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 // -*- C++ -*-
 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef _LIBCPP___MEMORY_SHARED_PTR_H
 #define _LIBCPP___MEMORY_SHARED_PTR_H
 
 #include <__compare/compare_three_way.h>
 #include <__compare/ordering.h>
 #include <__config>
 #include <__cstddef/nullptr_t.h>
 #include <__cstddef/ptrdiff_t.h>
 #include <__exception/exception.h>
 #include <__functional/binary_function.h>
 #include <__functional/operations.h>
 #include <__functional/reference_wrapper.h>
 #include <__fwd/ostream.h>
 #include <__iterator/access.h>
 #include <__memory/addressof.h>
 #include <__memory/allocation_guard.h>
 #include <__memory/allocator.h>
 #include <__memory/allocator_destructor.h>
 #include <__memory/allocator_traits.h>
 #include <__memory/auto_ptr.h>
 #include <__memory/compressed_pair.h>
 #include <__memory/construct_at.h>
 #include <__memory/pointer_traits.h>
 #include <__memory/shared_count.h>
 #include <__memory/uninitialized_algorithms.h>
 #include <__memory/unique_ptr.h>
 #include <__type_traits/add_lvalue_reference.h>
 #include <__type_traits/conditional.h>
 #include <__type_traits/conjunction.h>
 #include <__type_traits/disjunction.h>
 #include <__type_traits/enable_if.h>
 #include <__type_traits/integral_constant.h>
 #include <__type_traits/is_array.h>
 #include <__type_traits/is_bounded_array.h>
 #include <__type_traits/is_constructible.h>
 #include <__type_traits/is_convertible.h>
 #include <__type_traits/is_function.h>
 #include <__type_traits/is_reference.h>
 #include <__type_traits/is_same.h>
 #include <__type_traits/is_unbounded_array.h>
 #include <__type_traits/nat.h>
 #include <__type_traits/negation.h>
 #include <__type_traits/remove_cv.h>
 #include <__type_traits/remove_extent.h>
 #include <__type_traits/remove_reference.h>
 #include <__utility/declval.h>
 #include <__utility/forward.h>
 #include <__utility/move.h>
 #include <__utility/swap.h>
 #include <__verbose_abort>
 #include <typeinfo>
 #if _LIBCPP_HAS_ATOMIC_HEADER
 #  include <__atomic/memory_order.h>
 #endif
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
 
 _LIBCPP_PUSH_MACROS
 #include <__undef_macros>
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 class _LIBCPP_EXPORTED_FROM_ABI bad_weak_ptr : public std::exception {
 public:
   _LIBCPP_HIDE_FROM_ABI bad_weak_ptr() _NOEXCEPT                               = default;
   _LIBCPP_HIDE_FROM_ABI bad_weak_ptr(const bad_weak_ptr&) _NOEXCEPT            = default;
   _LIBCPP_HIDE_FROM_ABI bad_weak_ptr& operator=(const bad_weak_ptr&) _NOEXCEPT = default;
   ~bad_weak_ptr() _NOEXCEPT override;
   const char* what() const _NOEXCEPT override;
 };
 
 [[__noreturn__]] inline _LIBCPP_HIDE_FROM_ABI void __throw_bad_weak_ptr() {
 #if _LIBCPP_HAS_EXCEPTIONS
   throw bad_weak_ptr();
 #else
   _LIBCPP_VERBOSE_ABORT("bad_weak_ptr was thrown in -fno-exceptions mode");
 #endif
 }
 
 template <class _Tp>
 class _LIBCPP_TEMPLATE_VIS weak_ptr;
 
 template <class _Tp, class _Dp, class _Alloc>
 class __shared_ptr_pointer : public __shared_weak_count {
   _LIBCPP_COMPRESSED_TRIPLE(_Tp, __ptr_, _Dp, __deleter_, _Alloc, __alloc_);
 
 public:
   _LIBCPP_HIDE_FROM_ABI __shared_ptr_pointer(_Tp __p, _Dp __d, _Alloc __a)
       : __ptr_(__p), __deleter_(std::move(__d)), __alloc_(std::move(__a)) {}
 
 #if _LIBCPP_HAS_RTTI
   _LIBCPP_HIDE_FROM_ABI_VIRTUAL const void* __get_deleter(const type_info&) const _NOEXCEPT override;
 #endif
 
 private:
   _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared() _NOEXCEPT override;
   _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared_weak() _NOEXCEPT override;
 };
 
 #if _LIBCPP_HAS_RTTI
 
 template <class _Tp, class _Dp, class _Alloc>
 const void* __shared_ptr_pointer<_Tp, _Dp, _Alloc>::__get_deleter(const type_info& __t) const _NOEXCEPT {
   return __t == typeid(_Dp) ? std::addressof(__deleter_) : nullptr;
 }
 
 #endif // _LIBCPP_HAS_RTTI
 
 template <class _Tp, class _Dp, class _Alloc>
 void __shared_ptr_pointer<_Tp, _Dp, _Alloc>::__on_zero_shared() _NOEXCEPT {
   __deleter_(__ptr_);
   __deleter_.~_Dp();
 }
 
 template <class _Tp, class _Dp, class _Alloc>
 void __shared_ptr_pointer<_Tp, _Dp, _Alloc>::__on_zero_shared_weak() _NOEXCEPT {
   typedef typename __allocator_traits_rebind<_Alloc, __shared_ptr_pointer>::type _Al;
   typedef allocator_traits<_Al> _ATraits;
   typedef pointer_traits<typename _ATraits::pointer> _PTraits;
 
   _Al __a(__alloc_);
   __alloc_.~_Alloc();
   __a.deallocate(_PTraits::pointer_to(*this), 1);
 }
 
 // This tag is used to instantiate an allocator type. The various shared_ptr control blocks
 // detect that the allocator has been instantiated for this type and perform alternative
 // initialization/destruction based on that.
 struct __for_overwrite_tag {};
 
 template <class _Tp, class _Alloc>
 struct __shared_ptr_emplace : __shared_weak_count {
   using __value_type _LIBCPP_NODEBUG = __remove_cv_t<_Tp>;
 
   template <class... _Args,
             class _Allocator                                                                         = _Alloc,
             __enable_if_t<is_same<typename _Allocator::value_type, __for_overwrite_tag>::value, int> = 0>
   _LIBCPP_HIDE_FROM_ABI explicit __shared_ptr_emplace(_Alloc __a, _Args&&...) : __storage_(std::move(__a)) {
     static_assert(
         sizeof...(_Args) == 0, "No argument should be provided to the control block when using _for_overwrite");
     ::new (static_cast<void*>(__get_elem())) __value_type;
   }
 
   template <class... _Args,
             class _Allocator                                                                          = _Alloc,
             __enable_if_t<!is_same<typename _Allocator::value_type, __for_overwrite_tag>::value, int> = 0>
   _LIBCPP_HIDE_FROM_ABI explicit __shared_ptr_emplace(_Alloc __a, _Args&&... __args) : __storage_(std::move(__a)) {
     using _TpAlloc = typename __allocator_traits_rebind<_Alloc, __value_type>::type;
     _TpAlloc __tmp(*__get_alloc());
     allocator_traits<_TpAlloc>::construct(__tmp, __get_elem(), std::forward<_Args>(__args)...);
   }
 
   _LIBCPP_HIDE_FROM_ABI _Alloc* __get_alloc() _NOEXCEPT { return __storage_.__get_alloc(); }
 
   _LIBCPP_HIDE_FROM_ABI __value_type* __get_elem() _NOEXCEPT { return __storage_.__get_elem(); }
 
 private:
   template <class _Allocator                                                                         = _Alloc,
             __enable_if_t<is_same<typename _Allocator::value_type, __for_overwrite_tag>::value, int> = 0>
   _LIBCPP_HIDE_FROM_ABI void __on_zero_shared_impl() _NOEXCEPT {
     __get_elem()->~__value_type();
   }
 
   template <class _Allocator                                                                          = _Alloc,
             __enable_if_t<!is_same<typename _Allocator::value_type, __for_overwrite_tag>::value, int> = 0>
   _LIBCPP_HIDE_FROM_ABI void __on_zero_shared_impl() _NOEXCEPT {
     using _TpAlloc = typename __allocator_traits_rebind<_Allocator, __remove_cv_t<_Tp> >::type;
     _TpAlloc __tmp(*__get_alloc());
     allocator_traits<_TpAlloc>::destroy(__tmp, __get_elem());
   }
 
   _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared() _NOEXCEPT override { __on_zero_shared_impl(); }
 
   _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared_weak() _NOEXCEPT override {
     using _ControlBlockAlloc   = typename __allocator_traits_rebind<_Alloc, __shared_ptr_emplace>::type;
     using _ControlBlockPointer = typename allocator_traits<_ControlBlockAlloc>::pointer;
     _ControlBlockAlloc __tmp(*__get_alloc());
     __storage_.~_Storage();
     allocator_traits<_ControlBlockAlloc>::deallocate(__tmp, pointer_traits<_ControlBlockPointer>::pointer_to(*this), 1);
   }
 
   // TODO: It should be possible to refactor this to remove `_Storage` entirely.
   // This class implements the control block for non-array shared pointers created
   // through `std::allocate_shared` and `std::make_shared`.
   struct _Storage {
     struct _Data {
       _LIBCPP_COMPRESSED_PAIR(_Alloc, __alloc_, __value_type, __elem_);
     };
 
     _ALIGNAS_TYPE(_Data) char __buffer_[sizeof(_Data)];
 
     _LIBCPP_HIDE_FROM_ABI explicit _Storage(_Alloc&& __a) { ::new ((void*)__get_alloc()) _Alloc(std::move(__a)); }
     _LIBCPP_HIDE_FROM_ABI ~_Storage() { __get_alloc()->~_Alloc(); }
 
     _LIBCPP_HIDE_FROM_ABI _Alloc* __get_alloc() _NOEXCEPT {
       return std::addressof(reinterpret_cast<_Data*>(__buffer_)->__alloc_);
     }
 
     _LIBCPP_HIDE_FROM_ABI _LIBCPP_NO_CFI __value_type* __get_elem() _NOEXCEPT {
       return std::addressof(reinterpret_cast<_Data*>(__buffer_)->__elem_);
     }
   };
 
   _Storage __storage_;
 };
 
 struct __shared_ptr_dummy_rebind_allocator_type;
 template <>
 class _LIBCPP_TEMPLATE_VIS allocator<__shared_ptr_dummy_rebind_allocator_type> {
 public:
   template <class _Other>
   struct rebind {
     typedef allocator<_Other> other;
   };
 };
 
 template <class _Tp>
 class _LIBCPP_TEMPLATE_VIS enable_shared_from_this;
 
 // http://eel.is/c++draft/util.sharedptr#util.smartptr.shared.general-6
 // A pointer type Y* is said to be compatible with a pointer type T*
 // when either Y* is convertible to T* or Y is U[N] and T is cv U[].
 #if _LIBCPP_STD_VER >= 17
 template <class _Yp, class _Tp>
 struct __bounded_convertible_to_unbounded : false_type {};
 
 template <class _Up, std::size_t _Np, class _Tp>
 struct __bounded_convertible_to_unbounded<_Up[_Np], _Tp> : is_same<__remove_cv_t<_Tp>, _Up[]> {};
 
 template <class _Yp, class _Tp>
 struct __compatible_with : _Or< is_convertible<_Yp*, _Tp*>, __bounded_convertible_to_unbounded<_Yp, _Tp> > {};
 #else
 template <class _Yp, class _Tp>
 struct __compatible_with : is_convertible<_Yp*, _Tp*> {};
 #endif // _LIBCPP_STD_VER >= 17
 
 // Constructors that take raw pointers have a different set of "compatible" constraints
 // http://eel.is/c++draft/util.sharedptr#util.smartptr.shared.const-9.1
 // - If T is an array type, then either T is U[N] and Y(*)[N] is convertible to T*,
 //   or T is U[] and Y(*)[] is convertible to T*.
 // - If T is not an array type, then Y* is convertible to T*.
 #if _LIBCPP_STD_VER >= 17
 template <class _Yp, class _Tp, class = void>
 struct __raw_pointer_compatible_with : _And< _Not<is_array<_Tp>>, is_convertible<_Yp*, _Tp*> > {};
 
 template <class _Yp, class _Up, std::size_t _Np>
 struct __raw_pointer_compatible_with<_Yp, _Up[_Np], __enable_if_t< is_convertible<_Yp (*)[_Np], _Up (*)[_Np]>::value> >
     : true_type {};
 
 template <class _Yp, class _Up>
 struct __raw_pointer_compatible_with<_Yp, _Up[], __enable_if_t< is_convertible<_Yp (*)[], _Up (*)[]>::value> >
     : true_type {};
 
 #else
 template <class _Yp, class _Tp>
 struct __raw_pointer_compatible_with : is_convertible<_Yp*, _Tp*> {};
 #endif // _LIBCPP_STD_VER >= 17
 
 template <class _Ptr, class = void>
 struct __is_deletable : false_type {};
 template <class _Ptr>
 struct __is_deletable<_Ptr, decltype(delete std::declval<_Ptr>())> : true_type {};
 
 template <class _Ptr, class = void>
 struct __is_array_deletable : false_type {};
 template <class _Ptr>
 struct __is_array_deletable<_Ptr, decltype(delete[] std::declval<_Ptr>())> : true_type {};
 
 template <class _Dp, class _Pt, class = decltype(std::declval<_Dp>()(std::declval<_Pt>()))>
 true_type __well_formed_deleter_test(int);
 
 template <class, class>
 false_type __well_formed_deleter_test(...);
 
 template <class _Dp, class _Pt>
 struct __well_formed_deleter : decltype(std::__well_formed_deleter_test<_Dp, _Pt>(0)) {};
 
 template <class _Dp, class _Yp, class _Tp>
 struct __shared_ptr_deleter_ctor_reqs {
   static const bool value = __raw_pointer_compatible_with<_Yp, _Tp>::value && is_move_constructible<_Dp>::value &&
                             __well_formed_deleter<_Dp, _Yp*>::value;
 };
 
 template <class _Dp>
 using __shared_ptr_nullptr_deleter_ctor_reqs _LIBCPP_NODEBUG =
     _And<is_move_constructible<_Dp>, __well_formed_deleter<_Dp, nullptr_t> >;
 
 #if defined(_LIBCPP_ABI_ENABLE_SHARED_PTR_TRIVIAL_ABI)
 #  define _LIBCPP_SHARED_PTR_TRIVIAL_ABI __attribute__((__trivial_abi__))
 #else
 #  define _LIBCPP_SHARED_PTR_TRIVIAL_ABI
 #endif
 
 template <class _Tp>
 class _LIBCPP_SHARED_PTR_TRIVIAL_ABI _LIBCPP_TEMPLATE_VIS shared_ptr {
   struct __nullptr_sfinae_tag {};
 
 public:
 #if _LIBCPP_STD_VER >= 17
   typedef weak_ptr<_Tp> weak_type;
   typedef remove_extent_t<_Tp> element_type;
 #else
   typedef _Tp element_type;
 #endif
 
   // A shared_ptr contains only two raw pointers which point to the heap and move constructing already doesn't require
   // any bookkeeping, so it's always trivially relocatable.
   using __trivially_relocatable _LIBCPP_NODEBUG = shared_ptr;
 
 private:
   element_type* __ptr_;
   __shared_weak_count* __cntrl_;
 
 public:
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR shared_ptr() _NOEXCEPT : __ptr_(nullptr), __cntrl_(nullptr) {}
 
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR shared_ptr(nullptr_t) _NOEXCEPT : __ptr_(nullptr), __cntrl_(nullptr) {}
 
   template <class _Yp,
             __enable_if_t< _And< __raw_pointer_compatible_with<_Yp, _Tp>
   // In C++03 we get errors when trying to do SFINAE with the
   // delete operator, so we always pretend that it's deletable.
   // The same happens on GCC.
 #if !defined(_LIBCPP_CXX03_LANG) && !defined(_LIBCPP_COMPILER_GCC)
                                  ,
                                  _If<is_array<_Tp>::value, __is_array_deletable<_Yp*>, __is_deletable<_Yp*> >
 #endif
                                  >::value,
                            int> = 0>
   _LIBCPP_HIDE_FROM_ABI explicit shared_ptr(_Yp* __p) : __ptr_(__p) {
     unique_ptr<_Yp> __hold(__p);
     typedef typename __shared_ptr_default_allocator<_Yp>::type _AllocT;
     typedef __shared_ptr_pointer<_Yp*, __shared_ptr_default_delete<_Tp, _Yp>, _AllocT> _CntrlBlk;
     __cntrl_ = new _CntrlBlk(__p, __shared_ptr_default_delete<_Tp, _Yp>(), _AllocT());
     __hold.release();
     __enable_weak_this(__p, __p);
   }
 
   template <class _Yp, class _Dp, __enable_if_t<__shared_ptr_deleter_ctor_reqs<_Dp, _Yp, _Tp>::value, int> = 0>
   _LIBCPP_HIDE_FROM_ABI shared_ptr(_Yp* __p, _Dp __d) : __ptr_(__p) {
 #if _LIBCPP_HAS_EXCEPTIONS
     try {
 #endif // _LIBCPP_HAS_EXCEPTIONS
       typedef typename __shared_ptr_default_allocator<_Yp>::type _AllocT;
       typedef __shared_ptr_pointer<_Yp*, _Dp, _AllocT> _CntrlBlk;
 #ifndef _LIBCPP_CXX03_LANG
       __cntrl_ = new _CntrlBlk(__p, std::move(__d), _AllocT());
 #else
     __cntrl_ = new _CntrlBlk(__p, __d, _AllocT());
 #endif // not _LIBCPP_CXX03_LANG
       __enable_weak_this(__p, __p);
 #if _LIBCPP_HAS_EXCEPTIONS
     } catch (...) {
       __d(__p);
       throw;
     }
 #endif // _LIBCPP_HAS_EXCEPTIONS
   }
 
   template <class _Yp,
             class _Dp,
             class _Alloc,
             __enable_if_t<__shared_ptr_deleter_ctor_reqs<_Dp, _Yp, _Tp>::value, int> = 0>
   _LIBCPP_HIDE_FROM_ABI shared_ptr(_Yp* __p, _Dp __d, _Alloc __a) : __ptr_(__p) {
 #if _LIBCPP_HAS_EXCEPTIONS
     try {
 #endif // _LIBCPP_HAS_EXCEPTIONS
       typedef __shared_ptr_pointer<_Yp*, _Dp, _Alloc> _CntrlBlk;
       typedef typename __allocator_traits_rebind<_Alloc, _CntrlBlk>::type _A2;
       typedef __allocator_destructor<_A2> _D2;
       _A2 __a2(__a);
       unique_ptr<_CntrlBlk, _D2> __hold2(__a2.allocate(1), _D2(__a2, 1));
       ::new ((void*)std::addressof(*__hold2.get()))
 #ifndef _LIBCPP_CXX03_LANG
           _CntrlBlk(__p, std::move(__d), __a);
 #else
         _CntrlBlk(__p, __d, __a);
 #endif // not _LIBCPP_CXX03_LANG
       __cntrl_ = std::addressof(*__hold2.release());
       __enable_weak_this(__p, __p);
 #if _LIBCPP_HAS_EXCEPTIONS
     } catch (...) {
       __d(__p);
       throw;
     }
 #endif // _LIBCPP_HAS_EXCEPTIONS
   }
 
   template <class _Dp>
   _LIBCPP_HIDE_FROM_ABI shared_ptr(
       nullptr_t __p,
       _Dp __d,
       __enable_if_t<__shared_ptr_nullptr_deleter_ctor_reqs<_Dp>::value, __nullptr_sfinae_tag> = __nullptr_sfinae_tag())
       : __ptr_(nullptr) {
 #if _LIBCPP_HAS_EXCEPTIONS
     try {
 #endif // _LIBCPP_HAS_EXCEPTIONS
       typedef typename __shared_ptr_default_allocator<_Tp>::type _AllocT;
       typedef __shared_ptr_pointer<nullptr_t, _Dp, _AllocT> _CntrlBlk;
 #ifndef _LIBCPP_CXX03_LANG
       __cntrl_ = new _CntrlBlk(__p, std::move(__d), _AllocT());
 #else
     __cntrl_ = new _CntrlBlk(__p, __d, _AllocT());
 #endif // not _LIBCPP_CXX03_LANG
 #if _LIBCPP_HAS_EXCEPTIONS
     } catch (...) {
       __d(__p);
       throw;
     }
 #endif // _LIBCPP_HAS_EXCEPTIONS
   }
 
   template <class _Dp, class _Alloc>
   _LIBCPP_HIDE_FROM_ABI shared_ptr(
       nullptr_t __p,
       _Dp __d,
       _Alloc __a,
       __enable_if_t<__shared_ptr_nullptr_deleter_ctor_reqs<_Dp>::value, __nullptr_sfinae_tag> = __nullptr_sfinae_tag())
       : __ptr_(nullptr) {
 #if _LIBCPP_HAS_EXCEPTIONS
     try {
 #endif // _LIBCPP_HAS_EXCEPTIONS
       typedef __shared_ptr_pointer<nullptr_t, _Dp, _Alloc> _CntrlBlk;
       typedef typename __allocator_traits_rebind<_Alloc, _CntrlBlk>::type _A2;
       typedef __allocator_destructor<_A2> _D2;
       _A2 __a2(__a);
       unique_ptr<_CntrlBlk, _D2> __hold2(__a2.allocate(1), _D2(__a2, 1));
       ::new ((void*)std::addressof(*__hold2.get()))
 #ifndef _LIBCPP_CXX03_LANG
           _CntrlBlk(__p, std::move(__d), __a);
 #else
         _CntrlBlk(__p, __d, __a);
 #endif // not _LIBCPP_CXX03_LANG
       __cntrl_ = std::addressof(*__hold2.release());
 #if _LIBCPP_HAS_EXCEPTIONS
     } catch (...) {
       __d(__p);
       throw;
     }
 #endif // _LIBCPP_HAS_EXCEPTIONS
   }
 
   template <class _Yp>
   _LIBCPP_HIDE_FROM_ABI shared_ptr(const shared_ptr<_Yp>& __r, element_type* __p) _NOEXCEPT
       : __ptr_(__p),
         __cntrl_(__r.__cntrl_) {
     if (__cntrl_)
       __cntrl_->__add_shared();
   }
 
 // LWG-2996
 // We don't backport because it is an evolutionary change.
 #if _LIBCPP_STD_VER >= 20
   template <class _Yp>
   _LIBCPP_HIDE_FROM_ABI shared_ptr(shared_ptr<_Yp>&& __r, element_type* __p) noexcept
       : __ptr_(__p), __cntrl_(__r.__cntrl_) {
     __r.__ptr_   = nullptr;
     __r.__cntrl_ = nullptr;
   }
 #endif
 
   _LIBCPP_HIDE_FROM_ABI shared_ptr(const shared_ptr& __r) _NOEXCEPT : __ptr_(__r.__ptr_), __cntrl_(__r.__cntrl_) {
     if (__cntrl_)
       __cntrl_->__add_shared();
   }
 
   template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
   _LIBCPP_HIDE_FROM_ABI shared_ptr(const shared_ptr<_Yp>& __r) _NOEXCEPT : __ptr_(__r.__ptr_), __cntrl_(__r.__cntrl_) {
     if (__cntrl_)
       __cntrl_->__add_shared();
   }
 
   _LIBCPP_HIDE_FROM_ABI shared_ptr(shared_ptr&& __r) _NOEXCEPT : __ptr_(__r.__ptr_), __cntrl_(__r.__cntrl_) {
     __r.__ptr_   = nullptr;
     __r.__cntrl_ = nullptr;
   }
 
   template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
   _LIBCPP_HIDE_FROM_ABI shared_ptr(shared_ptr<_Yp>&& __r) _NOEXCEPT : __ptr_(__r.__ptr_), __cntrl_(__r.__cntrl_) {
     __r.__ptr_   = nullptr;
     __r.__cntrl_ = nullptr;
   }
 
   template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
   _LIBCPP_HIDE_FROM_ABI explicit shared_ptr(const weak_ptr<_Yp>& __r)
       : __ptr_(__r.__ptr_), __cntrl_(__r.__cntrl_ ? __r.__cntrl_->lock() : __r.__cntrl_) {
     if (__cntrl_ == nullptr)
       __throw_bad_weak_ptr();
   }
 
 #if _LIBCPP_STD_VER <= 14 || defined(_LIBCPP_ENABLE_CXX17_REMOVED_AUTO_PTR)
   template <class _Yp, __enable_if_t<is_convertible<_Yp*, element_type*>::value, int> = 0>
   _LIBCPP_HIDE_FROM_ABI shared_ptr(auto_ptr<_Yp>&& __r) : __ptr_(__r.get()) {
     typedef __shared_ptr_pointer<_Yp*, default_delete<_Yp>, allocator<__remove_cv_t<_Yp> > > _CntrlBlk;
     __cntrl_ = new _CntrlBlk(__r.get(), default_delete<_Yp>(), allocator<__remove_cv_t<_Yp> >());
     __enable_weak_this(__r.get(), __r.get());
     __r.release();
   }
 #endif
 
   template <class _Yp,
             class _Dp,
             __enable_if_t<!is_lvalue_reference<_Dp>::value && __compatible_with<_Yp, _Tp>::value &&
                               is_convertible<typename unique_ptr<_Yp, _Dp>::pointer, element_type*>::value,
                           int> = 0>
   _LIBCPP_HIDE_FROM_ABI shared_ptr(unique_ptr<_Yp, _Dp>&& __r) : __ptr_(__r.get()) {
 #if _LIBCPP_STD_VER >= 14
     if (__ptr_ == nullptr)
       __cntrl_ = nullptr;
     else
 #endif
     {
       typedef typename __shared_ptr_default_allocator<_Yp>::type _AllocT;
       typedef __shared_ptr_pointer<typename unique_ptr<_Yp, _Dp>::pointer, _Dp, _AllocT> _CntrlBlk;
       __cntrl_ = new _CntrlBlk(__r.get(), std::move(__r.get_deleter()), _AllocT());
       __enable_weak_this(__r.get(), __r.get());
     }
     __r.release();
   }
 
   template <class _Yp,
             class _Dp,
             class              = void,
             __enable_if_t<is_lvalue_reference<_Dp>::value && __compatible_with<_Yp, _Tp>::value &&
                               is_convertible<typename unique_ptr<_Yp, _Dp>::pointer, element_type*>::value,
                           int> = 0>
   _LIBCPP_HIDE_FROM_ABI shared_ptr(unique_ptr<_Yp, _Dp>&& __r) : __ptr_(__r.get()) {
 #if _LIBCPP_STD_VER >= 14
     if (__ptr_ == nullptr)
       __cntrl_ = nullptr;
     else
 #endif
     {
       typedef typename __shared_ptr_default_allocator<_Yp>::type _AllocT;
       typedef __shared_ptr_pointer<typename unique_ptr<_Yp, _Dp>::pointer,
                                    reference_wrapper<__libcpp_remove_reference_t<_Dp> >,
                                    _AllocT>
           _CntrlBlk;
       __cntrl_ = new _CntrlBlk(__r.get(), std::ref(__r.get_deleter()), _AllocT());
       __enable_weak_this(__r.get(), __r.get());
     }
     __r.release();
   }
 
   _LIBCPP_HIDE_FROM_ABI ~shared_ptr() {
     if (__cntrl_)
       __cntrl_->__release_shared();
   }
 
   _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>& operator=(const shared_ptr& __r) _NOEXCEPT {
     shared_ptr(__r).swap(*this);
     return *this;
   }
 
   template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
   _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>& operator=(const shared_ptr<_Yp>& __r) _NOEXCEPT {
     shared_ptr(__r).swap(*this);
     return *this;
   }
 
   _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>& operator=(shared_ptr&& __r) _NOEXCEPT {
     shared_ptr(std::move(__r)).swap(*this);
     return *this;
   }
 
   template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
   _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>& operator=(shared_ptr<_Yp>&& __r) {
     shared_ptr(std::move(__r)).swap(*this);
     return *this;
   }
 
 #if _LIBCPP_STD_VER <= 14 || defined(_LIBCPP_ENABLE_CXX17_REMOVED_AUTO_PTR)
   template <class _Yp,
             __enable_if_t<!is_array<_Yp>::value && is_convertible<_Yp*, typename shared_ptr<_Tp>::element_type*>::value,
                           int> = 0>
   _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>& operator=(auto_ptr<_Yp>&& __r) {
     shared_ptr(std::move(__r)).swap(*this);
     return *this;
   }
 #endif
 
   template <class _Yp,
             class _Dp,
             __enable_if_t<_And< __compatible_with<_Yp, _Tp>,
                                 is_convertible<typename unique_ptr<_Yp, _Dp>::pointer, element_type*> >::value,
                           int> = 0>
   _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>& operator=(unique_ptr<_Yp, _Dp>&& __r) {
     shared_ptr(std::move(__r)).swap(*this);
     return *this;
   }
 
   _LIBCPP_HIDE_FROM_ABI void swap(shared_ptr& __r) _NOEXCEPT {
     std::swap(__ptr_, __r.__ptr_);
     std::swap(__cntrl_, __r.__cntrl_);
   }
 
   _LIBCPP_HIDE_FROM_ABI void reset() _NOEXCEPT { shared_ptr().swap(*this); }
 
   template <class _Yp, __enable_if_t<__raw_pointer_compatible_with<_Yp, _Tp>::value, int> = 0>
   _LIBCPP_HIDE_FROM_ABI void reset(_Yp* __p) {
     shared_ptr(__p).swap(*this);
   }
 
   template <class _Yp, class _Dp, __enable_if_t<__shared_ptr_deleter_ctor_reqs<_Dp, _Yp, _Tp>::value, int> = 0>
   _LIBCPP_HIDE_FROM_ABI void reset(_Yp* __p, _Dp __d) {
     shared_ptr(__p, __d).swap(*this);
   }
 
   template <class _Yp,
             class _Dp,
             class _Alloc,
             __enable_if_t<__shared_ptr_deleter_ctor_reqs<_Dp, _Yp, _Tp>::value, int> = 0>
   _LIBCPP_HIDE_FROM_ABI void reset(_Yp* __p, _Dp __d, _Alloc __a) {
     shared_ptr(__p, __d, __a).swap(*this);
   }
 
   _LIBCPP_HIDE_FROM_ABI element_type* get() const _NOEXCEPT { return __ptr_; }
 
   _LIBCPP_HIDE_FROM_ABI __add_lvalue_reference_t<element_type> operator*() const _NOEXCEPT { return *__ptr_; }
 
   _LIBCPP_HIDE_FROM_ABI element_type* operator->() const _NOEXCEPT {
     static_assert(!is_array<_Tp>::value, "std::shared_ptr<T>::operator-> is only valid when T is not an array type.");
     return __ptr_;
   }
 
   _LIBCPP_HIDE_FROM_ABI long use_count() const _NOEXCEPT { return __cntrl_ ? __cntrl_->use_count() : 0; }
 
 #if _LIBCPP_STD_VER < 20 || defined(_LIBCPP_ENABLE_CXX20_REMOVED_SHARED_PTR_UNIQUE)
   _LIBCPP_DEPRECATED_IN_CXX17 _LIBCPP_HIDE_FROM_ABI bool unique() const _NOEXCEPT { return use_count() == 1; }
 #endif
 
   _LIBCPP_HIDE_FROM_ABI explicit operator bool() const _NOEXCEPT { return get() != nullptr; }
 
   template <class _Up>
   _LIBCPP_HIDE_FROM_ABI bool owner_before(shared_ptr<_Up> const& __p) const _NOEXCEPT {
     return __cntrl_ < __p.__cntrl_;
   }
 
   template <class _Up>
   _LIBCPP_HIDE_FROM_ABI bool owner_before(weak_ptr<_Up> const& __p) const _NOEXCEPT {
     return __cntrl_ < __p.__cntrl_;
   }
 
   _LIBCPP_HIDE_FROM_ABI bool __owner_equivalent(const shared_ptr& __p) const { return __cntrl_ == __p.__cntrl_; }
 
 #if _LIBCPP_STD_VER >= 17
   _LIBCPP_HIDE_FROM_ABI __add_lvalue_reference_t<element_type> operator[](ptrdiff_t __i) const {
     static_assert(is_array<_Tp>::value, "std::shared_ptr<T>::operator[] is only valid when T is an array type.");
     return __ptr_[__i];
   }
 #endif
 
 #if _LIBCPP_HAS_RTTI
   template <class _Dp>
   _LIBCPP_HIDE_FROM_ABI _Dp* __get_deleter() const _NOEXCEPT {
     return static_cast<_Dp*>(__cntrl_ ? const_cast<void*>(__cntrl_->__get_deleter(typeid(_Dp))) : nullptr);
   }
 #endif // _LIBCPP_HAS_RTTI
 
   template <class _Yp, class _CntrlBlk>
   _LIBCPP_HIDE_FROM_ABI static shared_ptr<_Tp> __create_with_control_block(_Yp* __p, _CntrlBlk* __cntrl) _NOEXCEPT {
     shared_ptr<_Tp> __r;
     __r.__ptr_   = __p;
     __r.__cntrl_ = __cntrl;
     __r.__enable_weak_this(__r.__ptr_, __r.__ptr_);
     return __r;
   }
 
 private:
   template <class _Yp, bool = is_function<_Yp>::value>
   struct __shared_ptr_default_allocator {
     typedef allocator<__remove_cv_t<_Yp> > type;
   };
 
   template <class _Yp>
   struct __shared_ptr_default_allocator<_Yp, true> {
     typedef allocator<__shared_ptr_dummy_rebind_allocator_type> type;
   };
 
   template <class _Yp,
             class _OrigPtr,
             __enable_if_t<is_convertible<_OrigPtr*, const enable_shared_from_this<_Yp>*>::value, int> = 0>
   _LIBCPP_HIDE_FROM_ABI void __enable_weak_this(const enable_shared_from_this<_Yp>* __e, _OrigPtr* __ptr) _NOEXCEPT {
     typedef __remove_cv_t<_Yp> _RawYp;
     if (__e && __e->__weak_this_.expired()) {
       __e->__weak_this_ = shared_ptr<_RawYp>(*this, const_cast<_RawYp*>(static_cast<const _Yp*>(__ptr)));
     }
   }
 
   _LIBCPP_HIDE_FROM_ABI void __enable_weak_this(...) _NOEXCEPT {}
 
   template <class, class _Yp>
   struct __shared_ptr_default_delete : default_delete<_Yp> {};
 
   template <class _Yp, class _Un, size_t _Sz>
   struct __shared_ptr_default_delete<_Yp[_Sz], _Un> : default_delete<_Yp[]> {};
 
   template <class _Yp, class _Un>
   struct __shared_ptr_default_delete<_Yp[], _Un> : default_delete<_Yp[]> {};
 
   template <class _Up>
   friend class _LIBCPP_TEMPLATE_VIS shared_ptr;
   template <class _Up>
   friend class _LIBCPP_TEMPLATE_VIS weak_ptr;
 };
 
 #if _LIBCPP_STD_VER >= 17
 template <class _Tp>
 shared_ptr(weak_ptr<_Tp>) -> shared_ptr<_Tp>;
 template <class _Tp, class _Dp>
 shared_ptr(unique_ptr<_Tp, _Dp>) -> shared_ptr<_Tp>;
 #endif
 
 //
 // std::allocate_shared and std::make_shared
 //
 template <class _Tp, class _Alloc, class... _Args, __enable_if_t<!is_array<_Tp>::value, int> = 0>
 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> allocate_shared(const _Alloc& __a, _Args&&... __args) {
   using _ControlBlock          = __shared_ptr_emplace<_Tp, _Alloc>;
   using _ControlBlockAllocator = typename __allocator_traits_rebind<_Alloc, _ControlBlock>::type;
   __allocation_guard<_ControlBlockAllocator> __guard(__a, 1);
   ::new ((void*)std::addressof(*__guard.__get())) _ControlBlock(__a, std::forward<_Args>(__args)...);
   auto __control_block = __guard.__release_ptr();
   return shared_ptr<_Tp>::__create_with_control_block(
       (*__control_block).__get_elem(), std::addressof(*__control_block));
 }
 
 template <class _Tp, class... _Args, __enable_if_t<!is_array<_Tp>::value, int> = 0>
 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared(_Args&&... __args) {
   return std::allocate_shared<_Tp>(allocator<__remove_cv_t<_Tp> >(), std::forward<_Args>(__args)...);
 }
 
 #if _LIBCPP_STD_VER >= 20
 
 template <class _Tp, class _Alloc, __enable_if_t<!is_array<_Tp>::value, int> = 0>
 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> allocate_shared_for_overwrite(const _Alloc& __a) {
   using _ForOverwriteAllocator = __allocator_traits_rebind_t<_Alloc, __for_overwrite_tag>;
   _ForOverwriteAllocator __alloc(__a);
   return std::allocate_shared<_Tp>(__alloc);
 }
 
 template <class _Tp, __enable_if_t<!is_array<_Tp>::value, int> = 0>
 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared_for_overwrite() {
   return std::allocate_shared_for_overwrite<_Tp>(allocator<__remove_cv_t<_Tp>>());
 }
 
 #endif // _LIBCPP_STD_VER >= 20
 
 #if _LIBCPP_STD_VER >= 17
 
 template <size_t _Alignment>
 struct __sp_aligned_storage {
   alignas(_Alignment) char __storage[_Alignment];
 };
 
 template <class _Tp, class _Alloc>
 struct __unbounded_array_control_block;
 
 template <class _Tp, class _Alloc>
 struct __unbounded_array_control_block<_Tp[], _Alloc> : __shared_weak_count {
   _LIBCPP_HIDE_FROM_ABI constexpr _Tp* __get_data() noexcept { return __data_; }
 
   _LIBCPP_HIDE_FROM_ABI explicit __unbounded_array_control_block(
       _Alloc const& __alloc, size_t __count, _Tp const& __arg)
       : __alloc_(__alloc), __count_(__count) {
     std::__uninitialized_allocator_fill_n_multidimensional(__alloc_, std::begin(__data_), __count_, __arg);
   }
 
   _LIBCPP_HIDE_FROM_ABI explicit __unbounded_array_control_block(_Alloc const& __alloc, size_t __count)
       : __alloc_(__alloc), __count_(__count) {
 #  if _LIBCPP_STD_VER >= 20
     if constexpr (is_same_v<typename _Alloc::value_type, __for_overwrite_tag>) {
       // We are purposefully not using an allocator-aware default construction because the spec says so.
       // There's currently no way of expressing default initialization in an allocator-aware manner anyway.
       std::uninitialized_default_construct_n(std::begin(__data_), __count_);
     } else {
       std::__uninitialized_allocator_value_construct_n_multidimensional(__alloc_, std::begin(__data_), __count_);
     }
 #  else
     std::__uninitialized_allocator_value_construct_n_multidimensional(__alloc_, std::begin(__data_), __count_);
 #  endif
   }
 
   // Returns the number of bytes required to store a control block followed by the given number
   // of elements of _Tp, with the whole storage being aligned to a multiple of _Tp's alignment.
   _LIBCPP_HIDE_FROM_ABI static constexpr size_t __bytes_for(size_t __elements) {
     // When there's 0 elements, the control block alone is enough since it holds one element.
     // Otherwise, we allocate one fewer element than requested because the control block already
     // holds one. Also, we use the bitwise formula below to ensure that we allocate enough bytes
     // for the whole allocation to be a multiple of _Tp's alignment. That formula is taken from [1].
     //
     // [1]: https://en.wikipedia.org/wiki/Data_structure_alignment#Computing_padding
     size_t __bytes           = __elements == 0 ? sizeof(__unbounded_array_control_block)
                                                : (__elements - 1) * sizeof(_Tp) + sizeof(__unbounded_array_control_block);
     constexpr size_t __align = alignof(_Tp);
     return (__bytes + __align - 1) & ~(__align - 1);
   }
 
   _LIBCPP_HIDE_FROM_ABI_VIRTUAL
   ~__unbounded_array_control_block() override {
   } // can't be `= default` because of the sometimes-non-trivial union member __data_
 
 private:
   _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared() _NOEXCEPT override {
 #  if _LIBCPP_STD_VER >= 20
     if constexpr (is_same_v<typename _Alloc::value_type, __for_overwrite_tag>) {
       std::__reverse_destroy(__data_, __data_ + __count_);
     } else {
       __allocator_traits_rebind_t<_Alloc, _Tp> __value_alloc(__alloc_);
       std::__allocator_destroy_multidimensional(__value_alloc, __data_, __data_ + __count_);
     }
 #  else
     __allocator_traits_rebind_t<_Alloc, _Tp> __value_alloc(__alloc_);
     std::__allocator_destroy_multidimensional(__value_alloc, __data_, __data_ + __count_);
 #  endif
   }
 
   _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared_weak() _NOEXCEPT override {
     using _AlignedStorage = __sp_aligned_storage<alignof(__unbounded_array_control_block)>;
     using _StorageAlloc   = __allocator_traits_rebind_t<_Alloc, _AlignedStorage>;
     using _PointerTraits  = pointer_traits<typename allocator_traits<_StorageAlloc>::pointer>;
 
     _StorageAlloc __tmp(__alloc_);
     __alloc_.~_Alloc();
     size_t __size              = __unbounded_array_control_block::__bytes_for(__count_);
     _AlignedStorage* __storage = reinterpret_cast<_AlignedStorage*>(this);
     allocator_traits<_StorageAlloc>::deallocate(
         __tmp, _PointerTraits::pointer_to(*__storage), __size / sizeof(_AlignedStorage));
   }
 
   _LIBCPP_NO_UNIQUE_ADDRESS _Alloc __alloc_;
   size_t __count_;
   union {
     _Tp __data_[1];
   };
 };
 
 template <class _Array, class _Alloc, class... _Arg>
 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Array>
 __allocate_shared_unbounded_array(const _Alloc& __a, size_t __n, _Arg&&... __arg) {
   static_assert(__is_unbounded_array_v<_Array>);
   // We compute the number of bytes necessary to hold the control block and the
   // array elements. Then, we allocate an array of properly-aligned dummy structs
   // large enough to hold the control block and array. This allows shifting the
   // burden of aligning memory properly from us to the allocator.
   using _ControlBlock   = __unbounded_array_control_block<_Array, _Alloc>;
   using _AlignedStorage = __sp_aligned_storage<alignof(_ControlBlock)>;
   using _StorageAlloc   = __allocator_traits_rebind_t<_Alloc, _AlignedStorage>;
   __allocation_guard<_StorageAlloc> __guard(__a, _ControlBlock::__bytes_for(__n) / sizeof(_AlignedStorage));
   _ControlBlock* __control_block = reinterpret_cast<_ControlBlock*>(std::addressof(*__guard.__get()));
   std::__construct_at(__control_block, __a, __n, std::forward<_Arg>(__arg)...);
   __guard.__release_ptr();
   return shared_ptr<_Array>::__create_with_control_block(__control_block->__get_data(), __control_block);
 }
 
 template <class _Tp, class _Alloc>
 struct __bounded_array_control_block;
 
 template <class _Tp, size_t _Count, class _Alloc>
 struct __bounded_array_control_block<_Tp[_Count], _Alloc> : __shared_weak_count {
   _LIBCPP_HIDE_FROM_ABI constexpr _Tp* __get_data() noexcept { return __data_; }
 
   _LIBCPP_HIDE_FROM_ABI explicit __bounded_array_control_block(_Alloc const& __alloc, _Tp const& __arg)
       : __alloc_(__alloc) {
     std::__uninitialized_allocator_fill_n_multidimensional(__alloc_, std::addressof(__data_[0]), _Count, __arg);
   }
 
   _LIBCPP_HIDE_FROM_ABI explicit __bounded_array_control_block(_Alloc const& __alloc) : __alloc_(__alloc) {
 #  if _LIBCPP_STD_VER >= 20
     if constexpr (is_same_v<typename _Alloc::value_type, __for_overwrite_tag>) {
       // We are purposefully not using an allocator-aware default construction because the spec says so.
       // There's currently no way of expressing default initialization in an allocator-aware manner anyway.
       std::uninitialized_default_construct_n(std::addressof(__data_[0]), _Count);
     } else {
       std::__uninitialized_allocator_value_construct_n_multidimensional(__alloc_, std::addressof(__data_[0]), _Count);
     }
 #  else
     std::__uninitialized_allocator_value_construct_n_multidimensional(__alloc_, std::addressof(__data_[0]), _Count);
 #  endif
   }
 
   _LIBCPP_HIDE_FROM_ABI_VIRTUAL
   ~__bounded_array_control_block() override {
   } // can't be `= default` because of the sometimes-non-trivial union member __data_
 
 private:
   _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared() _NOEXCEPT override {
 #  if _LIBCPP_STD_VER >= 20
     if constexpr (is_same_v<typename _Alloc::value_type, __for_overwrite_tag>) {
       std::__reverse_destroy(__data_, __data_ + _Count);
     } else {
       __allocator_traits_rebind_t<_Alloc, _Tp> __value_alloc(__alloc_);
       std::__allocator_destroy_multidimensional(__value_alloc, __data_, __data_ + _Count);
     }
 #  else
     __allocator_traits_rebind_t<_Alloc, _Tp> __value_alloc(__alloc_);
     std::__allocator_destroy_multidimensional(__value_alloc, __data_, __data_ + _Count);
 #  endif
   }
 
   _LIBCPP_HIDE_FROM_ABI_VIRTUAL void __on_zero_shared_weak() _NOEXCEPT override {
     using _ControlBlockAlloc = __allocator_traits_rebind_t<_Alloc, __bounded_array_control_block>;
     using _PointerTraits     = pointer_traits<typename allocator_traits<_ControlBlockAlloc>::pointer>;
 
     _ControlBlockAlloc __tmp(__alloc_);
     __alloc_.~_Alloc();
     allocator_traits<_ControlBlockAlloc>::deallocate(__tmp, _PointerTraits::pointer_to(*this), 1);
   }
 
   _LIBCPP_NO_UNIQUE_ADDRESS _Alloc __alloc_;
   union {
     _Tp __data_[_Count];
   };
 };
 
 template <class _Array, class _Alloc, class... _Arg>
 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Array> __allocate_shared_bounded_array(const _Alloc& __a, _Arg&&... __arg) {
   static_assert(__is_bounded_array_v<_Array>);
   using _ControlBlock      = __bounded_array_control_block<_Array, _Alloc>;
   using _ControlBlockAlloc = __allocator_traits_rebind_t<_Alloc, _ControlBlock>;
 
   __allocation_guard<_ControlBlockAlloc> __guard(__a, 1);
   _ControlBlock* __control_block = reinterpret_cast<_ControlBlock*>(std::addressof(*__guard.__get()));
   std::__construct_at(__control_block, __a, std::forward<_Arg>(__arg)...);
   __guard.__release_ptr();
   return shared_ptr<_Array>::__create_with_control_block(__control_block->__get_data(), __control_block);
 }
 
 #endif // _LIBCPP_STD_VER >= 17
 
 #if _LIBCPP_STD_VER >= 20
 
 // bounded array variants
 template <class _Tp, class _Alloc, __enable_if_t<is_bounded_array<_Tp>::value, int> = 0>
 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> allocate_shared(const _Alloc& __a) {
   return std::__allocate_shared_bounded_array<_Tp>(__a);
 }
 
 template <class _Tp, class _Alloc, __enable_if_t<is_bounded_array<_Tp>::value, int> = 0>
 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> allocate_shared(const _Alloc& __a, const remove_extent_t<_Tp>& __u) {
   return std::__allocate_shared_bounded_array<_Tp>(__a, __u);
 }
 
 template <class _Tp, class _Alloc, __enable_if_t<is_bounded_array<_Tp>::value, int> = 0>
 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> allocate_shared_for_overwrite(const _Alloc& __a) {
   using _ForOverwriteAllocator = __allocator_traits_rebind_t<_Alloc, __for_overwrite_tag>;
   _ForOverwriteAllocator __alloc(__a);
   return std::__allocate_shared_bounded_array<_Tp>(__alloc);
 }
 
 template <class _Tp, __enable_if_t<is_bounded_array<_Tp>::value, int> = 0>
 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared() {
   return std::__allocate_shared_bounded_array<_Tp>(allocator<_Tp>());
 }
 
 template <class _Tp, __enable_if_t<is_bounded_array<_Tp>::value, int> = 0>
 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared(const remove_extent_t<_Tp>& __u) {
   return std::__allocate_shared_bounded_array<_Tp>(allocator<_Tp>(), __u);
 }
 
 template <class _Tp, __enable_if_t<is_bounded_array<_Tp>::value, int> = 0>
 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared_for_overwrite() {
   return std::__allocate_shared_bounded_array<_Tp>(allocator<__for_overwrite_tag>());
 }
 
 // unbounded array variants
 template <class _Tp, class _Alloc, __enable_if_t<is_unbounded_array<_Tp>::value, int> = 0>
 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> allocate_shared(const _Alloc& __a, size_t __n) {
   return std::__allocate_shared_unbounded_array<_Tp>(__a, __n);
 }
 
 template <class _Tp, class _Alloc, __enable_if_t<is_unbounded_array<_Tp>::value, int> = 0>
 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> allocate_shared(const _Alloc& __a, size_t __n, const remove_extent_t<_Tp>& __u) {
   return std::__allocate_shared_unbounded_array<_Tp>(__a, __n, __u);
 }
 
 template <class _Tp, class _Alloc, __enable_if_t<is_unbounded_array<_Tp>::value, int> = 0>
 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> allocate_shared_for_overwrite(const _Alloc& __a, size_t __n) {
   using _ForOverwriteAllocator = __allocator_traits_rebind_t<_Alloc, __for_overwrite_tag>;
   _ForOverwriteAllocator __alloc(__a);
   return std::__allocate_shared_unbounded_array<_Tp>(__alloc, __n);
 }
 
 template <class _Tp, __enable_if_t<is_unbounded_array<_Tp>::value, int> = 0>
 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared(size_t __n) {
   return std::__allocate_shared_unbounded_array<_Tp>(allocator<_Tp>(), __n);
 }
 
 template <class _Tp, __enable_if_t<is_unbounded_array<_Tp>::value, int> = 0>
 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared(size_t __n, const remove_extent_t<_Tp>& __u) {
   return std::__allocate_shared_unbounded_array<_Tp>(allocator<_Tp>(), __n, __u);
 }
 
 template <class _Tp, __enable_if_t<is_unbounded_array<_Tp>::value, int> = 0>
 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> make_shared_for_overwrite(size_t __n) {
   return std::__allocate_shared_unbounded_array<_Tp>(allocator<__for_overwrite_tag>(), __n);
 }
 
 #endif // _LIBCPP_STD_VER >= 20
 
 template <class _Tp, class _Up>
 inline _LIBCPP_HIDE_FROM_ABI bool operator==(const shared_ptr<_Tp>& __x, const shared_ptr<_Up>& __y) _NOEXCEPT {
   return __x.get() == __y.get();
 }
 
 #if _LIBCPP_STD_VER <= 17
 
 template <class _Tp, class _Up>
 inline _LIBCPP_HIDE_FROM_ABI bool operator!=(const shared_ptr<_Tp>& __x, const shared_ptr<_Up>& __y) _NOEXCEPT {
   return !(__x == __y);
 }
 
 template <class _Tp, class _Up>
 inline _LIBCPP_HIDE_FROM_ABI bool operator<(const shared_ptr<_Tp>& __x, const shared_ptr<_Up>& __y) _NOEXCEPT {
 #  if _LIBCPP_STD_VER <= 11
   typedef typename common_type<_Tp*, _Up*>::type _Vp;
   return less<_Vp>()(__x.get(), __y.get());
 #  else
   return less<>()(__x.get(), __y.get());
 #  endif
 }
 
 template <class _Tp, class _Up>
 inline _LIBCPP_HIDE_FROM_ABI bool operator>(const shared_ptr<_Tp>& __x, const shared_ptr<_Up>& __y) _NOEXCEPT {
   return __y < __x;
 }
 
 template <class _Tp, class _Up>
 inline _LIBCPP_HIDE_FROM_ABI bool operator<=(const shared_ptr<_Tp>& __x, const shared_ptr<_Up>& __y) _NOEXCEPT {
   return !(__y < __x);
 }
 
 template <class _Tp, class _Up>
 inline _LIBCPP_HIDE_FROM_ABI bool operator>=(const shared_ptr<_Tp>& __x, const shared_ptr<_Up>& __y) _NOEXCEPT {
   return !(__x < __y);
 }
 
 #endif // _LIBCPP_STD_VER <= 17
 
 #if _LIBCPP_STD_VER >= 20
 template <class _Tp, class _Up>
 _LIBCPP_HIDE_FROM_ABI strong_ordering operator<=>(shared_ptr<_Tp> const& __x, shared_ptr<_Up> const& __y) noexcept {
   return compare_three_way()(__x.get(), __y.get());
 }
 #endif
 
 template <class _Tp>
 inline _LIBCPP_HIDE_FROM_ABI bool operator==(const shared_ptr<_Tp>& __x, nullptr_t) _NOEXCEPT {
   return !__x;
 }
 
 #if _LIBCPP_STD_VER <= 17
 
 template <class _Tp>
 inline _LIBCPP_HIDE_FROM_ABI bool operator==(nullptr_t, const shared_ptr<_Tp>& __x) _NOEXCEPT {
   return !__x;
 }
 
 template <class _Tp>
 inline _LIBCPP_HIDE_FROM_ABI bool operator!=(const shared_ptr<_Tp>& __x, nullptr_t) _NOEXCEPT {
   return static_cast<bool>(__x);
 }
 
 template <class _Tp>
 inline _LIBCPP_HIDE_FROM_ABI bool operator!=(nullptr_t, const shared_ptr<_Tp>& __x) _NOEXCEPT {
   return static_cast<bool>(__x);
 }
 
 template <class _Tp>
 inline _LIBCPP_HIDE_FROM_ABI bool operator<(const shared_ptr<_Tp>& __x, nullptr_t) _NOEXCEPT {
   return less<typename shared_ptr<_Tp>::element_type*>()(__x.get(), nullptr);
 }
 
 template <class _Tp>
 inline _LIBCPP_HIDE_FROM_ABI bool operator<(nullptr_t, const shared_ptr<_Tp>& __x) _NOEXCEPT {
   return less<typename shared_ptr<_Tp>::element_type*>()(nullptr, __x.get());
 }
 
 template <class _Tp>
 inline _LIBCPP_HIDE_FROM_ABI bool operator>(const shared_ptr<_Tp>& __x, nullptr_t) _NOEXCEPT {
   return nullptr < __x;
 }
 
 template <class _Tp>
 inline _LIBCPP_HIDE_FROM_ABI bool operator>(nullptr_t, const shared_ptr<_Tp>& __x) _NOEXCEPT {
   return __x < nullptr;
 }
 
 template <class _Tp>
 inline _LIBCPP_HIDE_FROM_ABI bool operator<=(const shared_ptr<_Tp>& __x, nullptr_t) _NOEXCEPT {
   return !(nullptr < __x);
 }
 
 template <class _Tp>
 inline _LIBCPP_HIDE_FROM_ABI bool operator<=(nullptr_t, const shared_ptr<_Tp>& __x) _NOEXCEPT {
   return !(__x < nullptr);
 }
 
 template <class _Tp>
 inline _LIBCPP_HIDE_FROM_ABI bool operator>=(const shared_ptr<_Tp>& __x, nullptr_t) _NOEXCEPT {
   return !(__x < nullptr);
 }
 
 template <class _Tp>
 inline _LIBCPP_HIDE_FROM_ABI bool operator>=(nullptr_t, const shared_ptr<_Tp>& __x) _NOEXCEPT {
   return !(nullptr < __x);
 }
 
 #endif // _LIBCPP_STD_VER <= 17
 
 #if _LIBCPP_STD_VER >= 20
 template <class _Tp>
 _LIBCPP_HIDE_FROM_ABI strong_ordering operator<=>(shared_ptr<_Tp> const& __x, nullptr_t) noexcept {
   return compare_three_way()(__x.get(), static_cast<typename shared_ptr<_Tp>::element_type*>(nullptr));
 }
 #endif
 
 template <class _Tp>
 inline _LIBCPP_HIDE_FROM_ABI void swap(shared_ptr<_Tp>& __x, shared_ptr<_Tp>& __y) _NOEXCEPT {
   __x.swap(__y);
 }
 
 template <class _Tp, class _Up>
 inline _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> static_pointer_cast(const shared_ptr<_Up>& __r) _NOEXCEPT {
   return shared_ptr<_Tp>(__r, static_cast< typename shared_ptr<_Tp>::element_type*>(__r.get()));
 }
 
 // LWG-2996
 // We don't backport because it is an evolutionary change.
 #if _LIBCPP_STD_VER >= 20
 template <class _Tp, class _Up>
 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> static_pointer_cast(shared_ptr<_Up>&& __r) noexcept {
   return shared_ptr<_Tp>(std::move(__r), static_cast<typename shared_ptr<_Tp>::element_type*>(__r.get()));
 }
 #endif
 
 template <class _Tp, class _Up>
 inline _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> dynamic_pointer_cast(const shared_ptr<_Up>& __r) _NOEXCEPT {
   typedef typename shared_ptr<_Tp>::element_type _ET;
   _ET* __p = dynamic_cast<_ET*>(__r.get());
   return __p ? shared_ptr<_Tp>(__r, __p) : shared_ptr<_Tp>();
 }
 
 // LWG-2996
 // We don't backport because it is an evolutionary change.
 #if _LIBCPP_STD_VER >= 20
 template <class _Tp, class _Up>
 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> dynamic_pointer_cast(shared_ptr<_Up>&& __r) noexcept {
   auto* __p = dynamic_cast<typename shared_ptr<_Tp>::element_type*>(__r.get());
   return __p ? shared_ptr<_Tp>(std::move(__r), __p) : shared_ptr<_Tp>();
 }
 #endif
 
 template <class _Tp, class _Up>
 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> const_pointer_cast(const shared_ptr<_Up>& __r) _NOEXCEPT {
   typedef typename shared_ptr<_Tp>::element_type _RTp;
   return shared_ptr<_Tp>(__r, const_cast<_RTp*>(__r.get()));
 }
 
 // LWG-2996
 // We don't backport because it is an evolutionary change.
 #if _LIBCPP_STD_VER >= 20
 template <class _Tp, class _Up>
 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> const_pointer_cast(shared_ptr<_Up>&& __r) noexcept {
   return shared_ptr<_Tp>(std::move(__r), const_cast<typename shared_ptr<_Tp>::element_type*>(__r.get()));
 }
 #endif
 
 template <class _Tp, class _Up>
 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> reinterpret_pointer_cast(const shared_ptr<_Up>& __r) _NOEXCEPT {
   return shared_ptr<_Tp>(__r, reinterpret_cast< typename shared_ptr<_Tp>::element_type*>(__r.get()));
 }
 
 // LWG-2996
 // We don't backport because it is an evolutionary change.
 #if _LIBCPP_STD_VER >= 20
 template <class _Tp, class _Up>
 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> reinterpret_pointer_cast(shared_ptr<_Up>&& __r) noexcept {
   return shared_ptr<_Tp>(std::move(__r), reinterpret_cast<typename shared_ptr<_Tp>::element_type*>(__r.get()));
 }
 #endif
 
 #if _LIBCPP_HAS_RTTI
 
 template <class _Dp, class _Tp>
 inline _LIBCPP_HIDE_FROM_ABI _Dp* get_deleter(const shared_ptr<_Tp>& __p) _NOEXCEPT {
   return __p.template __get_deleter<_Dp>();
 }
 
 #endif // _LIBCPP_HAS_RTTI
 
 template <class _Tp>
 class _LIBCPP_SHARED_PTR_TRIVIAL_ABI _LIBCPP_TEMPLATE_VIS weak_ptr {
 public:
 #if _LIBCPP_STD_VER >= 17
   typedef remove_extent_t<_Tp> element_type;
 #else
   typedef _Tp element_type;
 #endif
 
   // A weak_ptr contains only two raw pointers which point to the heap and move constructing already doesn't require
   // any bookkeeping, so it's always trivially relocatable.
   using __trivially_relocatable _LIBCPP_NODEBUG = weak_ptr;
 
 private:
   element_type* __ptr_;
   __shared_weak_count* __cntrl_;
 
 public:
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR weak_ptr() _NOEXCEPT;
 
   template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
   _LIBCPP_HIDE_FROM_ABI weak_ptr(shared_ptr<_Yp> const& __r) _NOEXCEPT;
 
   _LIBCPP_HIDE_FROM_ABI weak_ptr(weak_ptr const& __r) _NOEXCEPT;
 
   template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
   _LIBCPP_HIDE_FROM_ABI weak_ptr(weak_ptr<_Yp> const& __r) _NOEXCEPT;
 
   _LIBCPP_HIDE_FROM_ABI weak_ptr(weak_ptr&& __r) _NOEXCEPT;
 
   template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
   _LIBCPP_HIDE_FROM_ABI weak_ptr(weak_ptr<_Yp>&& __r) _NOEXCEPT;
 
   _LIBCPP_HIDE_FROM_ABI ~weak_ptr();
 
   _LIBCPP_HIDE_FROM_ABI weak_ptr& operator=(weak_ptr const& __r) _NOEXCEPT;
   template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
   _LIBCPP_HIDE_FROM_ABI weak_ptr& operator=(weak_ptr<_Yp> const& __r) _NOEXCEPT;
 
   _LIBCPP_HIDE_FROM_ABI weak_ptr& operator=(weak_ptr&& __r) _NOEXCEPT;
   template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
   _LIBCPP_HIDE_FROM_ABI weak_ptr& operator=(weak_ptr<_Yp>&& __r) _NOEXCEPT;
 
   template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> = 0>
   _LIBCPP_HIDE_FROM_ABI weak_ptr& operator=(shared_ptr<_Yp> const& __r) _NOEXCEPT;
 
   _LIBCPP_HIDE_FROM_ABI void swap(weak_ptr& __r) _NOEXCEPT;
   _LIBCPP_HIDE_FROM_ABI void reset() _NOEXCEPT;
 
   _LIBCPP_HIDE_FROM_ABI long use_count() const _NOEXCEPT { return __cntrl_ ? __cntrl_->use_count() : 0; }
   _LIBCPP_HIDE_FROM_ABI bool expired() const _NOEXCEPT { return __cntrl_ == nullptr || __cntrl_->use_count() == 0; }
   _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> lock() const _NOEXCEPT;
   template <class _Up>
   _LIBCPP_HIDE_FROM_ABI bool owner_before(const shared_ptr<_Up>& __r) const _NOEXCEPT {
     return __cntrl_ < __r.__cntrl_;
   }
   template <class _Up>
   _LIBCPP_HIDE_FROM_ABI bool owner_before(const weak_ptr<_Up>& __r) const _NOEXCEPT {
     return __cntrl_ < __r.__cntrl_;
   }
 
   template <class _Up>
   friend class _LIBCPP_TEMPLATE_VIS weak_ptr;
   template <class _Up>
   friend class _LIBCPP_TEMPLATE_VIS shared_ptr;
 };
 
 #if _LIBCPP_STD_VER >= 17
 template <class _Tp>
 weak_ptr(shared_ptr<_Tp>) -> weak_ptr<_Tp>;
 #endif
 
 template <class _Tp>
 inline _LIBCPP_CONSTEXPR weak_ptr<_Tp>::weak_ptr() _NOEXCEPT : __ptr_(nullptr), __cntrl_(nullptr) {}
 
 template <class _Tp>
 inline weak_ptr<_Tp>::weak_ptr(weak_ptr const& __r) _NOEXCEPT : __ptr_(__r.__ptr_), __cntrl_(__r.__cntrl_) {
   if (__cntrl_)
     __cntrl_->__add_weak();
 }
 
 template <class _Tp>
 template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> >
 inline weak_ptr<_Tp>::weak_ptr(shared_ptr<_Yp> const& __r) _NOEXCEPT : __ptr_(__r.__ptr_), __cntrl_(__r.__cntrl_) {
   if (__cntrl_)
     __cntrl_->__add_weak();
 }
 
 template <class _Tp>
 template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> >
 inline weak_ptr<_Tp>::weak_ptr(weak_ptr<_Yp> const& __r) _NOEXCEPT : __ptr_(nullptr), __cntrl_(nullptr) {
   shared_ptr<_Yp> __s = __r.lock();
   *this               = weak_ptr<_Tp>(__s);
 }
 
 template <class _Tp>
 inline weak_ptr<_Tp>::weak_ptr(weak_ptr&& __r) _NOEXCEPT : __ptr_(__r.__ptr_), __cntrl_(__r.__cntrl_) {
   __r.__ptr_   = nullptr;
   __r.__cntrl_ = nullptr;
 }
 
 template <class _Tp>
 template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> >
 inline weak_ptr<_Tp>::weak_ptr(weak_ptr<_Yp>&& __r) _NOEXCEPT : __ptr_(nullptr), __cntrl_(nullptr) {
   shared_ptr<_Yp> __s = __r.lock();
   *this               = weak_ptr<_Tp>(__s);
   __r.reset();
 }
 
 template <class _Tp>
 weak_ptr<_Tp>::~weak_ptr() {
   if (__cntrl_)
     __cntrl_->__release_weak();
 }
 
 template <class _Tp>
 inline weak_ptr<_Tp>& weak_ptr<_Tp>::operator=(weak_ptr const& __r) _NOEXCEPT {
   weak_ptr(__r).swap(*this);
   return *this;
 }
 
 template <class _Tp>
 template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> >
 inline weak_ptr<_Tp>& weak_ptr<_Tp>::operator=(weak_ptr<_Yp> const& __r) _NOEXCEPT {
   weak_ptr(__r).swap(*this);
   return *this;
 }
 
 template <class _Tp>
 inline weak_ptr<_Tp>& weak_ptr<_Tp>::operator=(weak_ptr&& __r) _NOEXCEPT {
   weak_ptr(std::move(__r)).swap(*this);
   return *this;
 }
 
 template <class _Tp>
 template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> >
 inline weak_ptr<_Tp>& weak_ptr<_Tp>::operator=(weak_ptr<_Yp>&& __r) _NOEXCEPT {
   weak_ptr(std::move(__r)).swap(*this);
   return *this;
 }
 
 template <class _Tp>
 template <class _Yp, __enable_if_t<__compatible_with<_Yp, _Tp>::value, int> >
 inline weak_ptr<_Tp>& weak_ptr<_Tp>::operator=(shared_ptr<_Yp> const& __r) _NOEXCEPT {
   weak_ptr(__r).swap(*this);
   return *this;
 }
 
 template <class _Tp>
 inline void weak_ptr<_Tp>::swap(weak_ptr& __r) _NOEXCEPT {
   std::swap(__ptr_, __r.__ptr_);
   std::swap(__cntrl_, __r.__cntrl_);
 }
 
 template <class _Tp>
 inline _LIBCPP_HIDE_FROM_ABI void swap(weak_ptr<_Tp>& __x, weak_ptr<_Tp>& __y) _NOEXCEPT {
   __x.swap(__y);
 }
 
 template <class _Tp>
 inline void weak_ptr<_Tp>::reset() _NOEXCEPT {
   weak_ptr().swap(*this);
 }
 
 template <class _Tp>
 shared_ptr<_Tp> weak_ptr<_Tp>::lock() const _NOEXCEPT {
   shared_ptr<_Tp> __r;
   __r.__cntrl_ = __cntrl_ ? __cntrl_->lock() : __cntrl_;
   if (__r.__cntrl_)
     __r.__ptr_ = __ptr_;
   return __r;
 }
 
 #if _LIBCPP_STD_VER >= 17
 template <class _Tp = void>
 struct owner_less;
 #else
 template <class _Tp>
 struct owner_less;
 #endif
 
 template <class _Tp>
 struct _LIBCPP_TEMPLATE_VIS owner_less<shared_ptr<_Tp> > : __binary_function<shared_ptr<_Tp>, shared_ptr<_Tp>, bool> {
   _LIBCPP_HIDE_FROM_ABI bool operator()(shared_ptr<_Tp> const& __x, shared_ptr<_Tp> const& __y) const _NOEXCEPT {
     return __x.owner_before(__y);
   }
   _LIBCPP_HIDE_FROM_ABI bool operator()(shared_ptr<_Tp> const& __x, weak_ptr<_Tp> const& __y) const _NOEXCEPT {
     return __x.owner_before(__y);
   }
   _LIBCPP_HIDE_FROM_ABI bool operator()(weak_ptr<_Tp> const& __x, shared_ptr<_Tp> const& __y) const _NOEXCEPT {
     return __x.owner_before(__y);
   }
 };
 
 template <class _Tp>
 struct _LIBCPP_TEMPLATE_VIS owner_less<weak_ptr<_Tp> > : __binary_function<weak_ptr<_Tp>, weak_ptr<_Tp>, bool> {
   _LIBCPP_HIDE_FROM_ABI bool operator()(weak_ptr<_Tp> const& __x, weak_ptr<_Tp> const& __y) const _NOEXCEPT {
     return __x.owner_before(__y);
   }
   _LIBCPP_HIDE_FROM_ABI bool operator()(shared_ptr<_Tp> const& __x, weak_ptr<_Tp> const& __y) const _NOEXCEPT {
     return __x.owner_before(__y);
   }
   _LIBCPP_HIDE_FROM_ABI bool operator()(weak_ptr<_Tp> const& __x, shared_ptr<_Tp> const& __y) const _NOEXCEPT {
     return __x.owner_before(__y);
   }
 };
 
 #if _LIBCPP_STD_VER >= 17
 template <>
 struct _LIBCPP_TEMPLATE_VIS owner_less<void> {
   template <class _Tp, class _Up>
   _LIBCPP_HIDE_FROM_ABI bool operator()(shared_ptr<_Tp> const& __x, shared_ptr<_Up> const& __y) const _NOEXCEPT {
     return __x.owner_before(__y);
   }
   template <class _Tp, class _Up>
   _LIBCPP_HIDE_FROM_ABI bool operator()(shared_ptr<_Tp> const& __x, weak_ptr<_Up> const& __y) const _NOEXCEPT {
     return __x.owner_before(__y);
   }
   template <class _Tp, class _Up>
   _LIBCPP_HIDE_FROM_ABI bool operator()(weak_ptr<_Tp> const& __x, shared_ptr<_Up> const& __y) const _NOEXCEPT {
     return __x.owner_before(__y);
   }
   template <class _Tp, class _Up>
   _LIBCPP_HIDE_FROM_ABI bool operator()(weak_ptr<_Tp> const& __x, weak_ptr<_Up> const& __y) const _NOEXCEPT {
     return __x.owner_before(__y);
   }
   typedef void is_transparent;
 };
 #endif
 
 template <class _Tp>
 class _LIBCPP_TEMPLATE_VIS enable_shared_from_this {
   mutable weak_ptr<_Tp> __weak_this_;
 
 protected:
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR enable_shared_from_this() _NOEXCEPT {}
   _LIBCPP_HIDE_FROM_ABI enable_shared_from_this(enable_shared_from_this const&) _NOEXCEPT {}
   _LIBCPP_HIDE_FROM_ABI enable_shared_from_this& operator=(enable_shared_from_this const&) _NOEXCEPT { return *this; }
   _LIBCPP_HIDE_FROM_ABI ~enable_shared_from_this() {}
 
 public:
   _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> shared_from_this() { return shared_ptr<_Tp>(__weak_this_); }
   _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp const> shared_from_this() const { return shared_ptr<const _Tp>(__weak_this_); }
 
 #if _LIBCPP_STD_VER >= 17
   _LIBCPP_HIDE_FROM_ABI weak_ptr<_Tp> weak_from_this() _NOEXCEPT { return __weak_this_; }
 
   _LIBCPP_HIDE_FROM_ABI weak_ptr<const _Tp> weak_from_this() const _NOEXCEPT { return __weak_this_; }
 #endif // _LIBCPP_STD_VER >= 17
 
   template <class _Up>
   friend class shared_ptr;
 };
 
 template <class _Tp>
 struct _LIBCPP_TEMPLATE_VIS hash;
 
 template <class _Tp>
 struct _LIBCPP_TEMPLATE_VIS hash<shared_ptr<_Tp> > {
 #if _LIBCPP_STD_VER <= 17 || defined(_LIBCPP_ENABLE_CXX20_REMOVED_BINDER_TYPEDEFS)
   _LIBCPP_DEPRECATED_IN_CXX17 typedef shared_ptr<_Tp> argument_type;
   _LIBCPP_DEPRECATED_IN_CXX17 typedef size_t result_type;
 #endif
 
   _LIBCPP_HIDE_FROM_ABI size_t operator()(const shared_ptr<_Tp>& __ptr) const _NOEXCEPT {
     return hash<typename shared_ptr<_Tp>::element_type*>()(__ptr.get());
   }
 };
 
 template <class _CharT, class _Traits, class _Yp>
 inline _LIBCPP_HIDE_FROM_ABI basic_ostream<_CharT, _Traits>&
 operator<<(basic_ostream<_CharT, _Traits>& __os, shared_ptr<_Yp> const& __p);
 
 #if _LIBCPP_HAS_THREADS
 
 class _LIBCPP_EXPORTED_FROM_ABI __sp_mut {
   void* __lx_;
 
 public:
   void lock() _NOEXCEPT;
   void unlock() _NOEXCEPT;
 
 private:
   _LIBCPP_CONSTEXPR __sp_mut(void*) _NOEXCEPT;
   __sp_mut(const __sp_mut&);
   __sp_mut& operator=(const __sp_mut&);
 
   friend _LIBCPP_EXPORTED_FROM_ABI __sp_mut& __get_sp_mut(const void*);
 };
 
 _LIBCPP_EXPORTED_FROM_ABI __sp_mut& __get_sp_mut(const void*);
 
 template <class _Tp>
 inline _LIBCPP_HIDE_FROM_ABI bool atomic_is_lock_free(const shared_ptr<_Tp>*) {
   return false;
 }
 
 template <class _Tp>
 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> atomic_load(const shared_ptr<_Tp>* __p) {
   __sp_mut& __m = std::__get_sp_mut(__p);
   __m.lock();
   shared_ptr<_Tp> __q = *__p;
   __m.unlock();
   return __q;
 }
 
 template <class _Tp>
 inline _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> atomic_load_explicit(const shared_ptr<_Tp>* __p, memory_order) {
   return std::atomic_load(__p);
 }
 
 template <class _Tp>
 _LIBCPP_HIDE_FROM_ABI void atomic_store(shared_ptr<_Tp>* __p, shared_ptr<_Tp> __r) {
   __sp_mut& __m = std::__get_sp_mut(__p);
   __m.lock();
   __p->swap(__r);
   __m.unlock();
 }
 
 template <class _Tp>
 inline _LIBCPP_HIDE_FROM_ABI void atomic_store_explicit(shared_ptr<_Tp>* __p, shared_ptr<_Tp> __r, memory_order) {
   std::atomic_store(__p, __r);
 }
 
 template <class _Tp>
 _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp> atomic_exchange(shared_ptr<_Tp>* __p, shared_ptr<_Tp> __r) {
   __sp_mut& __m = std::__get_sp_mut(__p);
   __m.lock();
   __p->swap(__r);
   __m.unlock();
   return __r;
 }
 
 template <class _Tp>
 inline _LIBCPP_HIDE_FROM_ABI shared_ptr<_Tp>
 atomic_exchange_explicit(shared_ptr<_Tp>* __p, shared_ptr<_Tp> __r, memory_order) {
   return std::atomic_exchange(__p, __r);
 }
 
 template <class _Tp>
 _LIBCPP_HIDE_FROM_ABI bool
 atomic_compare_exchange_strong(shared_ptr<_Tp>* __p, shared_ptr<_Tp>* __v, shared_ptr<_Tp> __w) {
   shared_ptr<_Tp> __temp;
   __sp_mut& __m = std::__get_sp_mut(__p);
   __m.lock();
   if (__p->__owner_equivalent(*__v)) {
     std::swap(__temp, *__p);
     *__p = __w;
     __m.unlock();
     return true;
   }
   std::swap(__temp, *__v);
   *__v = *__p;
   __m.unlock();
   return false;
 }
 
 template <class _Tp>
 inline _LIBCPP_HIDE_FROM_ABI bool
 atomic_compare_exchange_weak(shared_ptr<_Tp>* __p, shared_ptr<_Tp>* __v, shared_ptr<_Tp> __w) {
   return std::atomic_compare_exchange_strong(__p, __v, __w);
 }
 
 template <class _Tp>
 inline _LIBCPP_HIDE_FROM_ABI bool atomic_compare_exchange_strong_explicit(
     shared_ptr<_Tp>* __p, shared_ptr<_Tp>* __v, shared_ptr<_Tp> __w, memory_order, memory_order) {
   return std::atomic_compare_exchange_strong(__p, __v, __w);
 }
 
 template <class _Tp>
 inline _LIBCPP_HIDE_FROM_ABI bool atomic_compare_exchange_weak_explicit(
     shared_ptr<_Tp>* __p, shared_ptr<_Tp>* __v, shared_ptr<_Tp> __w, memory_order, memory_order) {
   return std::atomic_compare_exchange_weak(__p, __v, __w);
 }
 
 #endif // _LIBCPP_HAS_THREADS
 
 _LIBCPP_END_NAMESPACE_STD
 
 _LIBCPP_POP_MACROS
 
 #endif // _LIBCPP___MEMORY_SHARED_PTR_H

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