libcxx/include/__memory/compressed_pair.h

   1 // -*- C++ -*-
   2 //===----------------------------------------------------------------------===//
   3 //
   4 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   5 // See https://llvm.org/LICENSE.txt for license information.
   6 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   7 //
   8 //===----------------------------------------------------------------------===//
   9
  10 #ifndef _LIBCPP___MEMORY_COMPRESSED_PAIR_H
  11 #define _LIBCPP___MEMORY_COMPRESSED_PAIR_H
  12
  13 #include <__config>
  14 #include <__utility/forward.h>
  15 #include <tuple> // needed in c++03 for some constructors
  16 #include <type_traits>
  17 #include <utility>
  18
  19 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  20 #pragma GCC system_header
  21 #endif
  22
  23 _LIBCPP_BEGIN_NAMESPACE_STD
  24
  25 // Tag used to default initialize one or both of the pair's elements.
  26 struct __default_init_tag {};
  27 struct __value_init_tag {};
  28
  29 template <class _Tp, int _Idx,
  30           bool _CanBeEmptyBase =
  31               is_empty<_Tp>::value && !__libcpp_is_final<_Tp>::value>
  32 struct __compressed_pair_elem {
  33   typedef _Tp _ParamT;
  34   typedef _Tp& reference;
  35   typedef const _Tp& const_reference;
  36
  37   _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
  38   __compressed_pair_elem(__default_init_tag) {}
  39   _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
  40   __compressed_pair_elem(__value_init_tag) : __value_() {}
  41
  42   template <class _Up, class = typename enable_if<
  43       !is_same<__compressed_pair_elem, typename decay<_Up>::type>::value
  44   >::type>
  45   _LIBCPP_INLINE_VISIBILITY
  46   _LIBCPP_CONSTEXPR explicit
  47   __compressed_pair_elem(_Up&& __u)
  48       : __value_(_VSTD::forward<_Up>(__u))
  49     {
  50     }
  51
  52
  53 #ifndef _LIBCPP_CXX03_LANG
  54   template <class... _Args, size_t... _Indexes>
  55   _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
  56   __compressed_pair_elem(piecewise_construct_t, tuple<_Args...> __args,
  57                          __tuple_indices<_Indexes...>)
  58       : __value_(_VSTD::forward<_Args>(_VSTD::get<_Indexes>(__args))...) {}
  59 #endif
  60
  61   _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11 reference __get() _NOEXCEPT { return __value_; }
  62   _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR const_reference __get() const _NOEXCEPT { return __value_; }
  63
  64 private:
  65   _Tp __value_;
  66 };
  67
  68 template <class _Tp, int _Idx>
  69 struct __compressed_pair_elem<_Tp, _Idx, true> : private _Tp {
  70   typedef _Tp _ParamT;
  71   typedef _Tp& reference;
  72   typedef const _Tp& const_reference;
  73   typedef _Tp __value_type;
  74
  75   _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR __compressed_pair_elem() = default;
  76   _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
  77   __compressed_pair_elem(__default_init_tag) {}
  78   _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
  79   __compressed_pair_elem(__value_init_tag) : __value_type() {}
  80
  81   template <class _Up, class = typename enable_if<
  82         !is_same<__compressed_pair_elem, typename decay<_Up>::type>::value
  83   >::type>
  84   _LIBCPP_INLINE_VISIBILITY
  85   _LIBCPP_CONSTEXPR explicit
  86   __compressed_pair_elem(_Up&& __u)
  87       : __value_type(_VSTD::forward<_Up>(__u))
  88   {}
  89
  90 #ifndef _LIBCPP_CXX03_LANG
  91   template <class... _Args, size_t... _Indexes>
  92   _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
  93   __compressed_pair_elem(piecewise_construct_t, tuple<_Args...> __args,
  94                          __tuple_indices<_Indexes...>)
  95       : __value_type(_VSTD::forward<_Args>(_VSTD::get<_Indexes>(__args))...) {}
  96 #endif
  97
  98   _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11 reference __get() _NOEXCEPT { return *this; }
  99   _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR const_reference __get() const _NOEXCEPT { return *this; }
 100 };
 101
 102 template <class _T1, class _T2>
 103 class __compressed_pair : private __compressed_pair_elem<_T1, 0>,
 104                           private __compressed_pair_elem<_T2, 1> {
 105 public:
 106   // NOTE: This static assert should never fire because __compressed_pair
 107   // is *almost never* used in a scenario where it's possible for T1 == T2.
 108   // (The exception is std::function where it is possible that the function
 109   //  object and the allocator have the same type).
 110   static_assert((!is_same<_T1, _T2>::value),
 111     "__compressed_pair cannot be instantiated when T1 and T2 are the same type; "
 112     "The current implementation is NOT ABI-compatible with the previous "
 113     "implementation for this configuration");
 114
 115     typedef _LIBCPP_NODEBUG __compressed_pair_elem<_T1, 0> _Base1;
 116     typedef _LIBCPP_NODEBUG __compressed_pair_elem<_T2, 1> _Base2;
 117
 118     template <bool _Dummy = true,
 119       class = typename enable_if<
 120           __dependent_type<is_default_constructible<_T1>, _Dummy>::value &&
 121           __dependent_type<is_default_constructible<_T2>, _Dummy>::value
 122       >::type
 123   >
 124   _LIBCPP_INLINE_VISIBILITY
 125   _LIBCPP_CONSTEXPR __compressed_pair() : _Base1(__value_init_tag()), _Base2(__value_init_tag()) {}
 126
 127   template <class _U1, class _U2>
 128   _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
 129   __compressed_pair(_U1&& __t1, _U2&& __t2)
 130       : _Base1(_VSTD::forward<_U1>(__t1)), _Base2(_VSTD::forward<_U2>(__t2)) {}
 131
 132 #ifndef _LIBCPP_CXX03_LANG
 133   template <class... _Args1, class... _Args2>
 134   _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
 135   __compressed_pair(piecewise_construct_t __pc, tuple<_Args1...> __first_args,
 136                     tuple<_Args2...> __second_args)
 137       : _Base1(__pc, _VSTD::move(__first_args),
 138                typename __make_tuple_indices<sizeof...(_Args1)>::type()),
 139         _Base2(__pc, _VSTD::move(__second_args),
 140                typename __make_tuple_indices<sizeof...(_Args2)>::type()) {}
 141 #endif
 142
 143   _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11 typename _Base1::reference first() _NOEXCEPT {
 144     return static_cast<_Base1&>(*this).__get();
 145   }
 146
 147   _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR typename _Base1::const_reference first() const _NOEXCEPT {
 148     return static_cast<_Base1 const&>(*this).__get();
 149   }
 150
 151   _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11 typename _Base2::reference second() _NOEXCEPT {
 152     return static_cast<_Base2&>(*this).__get();
 153   }
 154
 155   _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR typename _Base2::const_reference second() const _NOEXCEPT {
 156     return static_cast<_Base2 const&>(*this).__get();
 157   }
 158
 159   _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
 160   static _Base1* __get_first_base(__compressed_pair* __pair) _NOEXCEPT {
 161     return static_cast<_Base1*>(__pair);
 162   }
 163   _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
 164   static _Base2* __get_second_base(__compressed_pair* __pair) _NOEXCEPT {
 165     return static_cast<_Base2*>(__pair);
 166   }
 167
 168   _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11 void swap(__compressed_pair& __x)
 169       _NOEXCEPT_(__is_nothrow_swappable<_T1>::value && __is_nothrow_swappable<_T2>::value) {
 170     using _VSTD::swap;
 171     swap(first(), __x.first());
 172     swap(second(), __x.second());
 173   }
 174 };
 175
 176 template <class _T1, class _T2>
 177 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX11
 178 void swap(__compressed_pair<_T1, _T2>& __x, __compressed_pair<_T1, _T2>& __y)
 179     _NOEXCEPT_(__is_nothrow_swappable<_T1>::value && __is_nothrow_swappable<_T2>::value) {
 180   __x.swap(__y);
 181 }
 182
 183 _LIBCPP_END_NAMESPACE_STD
 184
 185 #endif // _LIBCPP___MEMORY_COMPRESSED_PAIR_H