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 <__fwd/get.h>
  15 #include <__fwd/tuple.h>
  16 #include <__tuple/tuple_indices.h>
  17 #include <__type_traits/decay.h>
  18 #include <__type_traits/dependent_type.h>
  19 #include <__type_traits/enable_if.h>
  20 #include <__type_traits/is_default_constructible.h>
  21 #include <__type_traits/is_empty.h>
  22 #include <__type_traits/is_final.h>
  23 #include <__type_traits/is_same.h>
  24 #include <__type_traits/is_swappable.h>
  25 #include <__utility/forward.h>
  26 #include <__utility/move.h>
  27 #include <__utility/piecewise_construct.h>
  28 #include <cstddef>
  29
  30 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  31 #  pragma GCC system_header
  32 #endif
  33
  34 _LIBCPP_PUSH_MACROS
  35 #include <__undef_macros>
  36
  37 _LIBCPP_BEGIN_NAMESPACE_STD
  38
  39 // Tag used to default initialize one or both of the pair's elements.
  40 struct __default_init_tag {};
  41 struct __value_init_tag {};
  42
  43 template <class _Tp, int _Idx, bool _CanBeEmptyBase = is_empty<_Tp>::value && !__libcpp_is_final<_Tp>::value>
  44 struct __compressed_pair_elem {
  45   using _ParamT = _Tp;
  46   using reference = _Tp&;
  47   using const_reference = const _Tp&;
  48
  49   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR explicit __compressed_pair_elem(__default_init_tag) {}
  50   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR explicit __compressed_pair_elem(__value_init_tag) : __value_() {}
  51
  52   template <class _Up, class = __enable_if_t<!is_same<__compressed_pair_elem, __decay_t<_Up> >::value> >
  53   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR
  54   explicit __compressed_pair_elem(_Up&& __u) : __value_(std::forward<_Up>(__u)) {}
  55
  56 #ifndef _LIBCPP_CXX03_LANG
  57   template <class... _Args, size_t... _Indices>
  58   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17
  59   explicit __compressed_pair_elem(piecewise_construct_t, tuple<_Args...> __args, __tuple_indices<_Indices...>)
  60       : __value_(std::forward<_Args>(std::get<_Indices>(__args))...) {}
  61 #endif
  62
  63   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 reference __get() _NOEXCEPT { return __value_; }
  64   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR const_reference __get() const _NOEXCEPT { return __value_; }
  65
  66 private:
  67   _Tp __value_;
  68 };
  69
  70 template <class _Tp, int _Idx>
  71 struct __compressed_pair_elem<_Tp, _Idx, true> : private _Tp {
  72   using _ParamT = _Tp;
  73   using reference = _Tp&;
  74   using const_reference = const _Tp&;
  75   using __value_type = _Tp;
  76
  77   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR explicit __compressed_pair_elem() = default;
  78   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR explicit __compressed_pair_elem(__default_init_tag) {}
  79   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR explicit __compressed_pair_elem(__value_init_tag) : __value_type() {}
  80
  81   template <class _Up, class = __enable_if_t<!is_same<__compressed_pair_elem, __decay_t<_Up> >::value> >
  82   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR
  83   explicit __compressed_pair_elem(_Up&& __u) : __value_type(std::forward<_Up>(__u)) {}
  84
  85 #ifndef _LIBCPP_CXX03_LANG
  86   template <class... _Args, size_t... _Indices>
  87   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17
  88   __compressed_pair_elem(piecewise_construct_t, tuple<_Args...> __args, __tuple_indices<_Indices...>)
  89       : __value_type(std::forward<_Args>(std::get<_Indices>(__args))...) {}
  90 #endif
  91
  92   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 reference __get() _NOEXCEPT { return *this; }
  93   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR const_reference __get() const _NOEXCEPT { return *this; }
  94 };
  95
  96 template <class _T1, class _T2>
  97 class __compressed_pair : private __compressed_pair_elem<_T1, 0>,
  98                           private __compressed_pair_elem<_T2, 1> {
  99 public:
 100   // NOTE: This static assert should never fire because __compressed_pair
 101   // is *almost never* used in a scenario where it's possible for T1 == T2.
 102   // (The exception is std::function where it is possible that the function
 103   //  object and the allocator have the same type).
 104   static_assert((!is_same<_T1, _T2>::value),
 105     "__compressed_pair cannot be instantiated when T1 and T2 are the same type; "
 106     "The current implementation is NOT ABI-compatible with the previous implementation for this configuration");
 107
 108   using _Base1 _LIBCPP_NODEBUG = __compressed_pair_elem<_T1, 0>;
 109   using _Base2 _LIBCPP_NODEBUG = __compressed_pair_elem<_T2, 1>;
 110
 111   template <bool _Dummy = true,
 112     class = __enable_if_t<
 113         __dependent_type<is_default_constructible<_T1>, _Dummy>::value &&
 114         __dependent_type<is_default_constructible<_T2>, _Dummy>::value
 115     >
 116   >
 117   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR
 118   explicit __compressed_pair() : _Base1(__value_init_tag()), _Base2(__value_init_tag()) {}
 119
 120   template <class _U1, class _U2>
 121   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR
 122   explicit __compressed_pair(_U1&& __t1, _U2&& __t2) : _Base1(std::forward<_U1>(__t1)), _Base2(std::forward<_U2>(__t2)) {}
 123
 124 #ifndef _LIBCPP_CXX03_LANG
 125   template <class... _Args1, class... _Args2>
 126   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17
 127   explicit __compressed_pair(piecewise_construct_t __pc, tuple<_Args1...> __first_args,
 128                              tuple<_Args2...> __second_args)
 129       : _Base1(__pc, std::move(__first_args), typename __make_tuple_indices<sizeof...(_Args1)>::type()),
 130         _Base2(__pc, std::move(__second_args), typename __make_tuple_indices<sizeof...(_Args2)>::type()) {}
 131 #endif
 132
 133   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14
 134   typename _Base1::reference first() _NOEXCEPT {
 135     return static_cast<_Base1&>(*this).__get();
 136   }
 137
 138   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR
 139   typename _Base1::const_reference first() const _NOEXCEPT {
 140     return static_cast<_Base1 const&>(*this).__get();
 141   }
 142
 143   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14
 144   typename _Base2::reference second() _NOEXCEPT {
 145     return static_cast<_Base2&>(*this).__get();
 146   }
 147
 148   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR
 149   typename _Base2::const_reference second() const _NOEXCEPT {
 150     return static_cast<_Base2 const&>(*this).__get();
 151   }
 152
 153   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR static
 154   _Base1* __get_first_base(__compressed_pair* __pair) _NOEXCEPT {
 155     return static_cast<_Base1*>(__pair);
 156   }
 157   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR static
 158   _Base2* __get_second_base(__compressed_pair* __pair) _NOEXCEPT {
 159     return static_cast<_Base2*>(__pair);
 160   }
 161
 162   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14
 163   void swap(__compressed_pair& __x)
 164       _NOEXCEPT_(__is_nothrow_swappable<_T1>::value && __is_nothrow_swappable<_T2>::value) {
 165     using std::swap;
 166     swap(first(), __x.first());
 167     swap(second(), __x.second());
 168   }
 169 };
 170
 171 template <class _T1, class _T2>
 172 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14
 173 void swap(__compressed_pair<_T1, _T2>& __x, __compressed_pair<_T1, _T2>& __y)
 174     _NOEXCEPT_(__is_nothrow_swappable<_T1>::value && __is_nothrow_swappable<_T2>::value) {
 175   __x.swap(__y);
 176 }
 177
 178 _LIBCPP_END_NAMESPACE_STD
 179
 180 _LIBCPP_POP_MACROS
 181
 182 #endif // _LIBCPP___MEMORY_COMPRESSED_PAIR_H