Add libc++ and libc++abi to third-party.

third_party/libcxx/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&...);  // constexpr in C++14
+    template <class... U>
+        explicit tuple(U&&...);  // constexpr in C++14
+    tuple(const tuple&) = default;
+    tuple(tuple&&) = default;
+    template <class... U>
+        tuple(const tuple<U...>&);  // constexpr in C++14
+    template <class... U>
+        tuple(tuple<U...>&&);  // constexpr in C++14
+    template <class U1, class U2>
+        tuple(const pair<U1, U2>&); // iff sizeof...(T) == 2 // constexpr in C++14
+    template <class U1, class U2>
+        tuple(pair<U1, U2>&&); // iff sizeof...(T) == 2  // constexpr in C++14
+
+    // 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&&) noexcept(AND(is_nothrow_move_assignable<T>::value ...));
+    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&) noexcept(AND(swap(declval<T&>(), declval<T&>())...));
+};
+
+const unspecified ignore;
+
+template <class... T> tuple<V...>  make_tuple(T&&...); // constexpr in C++14
+template <class... T> tuple<ATypes...> forward_as_tuple(T&&...) noexcept; // constexpr in C++14
+template <class... T> tuple<T&...> tie(T&...) noexcept;
+template <class... Tuples> tuple<CTypes...> tuple_cat(Tuples&&... tpls); // constexpr in C++14
+  
+// 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...>&) noexcept; // constexpr in C++14
+template <intsize_t I, class... T>
+    typename tuple_element<I, tuple<T...>>::type const&
+    get(const tuple<T...>&) noexcept; // constexpr in C++14
+template <intsize_t I, class... T>
+    typename tuple_element<I, tuple<T...>>::type&&
+    get(tuple<T...>&&) noexcept; // constexpr in C++14
+
+template <class T1, class... T>
+    constexpr T1& get(tuple<T...>&) noexcept;  // C++14
+template <class T1, class... T>
+    constexpr T1 const& get(const tuple<T...>&) noexcept;   // C++14
+template <class T1, class... T>
+    constexpr T1&& get(tuple<T...>&&) noexcept;   // C++14
+
+// 20.4.1.6, relational operators:
+template<class... T, class... U> bool operator==(const tuple<T...>&, const tuple<U...>&); // constexpr in C++14
+template<class... T, class... U> bool operator<(const tuple<T...>&, const tuple<U...>&);  // constexpr in C++14
+template<class... T, class... U> bool operator!=(const tuple<T...>&, const tuple<U...>&); // constexpr in C++14
+template<class... T, class... U> bool operator>(const tuple<T...>&, const tuple<U...>&);  // constexpr in C++14
+template<class... T, class... U> bool operator<=(const tuple<T...>&, const tuple<U...>&); // constexpr in C++14
+template<class... T, class... U> bool operator>=(const tuple<T...>&, const tuple<U...>&); // constexpr in C++14
+
+template <class... Types, class Alloc>
+  struct uses_allocator<tuple<Types...>, Alloc>;
+
+template <class... Types>
+  void
+  swap(tuple<Types...>& x, tuple<Types...>& y) noexcept(noexcept(x.swap(y)));
+
+}  // std
+
+*/
+
+#include <__config>
+#include <__tuple>
+#include <cstddef>
+#include <type_traits>
+#include <__functional_base>
+#include <utility>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#ifndef _LIBCPP_HAS_NO_VARIADICS
+
+// tuple_size
+
+template <class ..._Tp>
+class _LIBCPP_TYPE_VIS_ONLY tuple_size<tuple<_Tp...> >
+    : public integral_constant<size_t, sizeof...(_Tp)>
+{
+};
+
+// tuple_element
+
+template <size_t _Ip, class ..._Tp>
+class _LIBCPP_TYPE_VIS_ONLY tuple_element<_Ip, tuple<_Tp...> >
+{
+public:
+    typedef typename tuple_element<_Ip, __tuple_types<_Tp...> >::type type;
+};
+
+// __tuple_leaf
+
+template <size_t _Ip, class _Hp, bool=is_empty<_Hp>::value
+#if __has_feature(is_final)
+                                 && !__is_final(_Hp)
+#endif
+         >
+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)
+    _NOEXCEPT_(__is_nothrow_swappable<_Hp>::value)
+{
+    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 _LIBCPP_CONSTEXPR __tuple_leaf()
+             _NOEXCEPT_(is_nothrow_default_constructible<_Hp>::value) : 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,
+              class = typename enable_if<is_constructible<_Hp, _Tp>::value>::type>
+        _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
+        explicit __tuple_leaf(_Tp&& __t) _NOEXCEPT_((is_nothrow_constructible<_Hp, _Tp>::value))
+            : value(_VSTD::forward<_Tp>(__t))
+        {static_assert(!is_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)) ||
+                        (is_rvalue_reference<_Hp>::value &&
+                         !is_lvalue_reference<_Tp>::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(_VSTD::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, _VSTD::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(_VSTD::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");}
+
+    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_CONSTEXPR_AFTER_CXX11
+    __tuple_leaf(const __tuple_leaf& __t) _NOEXCEPT_(is_nothrow_copy_constructible<_Hp>::value)
+        : value(__t.get())
+        {static_assert(!is_rvalue_reference<_Hp>::value, "Can not copy a tuple with rvalue reference member");}
+
+    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_CONSTEXPR_AFTER_CXX11
+    __tuple_leaf(__tuple_leaf&& __t) _NOEXCEPT_(is_nothrow_move_constructible<_Hp>::value)
+        : value(_VSTD::forward<_Hp>(__t.get()))
+        {}
+
+    template <class _Tp>
+        _LIBCPP_INLINE_VISIBILITY
+        __tuple_leaf&
+        operator=(_Tp&& __t) _NOEXCEPT_((is_nothrow_assignable<_Hp&, _Tp>::value))
+        {
+            value = _VSTD::forward<_Tp>(__t);
+            return *this;
+        }
+
+    _LIBCPP_INLINE_VISIBILITY
+    int swap(__tuple_leaf& __t) _NOEXCEPT_(__is_nothrow_swappable<__tuple_leaf>::value)
+    {
+        _VSTD::swap(*this, __t);
+        return 0;
+    }
+
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11       _Hp& get()       _NOEXCEPT {return value;}
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11 const _Hp& get() const _NOEXCEPT {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 _LIBCPP_CONSTEXPR __tuple_leaf()
+             _NOEXCEPT_(is_nothrow_default_constructible<_Hp>::value) {}
+
+    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,
+              class = typename enable_if<is_constructible<_Hp, _Tp>::value>::type>
+        _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
+        explicit __tuple_leaf(_Tp&& __t) _NOEXCEPT_((is_nothrow_constructible<_Hp, _Tp>::value))
+            : _Hp(_VSTD::forward<_Tp>(__t)) {}
+
+    template <class _Tp, class _Alloc>
+        _LIBCPP_INLINE_VISIBILITY
+        explicit __tuple_leaf(integral_constant<int, 0>, const _Alloc&, _Tp&& __t)
+            : _Hp(_VSTD::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, _VSTD::forward<_Tp>(__t)) {}
+
+    template <class _Tp, class _Alloc>
+        _LIBCPP_INLINE_VISIBILITY
+        explicit __tuple_leaf(integral_constant<int, 2>, const _Alloc& __a, _Tp&& __t)
+            : _Hp(_VSTD::forward<_Tp>(__t), __a) {}
+
+    template <class _Tp>
+        _LIBCPP_INLINE_VISIBILITY
+        __tuple_leaf&
+        operator=(_Tp&& __t) _NOEXCEPT_((is_nothrow_assignable<_Hp&, _Tp>::value))
+        {
+            _Hp::operator=(_VSTD::forward<_Tp>(__t));
+            return *this;
+        }
+
+    _LIBCPP_INLINE_VISIBILITY
+    int
+    swap(__tuple_leaf& __t) _NOEXCEPT_(__is_nothrow_swappable<__tuple_leaf>::value)
+    {
+        _VSTD::swap(*this, __t);
+        return 0;
+    }
+
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11       _Hp& get()       _NOEXCEPT {return static_cast<_Hp&>(*this);}
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11 const _Hp& get() const _NOEXCEPT {return static_cast<const _Hp&>(*this);}
+};
+
+template <class ..._Tp>
+_LIBCPP_INLINE_VISIBILITY
+void __swallow(_Tp&&...) _NOEXCEPT {}
+
+template <bool ...> struct __all;
+
+template <>
+struct __all<>
+{
+    static const bool value = true;
+};
+
+template <bool _B0, bool ... _Bp>
+struct __all<_B0, _Bp...>
+{
+    static const bool value = _B0 && __all<_Bp...>::value;
+};
+
+// __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>...
+{
+    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_CONSTEXPR __tuple_impl()
+        _NOEXCEPT_(__all<is_nothrow_default_constructible<_Tp>::value...>::value) {}
+
+    template <size_t ..._Uf, class ..._Tf,
+              size_t ..._Ul, class ..._Tl, class ..._Up>
+        _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
+        explicit
+        __tuple_impl(__tuple_indices<_Uf...>, __tuple_types<_Tf...>,
+                     __tuple_indices<_Ul...>, __tuple_types<_Tl...>,
+                     _Up&&... __u)
+                     _NOEXCEPT_((__all<is_nothrow_constructible<_Tf, _Up>::value...>::value &&
+                                 __all<is_nothrow_default_constructible<_Tl>::value...>::value)) :
+            __tuple_leaf<_Uf, _Tf>(_VSTD::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,
+            _VSTD::forward<_Up>(__u))...,
+            __tuple_leaf<_Ul, _Tl>(__uses_alloc_ctor<_Tl, _Alloc>(), __a)...
+            {}
+
+    template <class _Tuple,
+              class = typename enable_if
+                      <
+                         __tuple_constructible<_Tuple, tuple<_Tp...> >::value
+                      >::type
+             >
+        _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
+        __tuple_impl(_Tuple&& __t) _NOEXCEPT_((__all<is_nothrow_constructible<_Tp, typename tuple_element<_Indx,
+                                       typename __make_tuple_types<_Tuple>::type>::type>::value...>::value))
+            : __tuple_leaf<_Indx, _Tp>(_VSTD::forward<typename tuple_element<_Indx,
+                                       typename __make_tuple_types<_Tuple>::type>::type>(_VSTD::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,
+                                       _VSTD::forward<typename tuple_element<_Indx,
+                                       typename __make_tuple_types<_Tuple>::type>::type>(_VSTD::get<_Indx>(__t)))...
+            {}
+
+    template <class _Tuple>
+        _LIBCPP_INLINE_VISIBILITY
+        typename enable_if
+        <
+            __tuple_assignable<_Tuple, tuple<_Tp...> >::value,
+            __tuple_impl&
+        >::type
+        operator=(_Tuple&& __t) _NOEXCEPT_((__all<is_nothrow_assignable<_Tp&, typename tuple_element<_Indx,
+                                       typename __make_tuple_types<_Tuple>::type>::type>::value...>::value))
+        {
+            __swallow(__tuple_leaf<_Indx, _Tp>::operator=(_VSTD::forward<typename tuple_element<_Indx,
+                                       typename __make_tuple_types<_Tuple>::type>::type>(_VSTD::get<_Indx>(__t)))...);
+            return *this;
+        }
+
+    __tuple_impl(const __tuple_impl&) = default;
+    __tuple_impl(__tuple_impl&&) = default;
+
+    _LIBCPP_INLINE_VISIBILITY
+    __tuple_impl&
+    operator=(const __tuple_impl& __t) _NOEXCEPT_((__all<is_nothrow_copy_assignable<_Tp>::value...>::value))
+    {
+        __swallow(__tuple_leaf<_Indx, _Tp>::operator=(static_cast<const __tuple_leaf<_Indx, _Tp>&>(__t).get())...);
+        return *this;
+    }
+
+    _LIBCPP_INLINE_VISIBILITY
+    __tuple_impl&
+    operator=(__tuple_impl&& __t) _NOEXCEPT_((__all<is_nothrow_move_assignable<_Tp>::value...>::value))
+    {
+        __swallow(__tuple_leaf<_Indx, _Tp>::operator=(_VSTD::forward<_Tp>(static_cast<__tuple_leaf<_Indx, _Tp>&>(__t).get()))...);
+        return *this;
+    }
+
+    _LIBCPP_INLINE_VISIBILITY
+    void swap(__tuple_impl& __t)
+        _NOEXCEPT_(__all<__is_nothrow_swappable<_Tp>::value...>::value)
+    {
+        __swallow(__tuple_leaf<_Indx, _Tp>::swap(static_cast<__tuple_leaf<_Indx, _Tp>&>(__t))...);
+    }
+};
+
+template <class ..._Tp>
+class _LIBCPP_TYPE_VIS_ONLY tuple
+{
+    typedef __tuple_impl<typename __make_tuple_indices<sizeof...(_Tp)>::type, _Tp...> base;
+
+    base base_;
+
+    template <size_t _Jp, class ..._Up> friend _LIBCPP_CONSTEXPR_AFTER_CXX11
+        typename tuple_element<_Jp, tuple<_Up...> >::type& get(tuple<_Up...>&) _NOEXCEPT;
+    template <size_t _Jp, class ..._Up> friend _LIBCPP_CONSTEXPR_AFTER_CXX11
+        const typename tuple_element<_Jp, tuple<_Up...> >::type& get(const tuple<_Up...>&) _NOEXCEPT;
+    template <size_t _Jp, class ..._Up> friend _LIBCPP_CONSTEXPR_AFTER_CXX11
+        typename tuple_element<_Jp, tuple<_Up...> >::type&& get(tuple<_Up...>&&) _NOEXCEPT;
+public:
+
+    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_CONSTEXPR tuple()
+        _NOEXCEPT_(__all<is_nothrow_default_constructible<_Tp>::value...>::value) {}
+
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
+    explicit tuple(const _Tp& ... __t) _NOEXCEPT_((__all<is_nothrow_copy_constructible<_Tp>::value...>::value)) 
+        : 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,
+              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,
+                         bool
+                      >::type = false
+             >
+        _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
+        tuple(_Up&&... __u)
+            _NOEXCEPT_((
+                is_nothrow_constructible<
+                    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,
+                    _Up...
+                >::value
+            ))
+            : 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(),
+                    _VSTD::forward<_Up>(__u)...) {}
+
+    template <class ..._Up,
+              typename enable_if
+                      <
+                         sizeof...(_Up) <= sizeof...(_Tp) &&
+                         __tuple_constructible
+                         <
+                            tuple<_Up...>,
+                            typename __make_tuple_types<tuple,
+                                     sizeof...(_Up) < sizeof...(_Tp) ?
+                                        sizeof...(_Up) :
+                                        sizeof...(_Tp)>::type
+                         >::value &&
+                         !__tuple_convertible
+                         <
+                            tuple<_Up...>,
+                            typename __make_tuple_types<tuple,
+                                     sizeof...(_Up) < sizeof...(_Tp) ?
+                                        sizeof...(_Up) :
+                                        sizeof...(_Tp)>::type
+                         >::value,
+                         bool
+                      >::type =false
+             >
+        _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
+        explicit
+        tuple(_Up&&... __u)
+            _NOEXCEPT_((
+                is_nothrow_constructible<
+                    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,
+                    _Up...
+                >::value
+            ))
+            : 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(),
+                    _VSTD::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(),
+                    _VSTD::forward<_Up>(__u)...) {}
+
+    template <class _Tuple,
+              typename enable_if
+                      <
+                         __tuple_convertible<_Tuple, tuple>::value,
+                         bool
+                      >::type = false
+             >
+        _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
+        tuple(_Tuple&& __t) _NOEXCEPT_((is_nothrow_constructible<base, _Tuple>::value))
+            : base_(_VSTD::forward<_Tuple>(__t)) {}
+
+    template <class _Tuple,
+              typename enable_if
+                      <
+                         __tuple_constructible<_Tuple, tuple>::value &&
+                         !__tuple_convertible<_Tuple, tuple>::value,
+                         bool
+                      >::type = false
+             >
+        _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
+        explicit
+        tuple(_Tuple&& __t) _NOEXCEPT_((is_nothrow_constructible<base, _Tuple>::value))
+            : base_(_VSTD::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, _VSTD::forward<_Tuple>(__t)) {}
+
+    template <class _Tuple,
+              class = typename enable_if
+                      <
+                         __tuple_assignable<_Tuple, tuple>::value
+                      >::type
+             >
+        _LIBCPP_INLINE_VISIBILITY
+        tuple&
+        operator=(_Tuple&& __t) _NOEXCEPT_((is_nothrow_assignable<base&, _Tuple>::value))
+        {
+            base_.operator=(_VSTD::forward<_Tuple>(__t));
+            return *this;
+        }
+
+    _LIBCPP_INLINE_VISIBILITY
+    void swap(tuple& __t) _NOEXCEPT_(__all<__is_nothrow_swappable<_Tp>::value...>::value)
+        {base_.swap(__t.base_);}
+};
+
+template <>
+class _LIBCPP_TYPE_VIS_ONLY tuple<>
+{
+public:
+    _LIBCPP_INLINE_VISIBILITY
+    _LIBCPP_CONSTEXPR tuple() _NOEXCEPT {}
+    template <class _Alloc>
+    _LIBCPP_INLINE_VISIBILITY
+        tuple(allocator_arg_t, const _Alloc&) _NOEXCEPT {}
+    template <class _Alloc>
+    _LIBCPP_INLINE_VISIBILITY
+        tuple(allocator_arg_t, const _Alloc&, const tuple&) _NOEXCEPT {}
+    template <class _Up>
+    _LIBCPP_INLINE_VISIBILITY
+        tuple(array<_Up, 0>) _NOEXCEPT {}
+    template <class _Alloc, class _Up>
+    _LIBCPP_INLINE_VISIBILITY
+        tuple(allocator_arg_t, const _Alloc&, array<_Up, 0>) _NOEXCEPT {}
+    _LIBCPP_INLINE_VISIBILITY
+    void swap(tuple&) _NOEXCEPT {}
+};
+
+template <class ..._Tp>
+inline _LIBCPP_INLINE_VISIBILITY
+typename enable_if
+<
+    __all<__is_swappable<_Tp>::value...>::value,
+    void
+>::type
+swap(tuple<_Tp...>& __t, tuple<_Tp...>& __u)
+                 _NOEXCEPT_(__all<__is_nothrow_swappable<_Tp>::value...>::value)
+    {__t.swap(__u);}
+
+// get
+
+template <size_t _Ip, class ..._Tp>
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
+typename tuple_element<_Ip, tuple<_Tp...> >::type&
+get(tuple<_Tp...>& __t) _NOEXCEPT
+{
+    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 _LIBCPP_CONSTEXPR_AFTER_CXX11
+const typename tuple_element<_Ip, tuple<_Tp...> >::type&
+get(const tuple<_Tp...>& __t) _NOEXCEPT
+{
+    typedef typename tuple_element<_Ip, tuple<_Tp...> >::type type;
+    return static_cast<const __tuple_leaf<_Ip, type>&>(__t.base_).get();
+}
+
+template <size_t _Ip, class ..._Tp>
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
+typename tuple_element<_Ip, tuple<_Tp...> >::type&&
+get(tuple<_Tp...>&& __t) _NOEXCEPT
+{
+    typedef typename tuple_element<_Ip, tuple<_Tp...> >::type type;
+    return static_cast<type&&>(
+             static_cast<__tuple_leaf<_Ip, type>&&>(__t.base_).get());
+}
+
+#if _LIBCPP_STD_VER > 11
+// get by type
+template <typename _T1, size_t _Idx, typename... _Args>
+struct __find_exactly_one_t_helper;
+
+// -- find exactly one
+template <typename _T1, size_t _Idx, typename... _Args>
+struct __find_exactly_one_t_checker {
+    static constexpr size_t value = _Idx;
+//  Check the rest of the list to make sure there's only one
+    static_assert ( __find_exactly_one_t_helper<_T1, 0, _Args...>::value == -1, "type can only occur once in type list" );
+    };
+
+
+template <typename _T1, size_t _Idx>
+struct __find_exactly_one_t_helper <_T1, _Idx> {
+    static constexpr size_t value = -1;
+    };
+
+template <typename _T1, size_t _Idx, typename _Head, typename... _Args>
+struct __find_exactly_one_t_helper <_T1, _Idx, _Head, _Args...> {
+    static constexpr size_t value =
+        std::conditional<
+            std::is_same<_T1, _Head>::value,
+            __find_exactly_one_t_checker<_T1, _Idx,   _Args...>,
+            __find_exactly_one_t_helper <_T1, _Idx+1, _Args...>
+        >::type::value;
+    };
+
+template <typename _T1, typename... _Args>
+struct __find_exactly_one_t {
+    static constexpr size_t value = __find_exactly_one_t_helper<_T1, 0, _Args...>::value;
+    static_assert ( value != -1, "type not found in type list" );
+    };
+
+template <class _T1, class... _Args>
+inline _LIBCPP_INLINE_VISIBILITY
+constexpr _T1& get(tuple<_Args...>& __tup) noexcept
+{
+    return _VSTD::get<__find_exactly_one_t<_T1, _Args...>::value>(__tup);
+}
+
+template <class _T1, class... _Args>
+inline _LIBCPP_INLINE_VISIBILITY
+constexpr _T1 const& get(tuple<_Args...> const& __tup) noexcept
+{
+    return _VSTD::get<__find_exactly_one_t<_T1, _Args...>::value>(__tup);
+}
+
+template <class _T1, class... _Args>
+inline _LIBCPP_INLINE_VISIBILITY
+constexpr _T1&& get(tuple<_Args...>&& __tup) noexcept
+{
+    return _VSTD::get<__find_exactly_one_t<_T1, _Args...>::value>(_VSTD::move(__tup));
+}
+
+#endif
+
+// tie
+
+template <class ..._Tp>
+inline _LIBCPP_INLINE_VISIBILITY
+tuple<_Tp&...>
+tie(_Tp&... __t) _NOEXCEPT
+{
+    return tuple<_Tp&...>(__t...);
+}
+
+template <class _Up>
+struct __ignore_t
+{
+    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 _LIBCPP_TYPE_VIS_ONLY 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 _LIBCPP_CONSTEXPR_AFTER_CXX11
+tuple<typename __make_tuple_return<_Tp>::type...>
+make_tuple(_Tp&&... __t)
+{
+    return tuple<typename __make_tuple_return<_Tp>::type...>(_VSTD::forward<_Tp>(__t)...);
+}
+
+template <class... _Tp>
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
+tuple<_Tp&&...>
+forward_as_tuple(_Tp&&... __t) _NOEXCEPT
+{
+    return tuple<_Tp&&...>(_VSTD::forward<_Tp>(__t)...);
+}
+
+template <size_t _Ip>
+struct __tuple_equal
+{
+    template <class _Tp, class _Up>
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
+    bool operator()(const _Tp& __x, const _Up& __y)
+    {
+        return __tuple_equal<_Ip - 1>()(__x, __y) && get<_Ip-1>(__x) == get<_Ip-1>(__y);
+    }
+};
+
+template <>
+struct __tuple_equal<0>
+{
+    template <class _Tp, class _Up>
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
+    bool operator()(const _Tp&, const _Up&)
+    {
+        return true;
+    }
+};
+
+template <class ..._Tp, class ..._Up>
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
+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 _LIBCPP_CONSTEXPR_AFTER_CXX11
+bool
+operator!=(const tuple<_Tp...>& __x, const tuple<_Up...>& __y)
+{
+    return !(__x == __y);
+}
+
+template <size_t _Ip>
+struct __tuple_less
+{
+    template <class _Tp, class _Up>
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
+    bool operator()(const _Tp& __x, const _Up& __y)
+    {
+        return __tuple_less<_Ip-1>()(__x, __y) ||
+             (!__tuple_less<_Ip-1>()(__y, __x) && get<_Ip-1>(__x) < get<_Ip-1>(__y));
+    }
+};
+
+template <>
+struct __tuple_less<0>
+{
+    template <class _Tp, class _Up>
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
+    bool operator()(const _Tp&, const _Up&)
+    {
+        return false;
+    }
+};
+
+template <class ..._Tp, class ..._Up>
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
+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 _LIBCPP_CONSTEXPR_AFTER_CXX11
+bool
+operator>(const tuple<_Tp...>& __x, const tuple<_Up...>& __y)
+{
+    return __y < __x;
+}
+
+template <class ..._Tp, class ..._Up>
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
+bool
+operator>=(const tuple<_Tp...>& __x, const tuple<_Up...>& __y)
+{
+    return !(__x < __y);
+}
+
+template <class ..._Tp, class ..._Up>
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
+bool
+operator<=(const tuple<_Tp...>& __x, const tuple<_Up...>& __y)
+{
+    return !(__y < __x);
+}
+
+// tuple_cat
+
+template <class _Tp, class _Up> struct __tuple_cat_type;
+
+template <class ..._Ttypes, class ..._Utypes>
+struct __tuple_cat_type<tuple<_Ttypes...>, __tuple_types<_Utypes...> >
+{
+    typedef tuple<_Ttypes..., _Utypes...> type;
+};
+
+template <class _ResultTuple, bool _Is_Tuple0TupleLike, class ..._Tuples>
+struct __tuple_cat_return_1
+{
+};
+
+template <class ..._Types, class _Tuple0>
+struct __tuple_cat_return_1<tuple<_Types...>, true, _Tuple0>
+{
+    typedef typename __tuple_cat_type<tuple<_Types...>,
+            typename __make_tuple_types<typename remove_reference<_Tuple0>::type>::type>::type
+                                                                           type;
+};
+
+template <class ..._Types, class _Tuple0, class _Tuple1, class ..._Tuples>
+struct __tuple_cat_return_1<tuple<_Types...>, true, _Tuple0, _Tuple1, _Tuples...>
+    : public __tuple_cat_return_1<
+                 typename __tuple_cat_type<
+                     tuple<_Types...>,
+                     typename __make_tuple_types<typename remove_reference<_Tuple0>::type>::type
+                 >::type,
+                 __tuple_like<typename remove_reference<_Tuple1>::type>::value,
+                 _Tuple1, _Tuples...>
+{
+};
+
+template <class ..._Tuples> struct __tuple_cat_return;
+
+template <class _Tuple0, class ..._Tuples>
+struct __tuple_cat_return<_Tuple0, _Tuples...>
+    : public __tuple_cat_return_1<tuple<>,
+         __tuple_like<typename remove_reference<_Tuple0>::type>::value, _Tuple0,
+                                                                     _Tuples...>
+{
+};
+
+template <>
+struct __tuple_cat_return<>
+{
+    typedef tuple<> type;
+};
+
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
+tuple<>
+tuple_cat()
+{
+    return tuple<>();
+}
+
+template <class _Rp, class _Indices, class _Tuple0, class ..._Tuples>
+struct __tuple_cat_return_ref_imp;
+
+template <class ..._Types, size_t ..._I0, class _Tuple0>
+struct __tuple_cat_return_ref_imp<tuple<_Types...>, __tuple_indices<_I0...>, _Tuple0>
+{
+    typedef typename remove_reference<_Tuple0>::type _T0;
+    typedef tuple<_Types..., typename __apply_cv<_Tuple0,
+                          typename tuple_element<_I0, _T0>::type>::type&&...> type;
+};
+
+template <class ..._Types, size_t ..._I0, class _Tuple0, class _Tuple1, class ..._Tuples>
+struct __tuple_cat_return_ref_imp<tuple<_Types...>, __tuple_indices<_I0...>,
+                                  _Tuple0, _Tuple1, _Tuples...>
+    : public __tuple_cat_return_ref_imp<
+         tuple<_Types..., typename __apply_cv<_Tuple0,
+               typename tuple_element<_I0,
+                  typename remove_reference<_Tuple0>::type>::type>::type&&...>,
+         typename __make_tuple_indices<tuple_size<typename
+                                 remove_reference<_Tuple1>::type>::value>::type,
+         _Tuple1, _Tuples...>
+{
+};
+
+template <class _Tuple0, class ..._Tuples>
+struct __tuple_cat_return_ref
+    : public __tuple_cat_return_ref_imp<tuple<>,
+               typename __make_tuple_indices<
+                        tuple_size<typename remove_reference<_Tuple0>::type>::value
+               >::type, _Tuple0, _Tuples...>
+{
+};
+
+template <class _Types, class _I0, class _J0>
+struct __tuple_cat;
+
+template <class ..._Types, size_t ..._I0, size_t ..._J0>
+struct __tuple_cat<tuple<_Types...>, __tuple_indices<_I0...>, __tuple_indices<_J0...> >
+{
+    template <class _Tuple0>
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
+    typename __tuple_cat_return_ref<tuple<_Types...>&&, _Tuple0&&>::type
+    operator()(tuple<_Types...> __t, _Tuple0&& __t0)
+    {
+        return forward_as_tuple(_VSTD::forward<_Types>(get<_I0>(__t))...,
+                                      get<_J0>(_VSTD::forward<_Tuple0>(__t0))...);
+    }
+
+    template <class _Tuple0, class _Tuple1, class ..._Tuples>
+    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
+    typename __tuple_cat_return_ref<tuple<_Types...>&&, _Tuple0&&, _Tuple1&&, _Tuples&&...>::type
+    operator()(tuple<_Types...> __t, _Tuple0&& __t0, _Tuple1&& __t1, _Tuples&& ...__tpls)
+    {
+        typedef typename remove_reference<_Tuple0>::type _T0;
+        typedef typename remove_reference<_Tuple1>::type _T1;
+        return __tuple_cat<
+           tuple<_Types..., typename __apply_cv<_Tuple0, typename tuple_element<_J0, _T0>::type>::type&&...>,
+           typename __make_tuple_indices<sizeof ...(_Types) + tuple_size<_T0>::value>::type,
+           typename __make_tuple_indices<tuple_size<_T1>::value>::type>()
+                           (forward_as_tuple(
+                              _VSTD::forward<_Types>(get<_I0>(__t))...,
+                              get<_J0>(_VSTD::forward<_Tuple0>(__t0))...
+                            ),
+                            _VSTD::forward<_Tuple1>(__t1),
+                            _VSTD::forward<_Tuples>(__tpls)...);
+    }
+};
+
+template <class _Tuple0, class... _Tuples>
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
+typename __tuple_cat_return<_Tuple0, _Tuples...>::type
+tuple_cat(_Tuple0&& __t0, _Tuples&&... __tpls)
+{
+    typedef typename remove_reference<_Tuple0>::type _T0;
+    return __tuple_cat<tuple<>, __tuple_indices<>,
+                  typename __make_tuple_indices<tuple_size<_T0>::value>::type>()
+                  (tuple<>(), _VSTD::forward<_Tuple0>(__t0),
+                                            _VSTD::forward<_Tuples>(__tpls)...);
+}
+
+template <class ..._Tp, class _Alloc>
+struct _LIBCPP_TYPE_VIS_ONLY 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(_VSTD::forward<_Args1>(get<_I1>( __first_args))...),
+      second(_VSTD::forward<_Args2>(get<_I2>(__second_args))...)
+{
+}
+
+#endif  // _LIBCPP_HAS_NO_VARIADICS
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif  // _LIBCPP_TUPLE