Up...>
tuple_cat(tuple<_Tp...>&& __x, const tuple<_Up...>& __y)
{
    return __tuple_cat(_STD::move(__x), typename __make_tuple_indices<sizeof...(_Tp)>::type(),
                       __y, typename __make_tuple_indices<sizeof...(_Up)>::type());
}

template <class... _Tp, size_t ..._I1, class... _Up, size_t ..._I2>
inline _LIBCPP_INLINE_VISIBILITY
tuple<_Tp..., _Up...>
__tuple_cat(const tuple<_Tp...>& __x, __tuple_indices<_I1...>, tuple<_Up...>&& __y, __tuple_indices<_I2...>)
{
    return tuple<_Tp..., _Up...>(get<_I1>(__x)..., _STD::forward<_Up>(get<_I2>(__y))...);
}

template <class... _Tp, class... _Up>
inline _LIBCPP_INLINE_VISIBILITY
tuple<_Tp..., _Up...>
tuple_cat(const tuple<_Tp...>& __x, tuple<_Up...>&& __y)
{
    return __tuple_cat(__x, typename __make_tuple_indices<sizeof...(_Tp)>::type(),
                       _STD::move(__y), typename __make_tuple_indices<sizeof...(_Up)>::type());
}

template <class... _Tp, size_t ..._I1, class... _Up, size_t ..._I2>
inline _LIBCPP_INLINE_VISIBILITY
tuple<_Tp..., _Up...>
__tuple_cat(tuple<_Tp...>&& __x, __tuple_indices<_I1...>, tuple<_Up...>&& __y, __tuple_indices<_I2...>)
{
    return tuple<_Tp..., _Up...>(_STD::forward<_Tp>(get<_I1>(__x))..., _STD::forward<_Up>(get<_I2>(__y))...);
}

template <class... _Tp, class... _Up>
inline _LIBCPP_INLINE_VISIBILITY
tuple<_Tp..., _Up...>
tuple_cat(tuple<_Tp...>&& __x, tuple<_Up...>&& __y)
{
    return __tuple_cat(_STD::move(__x), typename __make_tuple_indices<sizeof...(_Tp)>::type(),
                       _STD::move(__y), typename __make_tuple_indices<sizeof...(_Up)>::type());
}

template <class ..._Tp, class _Alloc>
struct _LIBCPP_VISIBLE uses_allocator<tuple<_Tp...>, _Alloc>
    : true_type {};

template <class _T1, class _T2>
template <class... _Args1, class... _Args2, size_t ..._I1, size_t ..._I2>
inline _LIBCPP_INLINE_VISIBILITY
pair<_T1, _T2>::pair(piecewise_construct_t,
                     tuple<_Args1...>& __first_args, tuple<_Args2...>& __second_args,
                     __tuple_indices<_I1...>, __tuple_indices<_I2...>)
    :  first(_STD::forward<_Args1>(get<_I1>( __first_args))...),
      second(_STD::forward<_Args2>(get<_I2>(__second_args))...)
{
}

#endif  // _LIBCPP_HAS_NO_VARIADICS

_LIBCPP_END_NAMESPACE_STD

#endif  // _LIBCPP_TUPLE