libcxx/include/__memory/compressed_pair.h

// -*- 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_COMPRESSED_PAIR_H
#define _LIBCPP___MEMORY_COMPRESSED_PAIR_H

#include <__config>
#include <__utility/forward.h>
#include <tuple> // needed in c++03 for some constructors
#include <type_traits>
#include <utility>

#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
#pragma GCC system_header
#endif

_LIBCPP_BEGIN_NAMESPACE_STD

// Tag used to default initialize one or both of the pair's elements.
struct __default_init_tag {};
struct __value_init_tag {};

template <class _Tp, int _Idx,
          bool _CanBeEmptyBase =
              is_empty<_Tp>::value && !__libcpp_is_final<_Tp>::value>
struct __compressed_pair_elem {
  typedef _Tp _ParamT;
  typedef _Tp& reference;
  typedef const _Tp& const_reference;

  _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
  __compressed_pair_elem(__default_init_tag) {}
  _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
  __compressed_pair_elem(__value_init_tag) : __value_() {}

  template <class _Up, class = typename enable_if<
      !is_same<__compressed_pair_elem, typename decay<_Up>::type>::value
  >::type>
  _LIBCPP_INLINE_VISIBILITY
  _LIBCPP_CONSTEXPR explicit
  __compressed_pair_elem(_Up&& __u)
      : __value_(_VSTD::forward<_Up>(__u))
    {
    }


#ifndef _LIBCPP_CXX03_LANG
  template <class... _Args, size_t... _Indexes>
  _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
  __compressed_pair_elem(piecewise_construct_t, tuple<_Args...> __args,
                         __tuple_indices<_Indexes...>)
      : __value_(_VSTD::forward<_Args>(_VSTD::get<_Indexes>(__args))...) {}
#endif


  _LIBCPP_INLINE_VISIBILITY reference __get() _NOEXCEPT { return __value_; }
  _LIBCPP_INLINE_VISIBILITY
  const_reference __get() const _NOEXCEPT { return __value_; }

private:
  _Tp __value_;
};

template <class _Tp, int _Idx>
struct __compressed_pair_elem<_Tp, _Idx, true> : private _Tp {
  typedef _Tp _ParamT;
  typedef _Tp& reference;
  typedef const _Tp& const_reference;
  typedef _Tp __value_type;

  _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR __compressed_pair_elem() = default;
  _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
  __compressed_pair_elem(__default_init_tag) {}
  _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
  __compressed_pair_elem(__value_init_tag) : __value_type() {}

  template <class _Up, class = typename enable_if<
        !is_same<__compressed_pair_elem, typename decay<_Up>::type>::value
  >::type>
  _LIBCPP_INLINE_VISIBILITY
  _LIBCPP_CONSTEXPR explicit
  __compressed_pair_elem(_Up&& __u)
      : __value_type(_VSTD::forward<_Up>(__u))
  {}

#ifndef _LIBCPP_CXX03_LANG
  template <class... _Args, size_t... _Indexes>
  _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
  __compressed_pair_elem(piecewise_construct_t, tuple<_Args...> __args,
                         __tuple_indices<_Indexes...>)
      : __value_type(_VSTD::forward<_Args>(_VSTD::get<_Indexes>(__args))...) {}
#endif

  _LIBCPP_INLINE_VISIBILITY reference __get() _NOEXCEPT { return *this; }
  _LIBCPP_INLINE_VISIBILITY
  const_reference __get() const _NOEXCEPT { return *this; }
};

template <class _T1, class _T2>
class __compressed_pair : private __compressed_pair_elem<_T1, 0>,
                          private __compressed_pair_elem<_T2, 1> {
public:
  // NOTE: This static assert should never fire because __compressed_pair
  // is *almost never* used in a scenario where it's possible for T1 == T2.
  // (The exception is std::function where it is possible that the function
  //  object and the allocator have the same type).
  static_assert((!is_same<_T1, _T2>::value),
    "__compressed_pair cannot be instantiated when T1 and T2 are the same type; "
    "The current implementation is NOT ABI-compatible with the previous "
    "implementation for this configuration");

    typedef _LIBCPP_NODEBUG __compressed_pair_elem<_T1, 0> _Base1;
    typedef _LIBCPP_NODEBUG __compressed_pair_elem<_T2, 1> _Base2;

    template <bool _Dummy = true,
      class = typename enable_if<
          __dependent_type<is_default_constructible<_T1>, _Dummy>::value &&
          __dependent_type<is_default_constructible<_T2>, _Dummy>::value
      >::type
  >
  _LIBCPP_INLINE_VISIBILITY
  _LIBCPP_CONSTEXPR __compressed_pair() : _Base1(__value_init_tag()), _Base2(__value_init_tag()) {}

  template <class _U1, class _U2>
  _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
  __compressed_pair(_U1&& __t1, _U2&& __t2)
      : _Base1(_VSTD::forward<_U1>(__t1)), _Base2(_VSTD::forward<_U2>(__t2)) {}

#ifndef _LIBCPP_CXX03_LANG
  template <class... _Args1, class... _Args2>
  _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX14
  __compressed_pair(piecewise_construct_t __pc, tuple<_Args1...> __first_args,
                    tuple<_Args2...> __second_args)
      : _Base1(__pc, _VSTD::move(__first_args),
               typename __make_tuple_indices<sizeof...(_Args1)>::type()),
        _Base2(__pc, _VSTD::move(__second_args),
               typename __make_tuple_indices<sizeof...(_Args2)>::type()) {}
#endif

  _LIBCPP_INLINE_VISIBILITY
  typename _Base1::reference first() _NOEXCEPT {
    return static_cast<_Base1&>(*this).__get();
  }

  _LIBCPP_INLINE_VISIBILITY
  typename _Base1::const_reference first() const _NOEXCEPT {
    return static_cast<_Base1 const&>(*this).__get();
  }

  _LIBCPP_INLINE_VISIBILITY
  typename _Base2::reference second() _NOEXCEPT {
    return static_cast<_Base2&>(*this).__get();
  }

  _LIBCPP_INLINE_VISIBILITY
  typename _Base2::const_reference second() const _NOEXCEPT {
    return static_cast<_Base2 const&>(*this).__get();
  }

  _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
  static _Base1* __get_first_base(__compressed_pair* __pair) _NOEXCEPT {
    return static_cast<_Base1*>(__pair);
  }
  _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
  static _Base2* __get_second_base(__compressed_pair* __pair) _NOEXCEPT {
    return static_cast<_Base2*>(__pair);
  }

  _LIBCPP_INLINE_VISIBILITY
  void swap(__compressed_pair& __x)
    _NOEXCEPT_(__is_nothrow_swappable<_T1>::value &&
               __is_nothrow_swappable<_T2>::value)
  {
    using _VSTD::swap;
    swap(first(), __x.first());
    swap(second(), __x.second());
  }
};

template <class _T1, class _T2>
inline _LIBCPP_INLINE_VISIBILITY
void swap(__compressed_pair<_T1, _T2>& __x, __compressed_pair<_T1, _T2>& __y)
    _NOEXCEPT_(__is_nothrow_swappable<_T1>::value &&
               __is_nothrow_swappable<_T2>::value) {
  __x.swap(__y);
}

_LIBCPP_END_NAMESPACE_STD

#endif // _LIBCPP___MEMORY_COMPRESSED_PAIR_H