boost_unordered/include/boost/unordered/detail/implementation.hpp

// Copyright (C) 2003-2004 Jeremy B. Maitin-Shepard.
// Copyright (C) 2005-2016 Daniel James
// Copyright (C) 2022 Joaquin M Lopez Munoz.
// Copyright (C) 2022 Christian Mazakas
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)

#ifndef BOOST_UNORDERED_DETAIL_IMPLEMENTATION_HPP
#define BOOST_UNORDERED_DETAIL_IMPLEMENTATION_HPP

#include <boost/config.hpp>
#if defined(BOOST_HAS_PRAGMA_ONCE)
#pragma once
#endif

#include <boost/assert.hpp>
#include <boost/core/allocator_traits.hpp>
#include <boost/core/bit.hpp>
#include <boost/core/no_exceptions_support.hpp>
#include <boost/core/pointer_traits.hpp>
#include <boost/limits.hpp>
#include <boost/move/move.hpp>
#include <boost/preprocessor/arithmetic/inc.hpp>
#include <boost/preprocessor/cat.hpp>
#include <boost/preprocessor/repetition/enum.hpp>
#include <boost/preprocessor/repetition/enum_binary_params.hpp>
#include <boost/preprocessor/repetition/enum_params.hpp>
#include <boost/preprocessor/repetition/repeat_from_to.hpp>
#include <boost/preprocessor/seq/enum.hpp>
#include <boost/preprocessor/seq/size.hpp>
#include <boost/swap.hpp>
#include <boost/throw_exception.hpp>
#include <boost/tuple/tuple.hpp>
#include <boost/type_traits/add_lvalue_reference.hpp>
#include <boost/type_traits/aligned_storage.hpp>
#include <boost/type_traits/alignment_of.hpp>
#include <boost/type_traits/integral_constant.hpp>
#include <boost/type_traits/is_base_of.hpp>
#include <boost/type_traits/is_class.hpp>
#include <boost/type_traits/is_convertible.hpp>
#include <boost/type_traits/is_empty.hpp>
#include <boost/type_traits/is_nothrow_move_assignable.hpp>
#include <boost/type_traits/is_nothrow_move_constructible.hpp>
#include <boost/type_traits/is_nothrow_swappable.hpp>
#include <boost/type_traits/is_same.hpp>
#include <boost/type_traits/make_void.hpp>
#include <boost/type_traits/remove_const.hpp>
#include <boost/unordered/detail/fca.hpp>
#include <boost/unordered/detail/fwd.hpp>
#include <boost/utility/addressof.hpp>
#include <boost/utility/enable_if.hpp>
#include <cmath>
#include <iterator>
#include <stdexcept>
#include <utility>

#if !defined(BOOST_NO_CXX11_HDR_TYPE_TRAITS)
#include <type_traits>
#endif

////////////////////////////////////////////////////////////////////////////////
// Configuration
//
// Unless documented elsewhere these configuration macros should be considered
// an implementation detail, I'll try not to break them, but you never know.

// Use Sun C++ workarounds
// I'm not sure which versions of the compiler require these workarounds, so
// I'm just using them of everything older than the current test compilers
// (as of May 2017).

#if !defined(BOOST_UNORDERED_SUN_WORKAROUNDS1)
#if BOOST_COMP_SUNPRO && BOOST_COMP_SUNPRO < BOOST_VERSION_NUMBER(5, 20, 0)
#define BOOST_UNORDERED_SUN_WORKAROUNDS1 1
#else
#define BOOST_UNORDERED_SUN_WORKAROUNDS1 0
#endif
#endif

// BOOST_UNORDERED_EMPLACE_LIMIT = The maximum number of parameters in
// emplace (not including things like hints). Don't set it to a lower value, as
// that might break something.

#if !defined BOOST_UNORDERED_EMPLACE_LIMIT
#define BOOST_UNORDERED_EMPLACE_LIMIT 10
#endif

// BOOST_UNORDERED_TUPLE_ARGS
//
// Maximum number of std::tuple members to support, or 0 if std::tuple
// isn't avaiable. More are supported when full C++11 is used.

// Already defined, so do nothing
#if defined(BOOST_UNORDERED_TUPLE_ARGS)

// Assume if we have C++11 tuple it's properly variadic,
// and just use a max number of 10 arguments.
#elif !defined(BOOST_NO_CXX11_HDR_TUPLE)
#define BOOST_UNORDERED_TUPLE_ARGS 10

// Visual C++ has a decent enough tuple for piecewise construction,
// so use that if available, using _VARIADIC_MAX for the maximum
// number of parameters. Note that this comes after the check
// for a full C++11 tuple.
#elif defined(BOOST_MSVC)
#if !BOOST_UNORDERED_HAVE_PIECEWISE_CONSTRUCT
#define BOOST_UNORDERED_TUPLE_ARGS 0
#elif defined(_VARIADIC_MAX)
#define BOOST_UNORDERED_TUPLE_ARGS _VARIADIC_MAX
#else
#define BOOST_UNORDERED_TUPLE_ARGS 5
#endif

// Assume that we don't have std::tuple
#else
#define BOOST_UNORDERED_TUPLE_ARGS 0
#endif

#if BOOST_UNORDERED_TUPLE_ARGS
#include <tuple>
#endif

// BOOST_UNORDERED_CXX11_CONSTRUCTION
//
// Use C++11 construction, requires variadic arguments, good construct support
// in allocator_traits and piecewise construction of std::pair
// Otherwise allocators aren't used for construction/destruction

#if BOOST_UNORDERED_HAVE_PIECEWISE_CONSTRUCT &&                                \
  !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES) && BOOST_UNORDERED_TUPLE_ARGS
#if BOOST_COMP_SUNPRO && BOOST_LIB_STD_GNU
// Sun C++ std::pair piecewise construction doesn't seem to be exception safe.
// (At least for Sun C++ 12.5 using libstdc++).
#define BOOST_UNORDERED_CXX11_CONSTRUCTION 0
#elif BOOST_COMP_GNUC && BOOST_COMP_GNUC < BOOST_VERSION_NUMBER(4, 7, 0)
// Piecewise construction in GCC 4.6 doesn't work for uncopyable types.
#define BOOST_UNORDERED_CXX11_CONSTRUCTION 0
#elif !defined(BOOST_NO_CXX11_ALLOCATOR)
#define BOOST_UNORDERED_CXX11_CONSTRUCTION 1
#endif
#endif

#if !defined(BOOST_UNORDERED_CXX11_CONSTRUCTION)
#define BOOST_UNORDERED_CXX11_CONSTRUCTION 0
#endif

#if BOOST_UNORDERED_CXX11_CONSTRUCTION
#include <boost/mp11/list.hpp>
#include <boost/mp11/algorithm.hpp>
#endif

// BOOST_UNORDERED_SUPPRESS_DEPRECATED
//
// Define to stop deprecation attributes

#if defined(BOOST_UNORDERED_SUPPRESS_DEPRECATED)
#define BOOST_UNORDERED_DEPRECATED(msg)
#endif

// BOOST_UNORDERED_DEPRECATED
//
// Wrapper around various depreaction attributes.

#if defined(__has_cpp_attribute) &&                                            \
  (!defined(__cplusplus) || __cplusplus >= 201402)
#if __has_cpp_attribute(deprecated) && !defined(BOOST_UNORDERED_DEPRECATED)
#define BOOST_UNORDERED_DEPRECATED(msg) [[deprecated(msg)]]
#endif
#endif

#if !defined(BOOST_UNORDERED_DEPRECATED)
#if defined(__GNUC__) && __GNUC__ >= 4
#define BOOST_UNORDERED_DEPRECATED(msg) __attribute__((deprecated))
#elif defined(_MSC_VER) && _MSC_VER >= 1400
#define BOOST_UNORDERED_DEPRECATED(msg) __declspec(deprecated(msg))
#elif defined(_MSC_VER) && _MSC_VER >= 1310
#define BOOST_UNORDERED_DEPRECATED(msg) __declspec(deprecated)
#else
#define BOOST_UNORDERED_DEPRECATED(msg)
#endif
#endif

// BOOST_UNORDERED_TEMPLATE_DEDUCTION_GUIDES

#if !defined(BOOST_UNORDERED_TEMPLATE_DEDUCTION_GUIDES)
#if BOOST_COMP_CLANG && __cplusplus >= 201703
#define BOOST_UNORDERED_TEMPLATE_DEDUCTION_GUIDES 1
#endif
#endif

#if !defined(BOOST_UNORDERED_TEMPLATE_DEDUCTION_GUIDES)
#define BOOST_UNORDERED_TEMPLATE_DEDUCTION_GUIDES 0
#endif

namespace boost {
  namespace unordered {
    namespace detail {

      template <typename Types> struct table;

      static const float minimum_max_load_factor = 1e-3f;
      static const std::size_t default_bucket_count = 11;

      struct move_tag
      {
      };

      struct empty_emplace
      {
      };

      struct no_key
      {
        no_key() {}
        template <class T> no_key(T const&) {}
      };

      namespace func {
        template <class T> inline void ignore_unused_variable_warning(T const&)
        {
        }
      }

      //////////////////////////////////////////////////////////////////////////
      // iterator SFINAE

      template <typename I>
      struct is_forward : boost::is_base_of<std::forward_iterator_tag,
                            typename std::iterator_traits<I>::iterator_category>
      {
      };

      template <typename I, typename ReturnType>
      struct enable_if_forward
        : boost::enable_if_c<boost::unordered::detail::is_forward<I>::value,
            ReturnType>
      {
      };

      template <typename I, typename ReturnType>
      struct disable_if_forward
        : boost::disable_if_c<boost::unordered::detail::is_forward<I>::value,
            ReturnType>
      {
      };
    }
  }
}

namespace boost {
  namespace unordered {
    namespace detail {
      //////////////////////////////////////////////////////////////////////////
      // insert_size/initial_size

      template <class I>
      inline typename boost::unordered::detail::enable_if_forward<I,
        std::size_t>::type
      insert_size(I i, I j)
      {
        return static_cast<std::size_t>(std::distance(i, j));
      }

      template <class I>
      inline typename boost::unordered::detail::disable_if_forward<I,
        std::size_t>::type insert_size(I, I)
      {
        return 1;
      }

      template <class I>
      inline std::size_t initial_size(I i, I j,
        std::size_t num_buckets =
          boost::unordered::detail::default_bucket_count)
      {
        return (std::max)(
          boost::unordered::detail::insert_size(i, j), num_buckets);
      }

      //////////////////////////////////////////////////////////////////////////
      // compressed

      template <typename T, int Index>
      struct compressed_base : boost::empty_value<T>
      {
        compressed_base(T const& x) : empty_value<T>(boost::empty_init_t(), x)
        {
        }
        compressed_base(T& x, move_tag)
            : empty_value<T>(boost::empty_init_t(), boost::move(x))
        {
        }

        T& get() { return empty_value<T>::get(); }
        T const& get() const { return empty_value<T>::get(); }
      };

      template <typename T, int Index>
      struct generate_base : boost::unordered::detail::compressed_base<T, Index>
      {
        typedef compressed_base<T, Index> type;

        generate_base() : type() {}
      };

      template <typename T1, typename T2>
      struct compressed
        : private boost::unordered::detail::generate_base<T1, 1>::type,
          private boost::unordered::detail::generate_base<T2, 2>::type
      {
        typedef typename generate_base<T1, 1>::type base1;
        typedef typename generate_base<T2, 2>::type base2;

        typedef T1 first_type;
        typedef T2 second_type;

        first_type& first() { return static_cast<base1*>(this)->get(); }

        first_type const& first() const
        {
          return static_cast<base1 const*>(this)->get();
        }

        second_type& second() { return static_cast<base2*>(this)->get(); }

        second_type const& second() const
        {
          return static_cast<base2 const*>(this)->get();
        }

        template <typename First, typename Second>
        compressed(First const& x1, Second const& x2) : base1(x1), base2(x2)
        {
        }

        compressed(compressed const& x) : base1(x.first()), base2(x.second()) {}

        compressed(compressed& x, move_tag m)
            : base1(x.first(), m), base2(x.second(), m)
        {
        }

        void assign(compressed const& x)
        {
          first() = x.first();
          second() = x.second();
        }

        void move_assign(compressed& x)
        {
          first() = boost::move(x.first());
          second() = boost::move(x.second());
        }

        void swap(compressed& x)
        {
          boost::swap(first(), x.first());
          boost::swap(second(), x.second());
        }

      private:
        // Prevent assignment just to make use of assign or
        // move_assign explicit.
        compressed& operator=(compressed const&);
      };

      //////////////////////////////////////////////////////////////////////////
      // pair_traits
      //
      // Used to get the types from a pair without instantiating it.

      template <typename Pair> struct pair_traits
      {
        typedef typename Pair::first_type first_type;
        typedef typename Pair::second_type second_type;
      };

      template <typename T1, typename T2> struct pair_traits<std::pair<T1, T2> >
      {
        typedef T1 first_type;
        typedef T2 second_type;
      };

#if defined(BOOST_MSVC)
#pragma warning(push)
#pragma warning(disable : 4512) // assignment operator could not be generated.
#pragma warning(disable : 4345) // behavior change: an object of POD type
// constructed with an initializer of the form ()
// will be default-initialized.
#endif

      //////////////////////////////////////////////////////////////////////////
      // Bits and pieces for implementing traits

      template <typename T>
      typename boost::add_lvalue_reference<T>::type make();
      struct choice9
      {
        typedef char (&type)[9];
      };
      struct choice8 : choice9
      {
        typedef char (&type)[8];
      };
      struct choice7 : choice8
      {
        typedef char (&type)[7];
      };
      struct choice6 : choice7
      {
        typedef char (&type)[6];
      };
      struct choice5 : choice6
      {
        typedef char (&type)[5];
      };
      struct choice4 : choice5
      {
        typedef char (&type)[4];
      };
      struct choice3 : choice4
      {
        typedef char (&type)[3];
      };
      struct choice2 : choice3
      {
        typedef char (&type)[2];
      };
      struct choice1 : choice2
      {
        typedef char (&type)[1];
      };
      choice1 choose();

      typedef choice1::type yes_type;
      typedef choice2::type no_type;

      struct private_type
      {
        private_type const& operator,(int) const;
      };

      template <typename T> no_type is_private_type(T const&);
      yes_type is_private_type(private_type const&);

      struct convert_from_anything
      {
        template <typename T> convert_from_anything(T const&);
      };
    }
  }
}

////////////////////////////////////////////////////////////////////////////
// emplace_args
//
// Either forwarding variadic arguments, or storing the arguments in
// emplace_args##n

#if !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES)

#define BOOST_UNORDERED_EMPLACE_TEMPLATE typename... Args
#define BOOST_UNORDERED_EMPLACE_ARGS BOOST_FWD_REF(Args)... args
#define BOOST_UNORDERED_EMPLACE_FORWARD boost::forward<Args>(args)...

#else

#define BOOST_UNORDERED_EMPLACE_TEMPLATE typename Args
#define BOOST_UNORDERED_EMPLACE_ARGS Args const& args
#define BOOST_UNORDERED_EMPLACE_FORWARD args

#if defined(BOOST_NO_CXX11_RVALUE_REFERENCES)

#define BOOST_UNORDERED_EARGS_MEMBER(z, n, _)                                  \
  typedef BOOST_FWD_REF(BOOST_PP_CAT(A, n)) BOOST_PP_CAT(Arg, n);              \
  BOOST_PP_CAT(Arg, n) BOOST_PP_CAT(a, n);

#else

#define BOOST_UNORDERED_EARGS_MEMBER(z, n, _)                                  \
  typedef typename boost::add_lvalue_reference<BOOST_PP_CAT(A, n)>::type       \
    BOOST_PP_CAT(Arg, n);                                                      \
  BOOST_PP_CAT(Arg, n) BOOST_PP_CAT(a, n);

#endif

#define BOOST_UNORDERED_FWD_PARAM(z, n, a)                                     \
  BOOST_FWD_REF(BOOST_PP_CAT(A, n)) BOOST_PP_CAT(a, n)

#define BOOST_UNORDERED_CALL_FORWARD(z, i, a)                                  \
  boost::forward<BOOST_PP_CAT(A, i)>(BOOST_PP_CAT(a, i))

#define BOOST_UNORDERED_EARGS_INIT(z, n, _)                                    \
  BOOST_PP_CAT(a, n)(BOOST_PP_CAT(b, n))

#define BOOST_UNORDERED_EARGS(z, n, _)                                         \
  template <BOOST_PP_ENUM_PARAMS_Z(z, n, typename A)>                          \
  struct BOOST_PP_CAT(emplace_args, n)                                         \
  {                                                                            \
    BOOST_PP_REPEAT_##z(n, BOOST_UNORDERED_EARGS_MEMBER, _) BOOST_PP_CAT(      \
      emplace_args, n)(BOOST_PP_ENUM_BINARY_PARAMS_Z(z, n, Arg, b))            \
        : BOOST_PP_ENUM_##z(n, BOOST_UNORDERED_EARGS_INIT, _)                  \
    {                                                                          \
    }                                                                          \
  };                                                                           \
                                                                               \
  template <BOOST_PP_ENUM_PARAMS_Z(z, n, typename A)>                          \
  inline BOOST_PP_CAT(emplace_args, n)<BOOST_PP_ENUM_PARAMS_Z(z, n, A)>        \
    create_emplace_args(BOOST_PP_ENUM_##z(n, BOOST_UNORDERED_FWD_PARAM, b))    \
  {                                                                            \
    BOOST_PP_CAT(emplace_args, n)<BOOST_PP_ENUM_PARAMS_Z(z, n, A)> e(          \
      BOOST_PP_ENUM_PARAMS_Z(z, n, b));                                        \
    return e;                                                                  \
  }

namespace boost {
  namespace unordered {
    namespace detail {
      template <typename A0> struct emplace_args1
      {
        BOOST_UNORDERED_EARGS_MEMBER(1, 0, _)

        explicit emplace_args1(Arg0 b0) : a0(b0) {}
      };

      template <typename A0>
      inline emplace_args1<A0> create_emplace_args(BOOST_FWD_REF(A0) b0)
      {
        emplace_args1<A0> e(b0);
        return e;
      }

      template <typename A0, typename A1> struct emplace_args2
      {
        BOOST_UNORDERED_EARGS_MEMBER(1, 0, _)
        BOOST_UNORDERED_EARGS_MEMBER(1, 1, _)

        emplace_args2(Arg0 b0, Arg1 b1) : a0(b0), a1(b1) {}
      };

      template <typename A0, typename A1>
      inline emplace_args2<A0, A1> create_emplace_args(
        BOOST_FWD_REF(A0) b0, BOOST_FWD_REF(A1) b1)
      {
        emplace_args2<A0, A1> e(b0, b1);
        return e;
      }

      template <typename A0, typename A1, typename A2> struct emplace_args3
      {
        BOOST_UNORDERED_EARGS_MEMBER(1, 0, _)
        BOOST_UNORDERED_EARGS_MEMBER(1, 1, _)
        BOOST_UNORDERED_EARGS_MEMBER(1, 2, _)

        emplace_args3(Arg0 b0, Arg1 b1, Arg2 b2) : a0(b0), a1(b1), a2(b2) {}
      };

      template <typename A0, typename A1, typename A2>
      inline emplace_args3<A0, A1, A2> create_emplace_args(
        BOOST_FWD_REF(A0) b0, BOOST_FWD_REF(A1) b1, BOOST_FWD_REF(A2) b2)
      {
        emplace_args3<A0, A1, A2> e(b0, b1, b2);
        return e;
      }

      BOOST_UNORDERED_EARGS(1, 4, _)
      BOOST_UNORDERED_EARGS(1, 5, _)
      BOOST_UNORDERED_EARGS(1, 6, _)
      BOOST_UNORDERED_EARGS(1, 7, _)
      BOOST_UNORDERED_EARGS(1, 8, _)
      BOOST_UNORDERED_EARGS(1, 9, _)
      BOOST_PP_REPEAT_FROM_TO(10, BOOST_PP_INC(BOOST_UNORDERED_EMPLACE_LIMIT),
        BOOST_UNORDERED_EARGS, _)
    }
  }
}

#undef BOOST_UNORDERED_DEFINE_EMPLACE_ARGS
#undef BOOST_UNORDERED_EARGS_MEMBER
#undef BOOST_UNORDERED_EARGS_INIT

#endif

////////////////////////////////////////////////////////////////////////////////
//
// Some utilities for implementing allocator_traits, but useful elsewhere so
// they're always defined.

namespace boost {
  namespace unordered {
    namespace detail {

////////////////////////////////////////////////////////////////////////////
// Integral_constrant, true_type, false_type
//
// Uses the standard versions if available.

#if !defined(BOOST_NO_CXX11_HDR_TYPE_TRAITS)

      using std::integral_constant;
      using std::true_type;
      using std::false_type;

#else

      template <typename T, T Value> struct integral_constant
      {
        enum
        {
          value = Value
        };
      };

      typedef boost::unordered::detail::integral_constant<bool, true> true_type;
      typedef boost::unordered::detail::integral_constant<bool, false>
        false_type;

#endif

////////////////////////////////////////////////////////////////////////////
// Type checkers used for the transparent member functions added by C++20 and up

      template <class, class = void> struct is_transparent : public false_type
      {
      };

      template <class T>
      struct is_transparent<T,
        typename boost::make_void<typename T::is_transparent>::type>
          : public true_type
      {
      };

      template <class, class A, class B> struct are_transparent
      {
        static bool const value =
          is_transparent<A>::value && is_transparent<B>::value;
      };

      template <class Key, class UnorderedMap> struct transparent_non_iterable
      {
        typedef typename UnorderedMap::hasher hash;
        typedef typename UnorderedMap::key_equal key_equal;
        typedef typename UnorderedMap::iterator iterator;
        typedef typename UnorderedMap::const_iterator const_iterator;

        static bool const value =
          are_transparent<Key, hash, key_equal>::value &&
          !boost::is_convertible<Key, iterator>::value &&
          !boost::is_convertible<Key, const_iterator>::value;
      };

////////////////////////////////////////////////////////////////////////////
// Explicitly call a destructor

#if defined(BOOST_MSVC)
#pragma warning(push)
#pragma warning(disable : 4100) // unreferenced formal parameter
#endif

      namespace func {
        template <class T> inline void destroy(T* x) { x->~T(); }
      }

#if defined(BOOST_MSVC)
#pragma warning(pop)
#endif

      //////////////////////////////////////////////////////////////////////////
      // value_base
      //
      // Space used to store values.

      template <typename ValueType> struct value_base
      {
        typedef ValueType value_type;

        typename boost::aligned_storage<sizeof(value_type),
          boost::alignment_of<value_type>::value>::type data_;

        value_base() : data_() {}

        void* address() { return this; }

        value_type& value() { return *(ValueType*)this; }

        value_type const& value() const { return *(ValueType const*)this; }

        value_type* value_ptr() { return (ValueType*)this; }

        value_type const* value_ptr() const { return (ValueType const*)this; }

      private:
        value_base& operator=(value_base const&);
      };

      //////////////////////////////////////////////////////////////////////////
      // optional
      // TODO: Use std::optional when available.

      template <typename T> class optional
      {
        BOOST_MOVABLE_BUT_NOT_COPYABLE(optional)

        boost::unordered::detail::value_base<T> value_;
        bool has_value_;

        void destroy()
        {
          if (has_value_) {
            boost::unordered::detail::func::destroy(value_.value_ptr());
            has_value_ = false;
          }
        }

        void move(optional<T>& x)
        {
          BOOST_ASSERT(!has_value_ && x.has_value_);
          new (value_.value_ptr()) T(boost::move(x.value_.value()));
          boost::unordered::detail::func::destroy(x.value_.value_ptr());
          has_value_ = true;
          x.has_value_ = false;
        }

      public:
        optional() BOOST_NOEXCEPT : has_value_(false) {}

        optional(BOOST_RV_REF(optional<T>) x) : has_value_(false)
        {
          if (x.has_value_) {
            move(x);
          }
        }

        explicit optional(T const& x) : has_value_(true)
        {
          new (value_.value_ptr()) T(x);
        }

        optional& operator=(BOOST_RV_REF(optional<T>) x)
        {
          destroy();
          if (x.has_value_) {
            move(x);
          }
          return *this;
        }

        ~optional() { destroy(); }

        bool has_value() const { return has_value_; }
        T& operator*() { return value_.value(); }
        T const& operator*() const { return value_.value(); }
        T* operator->() { return value_.value_ptr(); }
        T const* operator->() const { return value_.value_ptr(); }

        bool operator==(optional<T> const& x) const
        {
          return has_value_ ? x.has_value_ && value_.value() == x.value_.value()
                            : !x.has_value_;
        }

        bool operator!=(optional<T> const& x) const { return !((*this) == x); }

        void swap(optional<T>& x)
        {
          if (has_value_ != x.has_value_) {
            if (has_value_) {
              x.move(*this);
            } else {
              move(x);
            }
          } else if (has_value_) {
            boost::swap(value_.value(), x.value_.value());
          }
        }

        friend void swap(optional<T>& x, optional<T>& y) { x.swap(y); }
      };
    }
  }
}

////////////////////////////////////////////////////////////////////////////////
//
// Allocator traits
//

namespace boost {
  namespace unordered {
    namespace detail {

      template <typename Alloc>
      struct allocator_traits : boost::allocator_traits<Alloc>
      {
      };

      template <typename Alloc, typename T>
      struct rebind_wrap : boost::allocator_rebind<Alloc, T>
      {
      };
    }
  }
}

////////////////////////////////////////////////////////////////////////////
// Functions used to construct nodes. Emulates variadic construction,
// piecewise construction etc.

////////////////////////////////////////////////////////////////////////////
// construct_value
//
// Only use allocator_traits::construct, allocator_traits::destroy when full
// C++11 support is available.

#if BOOST_UNORDERED_CXX11_CONSTRUCTION

#elif !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES)

namespace boost {
  namespace unordered {
    namespace detail {
      namespace func {
        template <typename T, typename... Args>
        inline void construct_value(T* address, BOOST_FWD_REF(Args)... args)
        {
          new ((void*)address) T(boost::forward<Args>(args)...);
        }
      }
    }
  }
}

#else

namespace boost {
  namespace unordered {
    namespace detail {
      namespace func {
        template <typename T> inline void construct_value(T* address)
        {
          new ((void*)address) T();
        }

        template <typename T, typename A0>
        inline void construct_value(T* address, BOOST_FWD_REF(A0) a0)
        {
          new ((void*)address) T(boost::forward<A0>(a0));
        }
      }
    }
  }
}

#endif

////////////////////////////////////////////////////////////////////////////
// Construct from tuple
//
// Used to emulate piecewise construction.

#define BOOST_UNORDERED_CONSTRUCT_FROM_TUPLE(z, n, namespace_)                 \
  template <typename Alloc, typename T,                                        \
    BOOST_PP_ENUM_PARAMS_Z(z, n, typename A)>                                  \
  void construct_from_tuple(Alloc&, T* ptr,                                    \
    namespace_::tuple<BOOST_PP_ENUM_PARAMS_Z(z, n, A)> const& x)               \
  {                                                                            \
    new ((void*)ptr)                                                           \
      T(BOOST_PP_ENUM_##z(n, BOOST_UNORDERED_GET_TUPLE_ARG, namespace_));      \
  }

#define BOOST_UNORDERED_GET_TUPLE_ARG(z, n, namespace_) namespace_::get<n>(x)

// construct_from_tuple for boost::tuple
// The workaround for old Sun compilers comes later in the file.

#if !BOOST_UNORDERED_SUN_WORKAROUNDS1

namespace boost {
  namespace unordered {
    namespace detail {
      namespace func {
        template <typename Alloc, typename T>
        void construct_from_tuple(Alloc&, T* ptr, boost::tuple<>)
        {
          new ((void*)ptr) T();
        }

        BOOST_UNORDERED_CONSTRUCT_FROM_TUPLE(1, 1, boost)
        BOOST_UNORDERED_CONSTRUCT_FROM_TUPLE(1, 2, boost)
        BOOST_UNORDERED_CONSTRUCT_FROM_TUPLE(1, 3, boost)
        BOOST_UNORDERED_CONSTRUCT_FROM_TUPLE(1, 4, boost)
        BOOST_UNORDERED_CONSTRUCT_FROM_TUPLE(1, 5, boost)
        BOOST_UNORDERED_CONSTRUCT_FROM_TUPLE(1, 6, boost)
        BOOST_UNORDERED_CONSTRUCT_FROM_TUPLE(1, 7, boost)
        BOOST_UNORDERED_CONSTRUCT_FROM_TUPLE(1, 8, boost)
        BOOST_UNORDERED_CONSTRUCT_FROM_TUPLE(1, 9, boost)
        BOOST_UNORDERED_CONSTRUCT_FROM_TUPLE(1, 10, boost)
      }
    }
  }
}

#endif

// construct_from_tuple for std::tuple

#if !BOOST_UNORDERED_CXX11_CONSTRUCTION && BOOST_UNORDERED_TUPLE_ARGS

namespace boost {
  namespace unordered {
    namespace detail {
      namespace func {
        template <typename Alloc, typename T>
        void construct_from_tuple(Alloc&, T* ptr, std::tuple<>)
        {
          new ((void*)ptr) T();
        }

        BOOST_UNORDERED_CONSTRUCT_FROM_TUPLE(1, 1, std)
        BOOST_UNORDERED_CONSTRUCT_FROM_TUPLE(1, 2, std)
        BOOST_UNORDERED_CONSTRUCT_FROM_TUPLE(1, 3, std)
        BOOST_UNORDERED_CONSTRUCT_FROM_TUPLE(1, 4, std)
        BOOST_UNORDERED_CONSTRUCT_FROM_TUPLE(1, 5, std)

#if BOOST_UNORDERED_TUPLE_ARGS >= 6
        BOOST_PP_REPEAT_FROM_TO(6, BOOST_PP_INC(BOOST_UNORDERED_TUPLE_ARGS),
          BOOST_UNORDERED_CONSTRUCT_FROM_TUPLE, std)
#endif
      }
    }
  }
}

#endif

#undef BOOST_UNORDERED_CONSTRUCT_FROM_TUPLE
#undef BOOST_UNORDERED_GET_TUPLE_ARG

// construct_from_tuple for boost::tuple on old versions of sunpro.
//
// Old versions of Sun C++ had problems with template overloads of
// boost::tuple, so to fix it I added a distinct type for each length to
// the overloads. That means there's no possible ambiguity between the
// different overloads, so that the compiler doesn't get confused

#if BOOST_UNORDERED_SUN_WORKAROUNDS1

#define BOOST_UNORDERED_CONSTRUCT_FROM_TUPLE(z, n, namespace_)                 \
  template <typename Alloc, typename T,                                        \
    BOOST_PP_ENUM_PARAMS_Z(z, n, typename A)>                                  \
  void construct_from_tuple_impl(boost::unordered::detail::func::length<n>,    \
    Alloc&, T* ptr,                                                            \
    namespace_::tuple<BOOST_PP_ENUM_PARAMS_Z(z, n, A)> const& x)               \
  {                                                                            \
    new ((void*)ptr)                                                           \
      T(BOOST_PP_ENUM_##z(n, BOOST_UNORDERED_GET_TUPLE_ARG, namespace_));      \
  }

#define BOOST_UNORDERED_GET_TUPLE_ARG(z, n, namespace_) namespace_::get<n>(x)

namespace boost {
  namespace unordered {
    namespace detail {
      namespace func {
        template <int N> struct length
        {
        };

        template <typename Alloc, typename T>
        void construct_from_tuple_impl(
          boost::unordered::detail::func::length<0>, Alloc&, T* ptr,
          boost::tuple<>)
        {
          new ((void*)ptr) T();
        }

        BOOST_UNORDERED_CONSTRUCT_FROM_TUPLE(1, 1, boost)
        BOOST_UNORDERED_CONSTRUCT_FROM_TUPLE(1, 2, boost)
        BOOST_UNORDERED_CONSTRUCT_FROM_TUPLE(1, 3, boost)
        BOOST_UNORDERED_CONSTRUCT_FROM_TUPLE(1, 4, boost)
        BOOST_UNORDERED_CONSTRUCT_FROM_TUPLE(1, 5, boost)
        BOOST_UNORDERED_CONSTRUCT_FROM_TUPLE(1, 6, boost)
        BOOST_UNORDERED_CONSTRUCT_FROM_TUPLE(1, 7, boost)
        BOOST_UNORDERED_CONSTRUCT_FROM_TUPLE(1, 8, boost)
        BOOST_UNORDERED_CONSTRUCT_FROM_TUPLE(1, 9, boost)
        BOOST_UNORDERED_CONSTRUCT_FROM_TUPLE(1, 10, boost)

        template <typename Alloc, typename T, typename Tuple>
        void construct_from_tuple(Alloc& alloc, T* ptr, Tuple const& x)
        {
          construct_from_tuple_impl(boost::unordered::detail::func::length<
                                      boost::tuples::length<Tuple>::value>(),
            alloc, ptr, x);
        }
      }
    }
  }
}

#undef BOOST_UNORDERED_CONSTRUCT_FROM_TUPLE
#undef BOOST_UNORDERED_GET_TUPLE_ARG

#endif

namespace boost {
  namespace unordered {
    namespace detail {
      namespace func {
        ////////////////////////////////////////////////////////////////////////
        // Trait to check for piecewise construction.

        template <typename A0> struct use_piecewise
        {
          static choice1::type test(
            choice1, boost::unordered::piecewise_construct_t);

          static choice2::type test(choice2, ...);

          enum
          {
            value = sizeof(choice1::type) ==
                    sizeof(test(choose(), boost::unordered::detail::make<A0>()))
          };
        };

#if BOOST_UNORDERED_CXX11_CONSTRUCTION

        ////////////////////////////////////////////////////////////////////////
        // Construct from variadic parameters

        template <typename Alloc, typename T, typename... Args>
        inline void construct_from_args(
          Alloc& alloc, T* address, BOOST_FWD_REF(Args)... args)
        {
          boost::allocator_construct(
            alloc, address, boost::forward<Args>(args)...);
        }

        // For backwards compatibility, implement a special case for
        // piecewise_construct with boost::tuple

        template <typename A0> struct detect_boost_tuple
        {
          template <typename T0, typename T1, typename T2, typename T3,
            typename T4, typename T5, typename T6, typename T7, typename T8,
            typename T9>
          static choice1::type test(choice1,
            boost::tuple<T0, T1, T2, T3, T4, T5, T6, T7, T8, T9> const&);

          static choice2::type test(choice2, ...);

          enum
          {
            value = sizeof(choice1::type) ==
                    sizeof(test(choose(), boost::unordered::detail::make<A0>()))
          };
        };

        // Special case for piecewise_construct

        template <class... Args, std::size_t... Is, class... TupleArgs>
        std::tuple<typename std::add_lvalue_reference<Args>::type...>
        to_std_tuple_impl(boost::mp11::mp_list<Args...>,
          boost::tuple<TupleArgs...>& tuple, boost::mp11::index_sequence<Is...>)
        {
          (void) tuple;
          return std::tuple<typename std::add_lvalue_reference<Args>::type...>(
            boost::get<Is>(tuple)...);
        }

        template <class... Args>
        boost::mp11::index_sequence_for<Args...> make_index_seq(
          boost::mp11::mp_list<Args...>)
        {
          return boost::mp11::index_sequence_for<Args...>{};
        }

        template <class T>
        using add_lvalue_reference_t =
          typename std::add_lvalue_reference<T>::type;

        template <class... Args>
        boost::mp11::mp_transform<add_lvalue_reference_t,
          boost::mp11::mp_remove<std::tuple<Args...>,
            boost::tuples::null_type> >
        to_std_tuple(boost::tuple<Args...>& tuple)
        {
          using list = boost::mp11::mp_remove<boost::mp11::mp_list<Args...>,
            boost::tuples::null_type>;

          return to_std_tuple_impl(list{}, tuple, make_index_seq(list{}));
        }

        template <typename Alloc, typename A, typename B, typename A0,
          typename A1, typename A2>
        inline typename boost::enable_if_c<use_piecewise<A0>::value &&
                                             detect_boost_tuple<A1>::value &&
                                             detect_boost_tuple<A2>::value,
          void>::type
        construct_from_args(Alloc& alloc, std::pair<A, B>* address,
          BOOST_FWD_REF(A0), BOOST_FWD_REF(A1) a1, BOOST_FWD_REF(A2) a2)
        {
          boost::allocator_construct(alloc, address, std::piecewise_construct,
            to_std_tuple(a1), to_std_tuple(a2));
        }

#elif !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES)

        ////////////////////////////////////////////////////////////////////////
        // Construct from variadic parameters

        template <typename Alloc, typename T, typename... Args>
        inline void construct_from_args(
          Alloc&, T* address, BOOST_FWD_REF(Args)... args)
        {
          new ((void*)address) T(boost::forward<Args>(args)...);
        }

        // Special case for piecewise_construct

        template <typename Alloc, typename A, typename B, typename A0,
          typename A1, typename A2>
        inline typename enable_if<use_piecewise<A0>, void>::type
        construct_from_args(Alloc& alloc, std::pair<A, B>* address,
          BOOST_FWD_REF(A0), BOOST_FWD_REF(A1) a1, BOOST_FWD_REF(A2) a2)
        {
          boost::unordered::detail::func::construct_from_tuple(
            alloc, boost::addressof(address->first), boost::forward<A1>(a1));
          BOOST_TRY
          {
            boost::unordered::detail::func::construct_from_tuple(
              alloc, boost::addressof(address->second), boost::forward<A2>(a2));
          }
          BOOST_CATCH(...)
          {
            boost::unordered::detail::func::destroy(
              boost::addressof(address->first));
            BOOST_RETHROW
          }
          BOOST_CATCH_END
        }

#else // BOOST_NO_CXX11_VARIADIC_TEMPLATES

        ////////////////////////////////////////////////////////////////////////
        // Construct from emplace_args

        // Explicitly write out first three overloads for the sake of sane
        // error messages.

        template <typename Alloc, typename T, typename A0>
        inline void construct_from_args(
          Alloc&, T* address, emplace_args1<A0> const& args)
        {
          new ((void*)address) T(boost::forward<A0>(args.a0));
        }

        template <typename Alloc, typename T, typename A0, typename A1>
        inline void construct_from_args(
          Alloc&, T* address, emplace_args2<A0, A1> const& args)
        {
          new ((void*)address)
            T(boost::forward<A0>(args.a0), boost::forward<A1>(args.a1));
        }

        template <typename Alloc, typename T, typename A0, typename A1,
          typename A2>
        inline void construct_from_args(
          Alloc&, T* address, emplace_args3<A0, A1, A2> const& args)
        {
          new ((void*)address) T(boost::forward<A0>(args.a0),
            boost::forward<A1>(args.a1), boost::forward<A2>(args.a2));
        }

// Use a macro for the rest.

#define BOOST_UNORDERED_CONSTRUCT_IMPL(z, num_params, _)                       \
  template <typename Alloc, typename T,                                        \
    BOOST_PP_ENUM_PARAMS_Z(z, num_params, typename A)>                         \
  inline void construct_from_args(Alloc&, T* address,                          \
    boost::unordered::detail::BOOST_PP_CAT(emplace_args, num_params) <         \
      BOOST_PP_ENUM_PARAMS_Z(z, num_params, A) > const& args)                  \
  {                                                                            \
    new ((void*)address)                                                       \
      T(BOOST_PP_ENUM_##z(num_params, BOOST_UNORDERED_CALL_FORWARD, args.a));  \
  }

        BOOST_UNORDERED_CONSTRUCT_IMPL(1, 4, _)
        BOOST_UNORDERED_CONSTRUCT_IMPL(1, 5, _)
        BOOST_UNORDERED_CONSTRUCT_IMPL(1, 6, _)
        BOOST_UNORDERED_CONSTRUCT_IMPL(1, 7, _)
        BOOST_UNORDERED_CONSTRUCT_IMPL(1, 8, _)
        BOOST_UNORDERED_CONSTRUCT_IMPL(1, 9, _)
        BOOST_PP_REPEAT_FROM_TO(10, BOOST_PP_INC(BOOST_UNORDERED_EMPLACE_LIMIT),
          BOOST_UNORDERED_CONSTRUCT_IMPL, _)

#undef BOOST_UNORDERED_CONSTRUCT_IMPL

        // Construct with piecewise_construct

        template <typename Alloc, typename A, typename B, typename A0,
          typename A1, typename A2>
        inline typename enable_if<use_piecewise<A0>, void>::type
        construct_from_args(Alloc& alloc, std::pair<A, B>* address,
          boost::unordered::detail::emplace_args3<A0, A1, A2> const& args)
        {
          boost::unordered::detail::func::construct_from_tuple(
            alloc, boost::addressof(address->first), args.a1);
          BOOST_TRY
          {
            boost::unordered::detail::func::construct_from_tuple(
              alloc, boost::addressof(address->second), args.a2);
          }
          BOOST_CATCH(...)
          {
            boost::unordered::detail::func::destroy(
              boost::addressof(address->first));
            BOOST_RETHROW
          }
          BOOST_CATCH_END
        }

#endif // BOOST_NO_CXX11_VARIADIC_TEMPLATES
      }
    }
  }
}

namespace boost {
  namespace unordered {
    namespace detail {

      ///////////////////////////////////////////////////////////////////
      //
      // Node construction

      template <typename NodeAlloc> struct node_constructor
      {
        typedef NodeAlloc node_allocator;
        typedef boost::unordered::detail::allocator_traits<NodeAlloc>
          node_allocator_traits;
        typedef typename node_allocator_traits::value_type node;
        typedef typename node_allocator_traits::pointer node_pointer;
        typedef typename node::value_type value_type;

        node_allocator& alloc_;
        node_pointer node_;

        node_constructor(node_allocator& n) : alloc_(n), node_() {}

        ~node_constructor();

        void create_node();

        // no throw
        node_pointer release()
        {
          BOOST_ASSERT(node_);
          node_pointer p = node_;
          node_ = node_pointer();
          return p;
        }

      private:
        node_constructor(node_constructor const&);
        node_constructor& operator=(node_constructor const&);
      };

      template <typename Alloc> node_constructor<Alloc>::~node_constructor()
      {
        if (node_) {
          boost::unordered::detail::func::destroy(boost::to_address(node_));
          node_allocator_traits::deallocate(alloc_, node_, 1);
        }
      }

      template <typename Alloc> void node_constructor<Alloc>::create_node()
      {
        BOOST_ASSERT(!node_);
        node_ = node_allocator_traits::allocate(alloc_, 1);
        new ((void*)boost::to_address(node_)) node();
      }

      template <typename NodeAlloc> struct node_tmp
      {
        typedef typename boost::allocator_value_type<NodeAlloc>::type node;
        typedef typename boost::allocator_pointer<NodeAlloc>::type node_pointer;
        typedef typename node::value_type value_type;
        typedef typename boost::allocator_rebind<NodeAlloc, value_type>::type
          value_allocator;

        NodeAlloc& alloc_;
        node_pointer node_;

        explicit node_tmp(node_pointer n, NodeAlloc& a) : alloc_(a), node_(n) {}

        ~node_tmp();

        // no throw
        node_pointer release()
        {
          node_pointer p = node_;
          node_ = node_pointer();
          return p;
        }
      };

      template <typename Alloc> node_tmp<Alloc>::~node_tmp()
      {
        if (node_) {
          value_allocator val_alloc(alloc_);
          boost::allocator_destroy(val_alloc, node_->value_ptr());
          boost::allocator_deallocate(alloc_, node_, 1);
        }
      }
    }
  }
}

namespace boost {
  namespace unordered {
    namespace detail {
      namespace func {

        // Some nicer construct_node functions, might try to
        // improve implementation later.

        template <typename Alloc, BOOST_UNORDERED_EMPLACE_TEMPLATE>
        inline typename boost::allocator_pointer<Alloc>::type
        construct_node_from_args(Alloc& alloc, BOOST_UNORDERED_EMPLACE_ARGS)
        {
          typedef typename boost::allocator_value_type<Alloc>::type node;
          typedef typename node::value_type value_type;
          typedef typename boost::allocator_rebind<Alloc, value_type>::type
            value_allocator;

          value_allocator val_alloc(alloc);

          node_constructor<Alloc> a(alloc);
          a.create_node();
          construct_from_args(
            val_alloc, a.node_->value_ptr(), BOOST_UNORDERED_EMPLACE_FORWARD);
          return a.release();
        }

        template <typename Alloc, typename U>
        inline typename boost::allocator_pointer<Alloc>::type construct_node(
          Alloc& alloc, BOOST_FWD_REF(U) x)
        {
          node_constructor<Alloc> a(alloc);
          a.create_node();

          typedef typename boost::allocator_value_type<Alloc>::type node;
          typedef typename node::value_type value_type;
          typedef typename boost::allocator_rebind<Alloc, value_type>::type
            value_allocator;

          value_allocator val_alloc(alloc);

          boost::allocator_construct(
            val_alloc, a.node_->value_ptr(), boost::forward<U>(x));
          return a.release();
        }

#if BOOST_UNORDERED_CXX11_CONSTRUCTION

        template <typename Alloc, typename Key>
        inline typename boost::allocator_pointer<Alloc>::type
        construct_node_pair(Alloc& alloc, BOOST_FWD_REF(Key) k)
        {
          node_constructor<Alloc> a(alloc);
          a.create_node();

          typedef typename boost::allocator_value_type<Alloc>::type node;
          typedef typename node::value_type value_type;
          typedef typename boost::allocator_rebind<Alloc, value_type>::type
            value_allocator;

          value_allocator val_alloc(alloc);

          boost::allocator_construct(
            val_alloc, a.node_->value_ptr(), std::piecewise_construct,
            std::forward_as_tuple(boost::forward<Key>(k)),
            std::forward_as_tuple());
          return a.release();
        }

        template <typename Alloc, typename Key, typename Mapped>
        inline typename boost::allocator_pointer<Alloc>::type
        construct_node_pair(
          Alloc& alloc, BOOST_FWD_REF(Key) k, BOOST_FWD_REF(Mapped) m)
        {
          node_constructor<Alloc> a(alloc);
          a.create_node();

          typedef typename boost::allocator_value_type<Alloc>::type node;
          typedef typename node::value_type value_type;
          typedef typename boost::allocator_rebind<Alloc, value_type>::type
            value_allocator;

          value_allocator val_alloc(alloc);

          boost::allocator_construct(val_alloc, a.node_->value_ptr(),
            std::piecewise_construct,
            std::forward_as_tuple(boost::forward<Key>(k)),
            std::forward_as_tuple(boost::forward<Mapped>(m)));
          return a.release();
        }

        template <typename Alloc, typename Key, typename... Args>
        inline typename boost::allocator_pointer<Alloc>::type
        construct_node_pair_from_args(
          Alloc& alloc, BOOST_FWD_REF(Key) k, BOOST_FWD_REF(Args)... args)
        {
          node_constructor<Alloc> a(alloc);
          a.create_node();
#if !(BOOST_COMP_CLANG && BOOST_COMP_CLANG < BOOST_VERSION_NUMBER(3, 8, 0) &&  \
      defined(BOOST_LIBSTDCXX11))

          typedef typename boost::allocator_value_type<Alloc>::type node;
          typedef typename node::value_type value_type;
          typedef typename boost::allocator_rebind<Alloc, value_type>::type
            value_allocator;

          value_allocator val_alloc(alloc);

          boost::allocator_construct(val_alloc, a.node_->value_ptr(),
            std::piecewise_construct,
            std::forward_as_tuple(boost::forward<Key>(k)),
            std::forward_as_tuple(boost::forward<Args>(args)...));
#else
          // It doesn't seem to be possible to construct a tuple with 3 variadic
          // rvalue reference members when using older versions of clang with
          // libstdc++, so just use std::make_tuple instead of
          // std::forward_as_tuple.
          boost::allocator_construct(val_alloc, a.node_->value_ptr(),
            std::piecewise_construct,
            std::forward_as_tuple(boost::forward<Key>(k)),
            std::make_tuple(boost::forward<Args>(args)...));
#endif
          return a.release();
        }

#else

        template <typename Alloc, typename Key>
        inline
          typename boost::unordered::detail::allocator_traits<Alloc>::pointer
          construct_node_pair(Alloc& alloc, BOOST_FWD_REF(Key) k)
        {
          node_constructor<Alloc> a(alloc);
          a.create_node();
          boost::unordered::detail::func::construct_value(
            boost::addressof(a.node_->value_ptr()->first),
            boost::forward<Key>(k));
          BOOST_TRY
          {
            boost::unordered::detail::func::construct_value(
              boost::addressof(a.node_->value_ptr()->second));
          }
          BOOST_CATCH(...)
          {
            boost::unordered::detail::func::destroy(
              boost::addressof(a.node_->value_ptr()->first));
            BOOST_RETHROW
          }
          BOOST_CATCH_END
          return a.release();
        }

        template <typename Alloc, typename Key, typename Mapped>
        inline
          typename boost::unordered::detail::allocator_traits<Alloc>::pointer
          construct_node_pair(
            Alloc& alloc, BOOST_FWD_REF(Key) k, BOOST_FWD_REF(Mapped) m)
        {
          node_constructor<Alloc> a(alloc);
          a.create_node();
          boost::unordered::detail::func::construct_value(
            boost::addressof(a.node_->value_ptr()->first),
            boost::forward<Key>(k));
          BOOST_TRY
          {
            boost::unordered::detail::func::construct_value(
              boost::addressof(a.node_->value_ptr()->second),
              boost::forward<Mapped>(m));
          }
          BOOST_CATCH(...)
          {
            boost::unordered::detail::func::destroy(
              boost::addressof(a.node_->value_ptr()->first));
            BOOST_RETHROW
          }
          BOOST_CATCH_END
          return a.release();
        }

        template <typename Alloc, typename Key,
          BOOST_UNORDERED_EMPLACE_TEMPLATE>
        inline
          typename boost::unordered::detail::allocator_traits<Alloc>::pointer
          construct_node_pair_from_args(
            Alloc& alloc, BOOST_FWD_REF(Key) k, BOOST_UNORDERED_EMPLACE_ARGS)
        {
          node_constructor<Alloc> a(alloc);
          a.create_node();
          boost::unordered::detail::func::construct_value(
            boost::addressof(a.node_->value_ptr()->first),
            boost::forward<Key>(k));
          BOOST_TRY
          {
            boost::unordered::detail::func::construct_from_args(alloc,
              boost::addressof(a.node_->value_ptr()->second),
              BOOST_UNORDERED_EMPLACE_FORWARD);
          }
          BOOST_CATCH(...)
          {
            boost::unordered::detail::func::destroy(
              boost::addressof(a.node_->value_ptr()->first));
            BOOST_RETHROW
          }
          BOOST_CATCH_END
          return a.release();
        }

#endif
      }
    }
  }
}

#if defined(BOOST_MSVC)
#pragma warning(pop)
#endif

namespace boost {
  namespace unordered {
    namespace detail {
      //////////////////////////////////////////////////////////////////////////
      // Functions
      //
      // This double buffers the storage for the hash function and key equality
      // predicate in order to have exception safe copy/swap. To do so,
      // use 'construct_spare' to construct in the spare space, and then when
      // ready to use 'switch_functions' to switch to the new functions.
      // If an exception is thrown between these two calls, use
      // 'cleanup_spare_functions' to destroy the unused constructed functions.

      template <class H, class P> class functions
      {
      public:
        static const bool nothrow_move_assignable =
          boost::is_nothrow_move_assignable<H>::value &&
          boost::is_nothrow_move_assignable<P>::value;
        static const bool nothrow_move_constructible =
          boost::is_nothrow_move_constructible<H>::value &&
          boost::is_nothrow_move_constructible<P>::value;
        static const bool nothrow_swappable =
          boost::is_nothrow_swappable<H>::value &&
          boost::is_nothrow_swappable<P>::value;

      private:
        functions& operator=(functions const&);

        typedef compressed<H, P> function_pair;

        typedef typename boost::aligned_storage<sizeof(function_pair),
          boost::alignment_of<function_pair>::value>::type aligned_function;

        unsigned char current_; // 0/1 - Currently active functions
                                // +2 - Both constructed
        aligned_function funcs_[2];

      public:
        functions(H const& hf, P const& eq) : current_(0)
        {
          construct_functions(current_, hf, eq);
        }

        functions(functions const& bf) : current_(0)
        {
          construct_functions(current_, bf.current_functions());
        }

        functions(functions& bf, boost::unordered::detail::move_tag)
            : current_(0)
        {
          construct_functions(current_, bf.current_functions(),
            boost::unordered::detail::integral_constant<bool,
              nothrow_move_constructible>());
        }

        ~functions()
        {
          BOOST_ASSERT(!(current_ & 2));
          destroy_functions(current_);
        }

        H const& hash_function() const { return current_functions().first(); }

        P const& key_eq() const { return current_functions().second(); }

        function_pair const& current_functions() const
        {
          return *static_cast<function_pair const*>(
            static_cast<void const*>(funcs_[current_ & 1].address()));
        }

        function_pair& current_functions()
        {
          return *static_cast<function_pair*>(
            static_cast<void*>(funcs_[current_ & 1].address()));
        }

        void construct_spare_functions(function_pair const& f)
        {
          BOOST_ASSERT(!(current_ & 2));
          construct_functions(current_ ^ 1, f);
          current_ |= 2;
        }

        void cleanup_spare_functions()
        {
          if (current_ & 2) {
            current_ = static_cast<unsigned char>(current_ & 1);
            destroy_functions(current_ ^ 1);
          }
        }

        void switch_functions()
        {
          BOOST_ASSERT(current_ & 2);
          destroy_functions(static_cast<unsigned char>(current_ & 1));
          current_ ^= 3;
        }

      private:
        void construct_functions(unsigned char which, H const& hf, P const& eq)
        {
          BOOST_ASSERT(!(which & 2));
          new ((void*)&funcs_[which]) function_pair(hf, eq);
        }

        void construct_functions(unsigned char which, function_pair const& f,
          boost::unordered::detail::false_type =
            boost::unordered::detail::false_type())
        {
          BOOST_ASSERT(!(which & 2));
          new ((void*)&funcs_[which]) function_pair(f);
        }

        void construct_functions(unsigned char which, function_pair& f,
          boost::unordered::detail::true_type)
        {
          BOOST_ASSERT(!(which & 2));
          new ((void*)&funcs_[which])
            function_pair(f, boost::unordered::detail::move_tag());
        }

        void destroy_functions(unsigned char which)
        {
          BOOST_ASSERT(!(which & 2));
          boost::unordered::detail::func::destroy(
            (function_pair*)(&funcs_[which]));
        }
      };

////////////////////////////////////////////////////////////////////////////
// rvalue parameters when type can't be a BOOST_RV_REF(T) parameter
// e.g. for int

#if !defined(BOOST_NO_CXX11_RVALUE_REFERENCES)
#define BOOST_UNORDERED_RV_REF(T) BOOST_RV_REF(T)
#else
      struct please_ignore_this_overload
      {
        typedef please_ignore_this_overload type;
      };

      template <typename T> struct rv_ref_impl
      {
        typedef BOOST_RV_REF(T) type;
      };

      template <typename T>
      struct rv_ref
        : boost::detail::if_true<boost::is_class<T>::value>::
            BOOST_NESTED_TEMPLATE then<boost::unordered::detail::rv_ref_impl<T>,
              please_ignore_this_overload>::type
      {
      };

#define BOOST_UNORDERED_RV_REF(T)                                              \
  typename boost::unordered::detail::rv_ref<T>::type
#endif

#if defined(BOOST_MSVC)
#pragma warning(push)
#pragma warning(disable : 4127) // conditional expression is constant
#endif

      //////////////////////////////////////////////////////////////////////////
      // convert double to std::size_t

      inline std::size_t double_to_size(double f)
      {
        return f >= static_cast<double>(
                      (std::numeric_limits<std::size_t>::max)())
                 ? (std::numeric_limits<std::size_t>::max)()
                 : static_cast<std::size_t>(f);
      }

      //////////////////////////////////////////////////////////////////////////
      // iterator definitions

      namespace iterator_detail {
        template <class Node, class Bucket> class c_iterator;

        template <class Node, class Bucket>
        class iterator
            : public boost::iterator_facade<iterator<Node, Bucket>,
                typename Node::value_type, boost::forward_traversal_tag>
        {
        public:
          typedef typename Node::value_type value_type;
          typedef value_type element_type;
          typedef value_type* pointer;
          typedef value_type& reference;
          typedef std::ptrdiff_t difference_type;
          typedef std::forward_iterator_tag iterator_category;

          iterator() : p(), itb(){};

        private:
          typedef typename Node::node_pointer node_pointer;
          typedef grouped_bucket_iterator<Bucket> bucket_iterator;

          node_pointer p;
          bucket_iterator itb;

          template <class Types> friend struct boost::unordered::detail::table;
          template <class N, class B> friend class c_iterator;
          friend class boost::iterator_core_access;

          iterator(node_pointer p_, bucket_iterator itb_) : p(p_), itb(itb_) {}

          value_type& dereference() const BOOST_NOEXCEPT { return p->value(); }

          bool equal(const iterator& x) const BOOST_NOEXCEPT
          {
            return (p == x.p);
          }

          void increment() BOOST_NOEXCEPT
          {
            p = p->next;
            if (!p) {
              p = (++itb)->next;
            }
          }
        };

        template <class Node, class Bucket>
        class c_iterator
            : public boost::iterator_facade<c_iterator<Node, Bucket>,
                typename Node::value_type const, boost::forward_traversal_tag>
        {
        public:
          typedef typename Node::value_type value_type;
          typedef value_type const element_type;
          typedef value_type const* pointer;
          typedef value_type const& reference;
          typedef std::ptrdiff_t difference_type;
          typedef std::forward_iterator_tag iterator_category;

          c_iterator() : p(), itb(){};
          c_iterator(iterator<Node, Bucket> it) : p(it.p), itb(it.itb){};

        private:
          typedef typename Node::node_pointer node_pointer;
          typedef grouped_bucket_iterator<Bucket> bucket_iterator;

          node_pointer p;
          bucket_iterator itb;

          template <class Types> friend struct boost::unordered::detail::table;
          friend class boost::iterator_core_access;

          c_iterator(node_pointer p_, bucket_iterator itb_) : p(p_), itb(itb_)
          {
          }

          value_type const& dereference() const BOOST_NOEXCEPT
          {
            return p->value();
          }

          bool equal(const c_iterator& x) const BOOST_NOEXCEPT
          {
            return (p == x.p);
          }

          void increment() BOOST_NOEXCEPT
          {
            p = p->next;
            if (!p) {
              p = (++itb)->next;
            }
          }
        };
      } // namespace iterator_detail

      //////////////////////////////////////////////////////////////////////////
      // table structure used by the containers
      template <typename Types>
      struct table : boost::unordered::detail::functions<typename Types::hasher,
                       typename Types::key_equal>
      {
      private:
        table(table const&);
        table& operator=(table const&);

      public:
        typedef typename Types::hasher hasher;
        typedef typename Types::key_equal key_equal;
        typedef typename Types::const_key_type const_key_type;
        typedef typename Types::extractor extractor;
        typedef typename Types::value_type value_type;
        typedef typename Types::table table_impl;

        typedef boost::unordered::detail::functions<typename Types::hasher,
          typename Types::key_equal>
          functions;

        typedef typename Types::value_allocator value_allocator;
        typedef typename boost::allocator_void_pointer<value_allocator>::type void_pointer;
        typedef node<value_type, void_pointer> node_type;

        typedef boost::unordered::detail::grouped_bucket_array<
          bucket<node_type, void_pointer>, value_allocator, prime_fmod_size<> >
          bucket_array_type;

        typedef typename bucket_array_type::node_allocator_type
          node_allocator_type;
        typedef typename boost::allocator_pointer<node_allocator_type>::type node_pointer;

        typedef boost::unordered::detail::node_constructor<node_allocator_type>
          node_constructor;
        typedef boost::unordered::detail::node_tmp<node_allocator_type> node_tmp;

        typedef typename bucket_array_type::bucket_type bucket_type;

        typedef typename bucket_array_type::iterator bucket_iterator;

        typedef typename bucket_array_type::local_iterator l_iterator;
        typedef typename bucket_array_type::const_local_iterator cl_iterator;

        typedef std::size_t size_type;

        typedef iterator_detail::iterator<node_type, bucket_type> iterator;
        typedef iterator_detail::c_iterator<node_type, bucket_type> c_iterator;

        typedef std::pair<iterator, bool> emplace_return;

        ////////////////////////////////////////////////////////////////////////
        // Members

        std::size_t size_;
        float mlf_;
        std::size_t max_load_;
        bucket_array_type buckets_;

      public:
        ////////////////////////////////////////////////////////////////////////
        // Data access

        size_type bucket_count() const { return buckets_.bucket_count(); }

        template <class Key>
        iterator next_group(Key const& k, c_iterator n) const
        {
          c_iterator last = this->end();
          while (n != last && this->key_eq()(k, extractor::extract(*n))) {
            ++n;
          }
          return iterator(n.p, n.itb);
        }

        template <class Key> std::size_t group_count(Key const& k) const
        {
          if (size_ == 0) {
            return 0;
          }
          std::size_t c = 0;
          std::size_t const key_hash = this->hash(k);
          bucket_iterator itb =
            buckets_.at(buckets_.position(key_hash));

          bool found = false;

          for (node_pointer pos = itb->next; pos; pos = pos->next) {
            if (this->key_eq()(k, this->get_key(pos))) {
              ++c;
              found = true;
            } else if (found) {
              break;
            }
          }
          return c;
        }

        node_allocator_type const& node_alloc() const
        {
          return buckets_.get_node_allocator();
        }

        node_allocator_type& node_alloc()
        {
          return buckets_.get_node_allocator();
        }

        std::size_t max_bucket_count() const
        {
          typedef typename bucket_array_type::size_policy size_policy;
          return size_policy::size(size_policy::size_index(
            boost::allocator_max_size(this->node_alloc())));
        }

        iterator begin() const
        {
          if (size_ == 0) {
            return end();
          }

          bucket_iterator itb = buckets_.begin();
          return iterator(itb->next, itb);
        }

        iterator end() const
        {
          return iterator();
        }

        l_iterator begin(std::size_t bucket_index) const
        {
          return buckets_.begin(bucket_index);
        }

        std::size_t hash_to_bucket(std::size_t hash_value) const
        {
          return buckets_.position(hash_value);
        }

        std::size_t bucket_size(std::size_t index) const
        {
          bucket_iterator itb = buckets_.at(index);
          node_pointer n = itb->next;
          std::size_t count = 0;
          while (n) {
            ++count;
            n = n->next;
          }
          return count;
        }

        ////////////////////////////////////////////////////////////////////////
        // Load methods

        void recalculate_max_load()
        {
          using namespace std;

          // From 6.3.1/13:
          // Only resize when size >= mlf_ * count
          max_load_ = boost::unordered::detail::double_to_size(
            floor(static_cast<double>(mlf_) *
                 static_cast<double>(buckets_.bucket_count())));
        }

        void max_load_factor(float z)
        {
          BOOST_ASSERT(z > 0);
          mlf_ = (std::max)(z, minimum_max_load_factor);
          recalculate_max_load();
        }

        ////////////////////////////////////////////////////////////////////////
        // Constructors

        table(std::size_t num_buckets, hasher const& hf, key_equal const& eq,
          node_allocator_type const& a)
            : functions(hf, eq), size_(0), mlf_(1.0f), max_load_(0),
              buckets_(num_buckets, a)
        {
          recalculate_max_load();
        }

        table(table const& x, node_allocator_type const& a)
            : functions(x), size_(0), mlf_(x.mlf_), max_load_(0),
              buckets_(x.size_, a)
        {
          recalculate_max_load();
        }

        table(table& x, boost::unordered::detail::move_tag m)
            : functions(x, m), size_(x.size_), mlf_(x.mlf_),
              max_load_(x.max_load_), buckets_(boost::move(x.buckets_))
        {
          x.size_ = 0;
          x.max_load_ = 0;
        }

        table(table& x, node_allocator_type const& a,
          boost::unordered::detail::move_tag m)
            : functions(x, m), size_(0), mlf_(x.mlf_), max_load_(0),
              buckets_(x.bucket_count(), a)
        {
          recalculate_max_load();
        }

        ////////////////////////////////////////////////////////////////////////
        // Swap and Move

        void swap_allocators(table& other, false_type)
        {
          boost::unordered::detail::func::ignore_unused_variable_warning(other);

          // According to 23.2.1.8, if propagate_on_container_swap is
          // false the behaviour is undefined unless the allocators
          // are equal.
          BOOST_ASSERT(node_alloc() == other.node_alloc());
        }

        // Not nothrow swappable
        void swap(table& x, false_type)
        {
          if (this == &x) {
            return;
          }

          this->construct_spare_functions(x.current_functions());
          BOOST_TRY { x.construct_spare_functions(this->current_functions()); }
          BOOST_CATCH(...)
          {
            this->cleanup_spare_functions();
            BOOST_RETHROW
          }
          BOOST_CATCH_END
          this->switch_functions();
          x.switch_functions();

          buckets_.swap(x.buckets_);
          boost::swap(size_, x.size_);
          std::swap(mlf_, x.mlf_);
          std::swap(max_load_, x.max_load_);
        }

        // Nothrow swappable
        void swap(table& x, true_type)
        {
          buckets_.swap(x.buckets_);
          boost::swap(size_, x.size_);
          std::swap(mlf_, x.mlf_);
          std::swap(max_load_, x.max_load_);
          this->current_functions().swap(x.current_functions());
        }

        // Only swaps the allocators if propagate_on_container_swap.
        // If not propagate_on_container_swap and allocators aren't
        // equal, behaviour is undefined.
        void swap(table& x)
        {
          BOOST_ASSERT(boost::allocator_propagate_on_container_swap<
                         node_allocator_type>::type::value ||
                       node_alloc() == x.node_alloc());
          swap(x, boost::unordered::detail::integral_constant<bool,
                    functions::nothrow_swappable>());
        }

        // Only call with nodes allocated with the currect allocator, or
        // one that is equal to it. (Can't assert because other's
        // allocators might have already been moved).
        void move_buckets_from(table& other)
        {
          buckets_ = boost::move(other.buckets_);

          size_ = other.size_;
          max_load_ = other.max_load_;

          other.size_ = 0;
          other.max_load_ = 0;
        }

        // For use in the constructor when allocators might be different.
        void move_construct_buckets(table& src)
        {
          if (this->node_alloc() == src.node_alloc()) {
            move_buckets_from(src);
            return;
          }

          if (src.size_ == 0) {
            return;
          }

          BOOST_ASSERT(
            buckets_.bucket_count() == src.buckets_.bucket_count());

          this->reserve(src.size_);
          for (iterator pos = src.begin(); pos != src.end(); ++pos) {
            node_tmp b(detail::func::construct_node(
                         this->node_alloc(), boost::move(pos.p->value())),
              this->node_alloc());

            const_key_type& k = this->get_key(b.node_);
            std::size_t key_hash = this->hash(k);

            bucket_iterator itb =
              buckets_.at(buckets_.position(key_hash));
            buckets_.insert_node(itb, b.release());
            ++size_;
          }
        }

        ////////////////////////////////////////////////////////////////////////
        // Delete/destruct

        ~table() { delete_buckets(); }

        void delete_node(node_pointer p)
        {
          node_allocator_type alloc = this->node_alloc();

          value_allocator val_alloc(alloc);
          boost::allocator_destroy(val_alloc, p->value_ptr());
          boost::allocator_deallocate(alloc, p, 1);
        }

        void delete_buckets()
        {
          iterator pos = begin(), last = this->end();
          for (; pos != last;) {
            node_pointer p = pos.p;
            bucket_iterator itb = pos.itb;
            ++pos;
            buckets_.extract_node(itb, p);
            delete_node(p);
            --size_;
          }

          buckets_.clear();
        }

        ////////////////////////////////////////////////////////////////////////
        // Clear

        void clear_impl();

        ////////////////////////////////////////////////////////////////////////
        // Assignment

        template <typename UniqueType>
        void assign(table const& x, UniqueType is_unique)
        {
          typedef typename boost::allocator_propagate_on_container_copy_assignment<node_allocator_type>::type pocca;

          if (this != &x) {
            assign(x, is_unique,
              boost::unordered::detail::integral_constant<bool,
                pocca::value>());
          }
        }

        template <typename UniqueType>
        void assign(table const &x, UniqueType is_unique, false_type)
        {
          // Strong exception safety.
          this->construct_spare_functions(x.current_functions());
          BOOST_TRY
          {
            mlf_ = x.mlf_;
            recalculate_max_load();

            this->reserve_for_insert(x.size_);
            this->clear_impl();
          }
          BOOST_CATCH(...)
          {
            this->cleanup_spare_functions();
            BOOST_RETHROW
          }
          BOOST_CATCH_END
          this->switch_functions();
          copy_buckets(x, is_unique);
        }

        template <typename UniqueType>
        void assign(table const &x, UniqueType is_unique, true_type)
        {
          if (node_alloc() == x.node_alloc())
          {
            buckets_.reset_allocator(x.node_alloc());
            assign(x, is_unique, false_type());
          }
          else
          {
            bucket_array_type new_buckets(x.size_, x.node_alloc());
            this->construct_spare_functions(x.current_functions());
            this->switch_functions();

            // Delete everything with current allocators before assigning
            // the new ones.
            delete_buckets();
            buckets_.reset_allocator(x.node_alloc());
            buckets_ = boost::move(new_buckets);

            // Copy over other data, all no throw.
            mlf_ = x.mlf_;
            reserve(x.size_);

            // Finally copy the elements.
            if (x.size_)
            {
              copy_buckets(x, is_unique);
            }
          }
        }

        template <typename UniqueType>
        void move_assign(table& x, UniqueType is_unique)
        {
          if (this != &x) {
            move_assign(x, is_unique,
              boost::unordered::detail::integral_constant<bool,
                boost::allocator_propagate_on_container_move_assignment<
                  node_allocator_type>::type::value>());
          }
        }

        // Propagate allocator
        template <typename UniqueType>
        void move_assign(table& x, UniqueType, true_type)
        {
          if (!functions::nothrow_move_assignable) {
            this->construct_spare_functions(x.current_functions());
            this->switch_functions();
          } else {
            this->current_functions().move_assign(x.current_functions());
          }
          delete_buckets();

          buckets_.reset_allocator(x.buckets_.get_node_allocator());
          mlf_ = x.mlf_;
          move_buckets_from(x);
        }

        // Don't propagate allocator
        template <typename UniqueType>
        void move_assign(table& x, UniqueType is_unique, false_type)
        {
          reserve(x.size_);
          if (node_alloc() == x.node_alloc()) {
            move_assign_equal_alloc(x);
          } else {
            move_assign_realloc(x, is_unique);
          }
        }

        void move_assign_equal_alloc(table& x)
        {
          if (!functions::nothrow_move_assignable) {
            this->construct_spare_functions(x.current_functions());
            this->switch_functions();
          } else {
            this->current_functions().move_assign(x.current_functions());
          }
          delete_buckets();
          mlf_ = x.mlf_;
          move_buckets_from(x);
        }

        template <typename UniqueType>
        void move_assign_realloc(table& x, UniqueType is_unique)
        {
          this->construct_spare_functions(x.current_functions());
          BOOST_TRY
          {
            mlf_ = x.mlf_;
            recalculate_max_load();
            this->reserve_for_insert(x.size_);
            this->clear_impl();
          }
          BOOST_CATCH(...)
          {
            this->cleanup_spare_functions();
            BOOST_RETHROW
          }
          BOOST_CATCH_END
          this->switch_functions();
          move_assign_buckets(x, is_unique);
        }

        // Accessors

        const_key_type& get_key(node_pointer n) const
        {
          return extractor::extract(n->value());
        }

        template <class Key>
        std::size_t hash(Key const& k) const
        {
          return this->hash_function()(k);
        }

        // Find Node

        template <class Key>
        node_pointer find_node_impl(
          Key const& x, bucket_iterator itb) const
        {
          key_equal const& pred = this->key_eq();
          node_pointer p = itb->next;
          for (; p; p = p->next) {
            if (pred(x, extractor::extract(p->value()))) {
              break;
            }
          }
          return p;
        }

        template <class Key> node_pointer find_node(Key const& k) const
        {
          std::size_t const key_hash = this->hash(k);
          return find_node_impl(
            k, buckets_.at(buckets_.position(key_hash)));
        }

        node_pointer find_node(
          const_key_type& k, bucket_iterator itb) const
        {
          return find_node_impl(k, itb);
        }

        template <class Key> iterator find(Key const& k) const
        {
          return this->transparent_find(
            k, this->hash_function(), this->key_eq());
        }

#if defined(BOOST_MSVC)
#pragma warning(push)
#pragma warning(                                                               \
  disable : 4714) // function 'function' marked as __forceinline not inlined
#endif
        template <class Key, class Hash, class Pred>
        BOOST_FORCEINLINE iterator transparent_find(
          Key const& k, Hash const& h, Pred const& pred) const
        {
          std::size_t const key_hash = h(k);
          bucket_iterator itb = buckets_.at(buckets_.position(key_hash));
          for (node_pointer p = itb->next; p; p = p->next) {
            if (BOOST_LIKELY(pred(k, extractor::extract(p->value())))) {
              return iterator(p, itb);
            }
          }

          return this->end();
        }

#if defined(BOOST_MSVC)
#pragma warning(pop)
#endif

        template <class Key>
        node_pointer* find_prev(Key const& key, bucket_iterator itb)
        {
          key_equal pred = this->key_eq();
          for (node_pointer* pp = boost::addressof(itb->next); *pp;
               pp = boost::addressof((*pp)->next)) {
            if (pred(key, extractor::extract((*pp)->value()))) {
              return pp;
            }
          }
          typedef node_pointer* node_pointer_pointer;
          return node_pointer_pointer();
        }

        // Extract and erase

        template <class Key> node_pointer extract_by_key_impl(Key const& k)
        {
          iterator it = this->find(k);
          if (it == this->end()) {
            return node_pointer();
          }

          buckets_.extract_node(it.itb, it.p);
          --size_;

          return it.p;
        }

        // Reserve and rehash
        void transfer_node(
          node_pointer p, bucket_type&, bucket_array_type& new_buckets)
        {
          const_key_type& key = extractor::extract(p->value());
          std::size_t const h = this->hash(key);
          bucket_iterator itnewb = new_buckets.at(new_buckets.position(h));
          new_buckets.insert_node(itnewb, p);
        }

        void rehash(std::size_t);
        void reserve(std::size_t);
        void reserve_for_insert(std::size_t);
        void rehash_impl(std::size_t);

        ////////////////////////////////////////////////////////////////////////
        // Unique keys

        // equals

        bool equals_unique(table const& other) const
        {
          if (this->size_ != other.size_)
            return false;

          c_iterator pos = this->begin();
          c_iterator last = this->end();

          while (pos != last) {
            node_pointer p = pos.p;
            node_pointer p2 = other.find_node(this->get_key(p));
            if (!p2 || !(p->value() == p2->value())) {
              return false;
            }
            ++pos;
          }

          return true;
        }

        // Emplace/Insert

        template <BOOST_UNORDERED_EMPLACE_TEMPLATE>
        iterator emplace_hint_unique(
          c_iterator hint, const_key_type& k, BOOST_UNORDERED_EMPLACE_ARGS)
        {
          if (hint.p && this->key_eq()(k, this->get_key(hint.p))) {
            return iterator(hint.p, hint.itb);
          } else {
            return emplace_unique(k, BOOST_UNORDERED_EMPLACE_FORWARD).first;
          }
        }

        template <BOOST_UNORDERED_EMPLACE_TEMPLATE>
        emplace_return emplace_unique(
          const_key_type& k, BOOST_UNORDERED_EMPLACE_ARGS)
        {
          std::size_t key_hash = this->hash(k);
          bucket_iterator itb =
            buckets_.at(buckets_.position(key_hash));
          node_pointer pos = this->find_node_impl(k, itb);

          if (pos) {
            return emplace_return(iterator(pos, itb), false);
          } else {
            node_tmp b(boost::unordered::detail::func::construct_node_from_args(
                         this->node_alloc(), BOOST_UNORDERED_EMPLACE_FORWARD),
              this->node_alloc());

            if (size_ + 1 > max_load_) {
              reserve(size_ + 1);
              itb = buckets_.at(buckets_.position(key_hash));
            }

            node_pointer p = b.release();
            buckets_.insert_node(itb, p);
            ++size_;

            return emplace_return(iterator(p, itb), true);
          }
        }

        template <BOOST_UNORDERED_EMPLACE_TEMPLATE>
        iterator emplace_hint_unique(
          c_iterator hint, no_key, BOOST_UNORDERED_EMPLACE_ARGS)
        {
          node_tmp b(boost::unordered::detail::func::construct_node_from_args(
                       this->node_alloc(), BOOST_UNORDERED_EMPLACE_FORWARD),
            this->node_alloc());

          const_key_type& k = this->get_key(b.node_);
          if (hint.p && this->key_eq()(k, this->get_key(hint.p))) {
            return iterator(hint.p, hint.itb);
          }

          std::size_t const key_hash = this->hash(k);
          bucket_iterator itb =
            buckets_.at(buckets_.position(key_hash));

          node_pointer p = this->find_node_impl(k, itb);
          if (p) {
            return iterator(p, itb);
          }

          if (size_ + 1 > max_load_) {
            this->reserve(size_ + 1);
            itb = buckets_.at(buckets_.position(key_hash));
          }

          p = b.release();
          buckets_.insert_node(itb, p);
          ++size_;
          return iterator(p, itb);
        }

        template <BOOST_UNORDERED_EMPLACE_TEMPLATE>
        emplace_return emplace_unique(no_key, BOOST_UNORDERED_EMPLACE_ARGS)
        {
          node_tmp b(boost::unordered::detail::func::construct_node_from_args(
                       this->node_alloc(), BOOST_UNORDERED_EMPLACE_FORWARD),
            this->node_alloc());

          const_key_type& k = this->get_key(b.node_);
          std::size_t key_hash = this->hash(k);

          bucket_iterator itb =
            buckets_.at(buckets_.position(key_hash));
          node_pointer pos = this->find_node_impl(k, itb);

          if (pos) {
            return emplace_return(iterator(pos, itb), false);
          } else {
            if (size_ + 1 > max_load_) {
              reserve(size_ + 1);
              itb = buckets_.at(buckets_.position(key_hash));
            }

            node_pointer p = b.release();
            buckets_.insert_node(itb, p);
            ++size_;

            return emplace_return(iterator(p, itb), true);
          }
        }

        template <typename Key>
        emplace_return try_emplace_unique(BOOST_FWD_REF(Key) k)
        {
          std::size_t key_hash = this->hash(k);
          bucket_iterator itb =
            buckets_.at(buckets_.position(key_hash));

          node_pointer pos = this->find_node_impl(k, itb);

          if (pos) {
            return emplace_return(iterator(pos, itb), false);
          } else {
            node_allocator_type alloc = node_alloc();

            node_tmp tmp(
              detail::func::construct_node_pair(alloc, boost::forward<Key>(k)),
              alloc);

            if (size_ + 1 > max_load_) {
              reserve(size_ + 1);
              itb = buckets_.at(buckets_.position(key_hash));
            }

            node_pointer p = tmp.release();
            buckets_.insert_node(itb, p);

            ++size_;
            return emplace_return(iterator(p, itb), true);
          }
        }

        template <typename Key>
        iterator try_emplace_hint_unique(c_iterator hint, BOOST_FWD_REF(Key) k)
        {
          if (hint.p && this->key_eq()(hint->first, k)) {
            return iterator(hint.p, hint.itb);
          } else {
            return try_emplace_unique(k).first;
          }
        }

        template <typename Key, BOOST_UNORDERED_EMPLACE_TEMPLATE>
        emplace_return try_emplace_unique(
          BOOST_FWD_REF(Key) k, BOOST_UNORDERED_EMPLACE_ARGS)
        {
          std::size_t key_hash = this->hash(k);
          bucket_iterator itb =
            buckets_.at(buckets_.position(key_hash));

          node_pointer pos = this->find_node_impl(k, itb);

          if (pos) {
            return emplace_return(iterator(pos, itb), false);
          }

          node_tmp b(
            boost::unordered::detail::func::construct_node_pair_from_args(
              this->node_alloc(), k, BOOST_UNORDERED_EMPLACE_FORWARD),
            this->node_alloc());

          if (size_ + 1 > max_load_) {
            reserve(size_ + 1);
            itb = buckets_.at(buckets_.position(key_hash));
          }

          pos = b.release();

          buckets_.insert_node(itb, pos);
          ++size_;
          return emplace_return(iterator(pos, itb), true);
        }

        template <typename Key, BOOST_UNORDERED_EMPLACE_TEMPLATE>
        iterator try_emplace_hint_unique(
          c_iterator hint, BOOST_FWD_REF(Key) k, BOOST_UNORDERED_EMPLACE_ARGS)
        {
          if (hint.p && this->key_eq()(hint->first, k)) {
            return iterator(hint.p, hint.itb);
          } else {
            return try_emplace_unique(k, BOOST_UNORDERED_EMPLACE_FORWARD).first;
          }
        }

        template <typename Key, typename M>
        emplace_return insert_or_assign_unique(
          BOOST_FWD_REF(Key) k, BOOST_FWD_REF(M) obj)
        {
          std::size_t key_hash = this->hash(k);
          bucket_iterator itb =
            buckets_.at(buckets_.position(key_hash));

          node_pointer p = this->find_node_impl(k, itb);
          if (p) {
            p->value().second = boost::forward<M>(obj);
            return emplace_return(iterator(p, itb), false);
          }

          node_tmp b(boost::unordered::detail::func::construct_node_pair(
                       this->node_alloc(), boost::forward<Key>(k),
                       boost::forward<M>(obj)),
            node_alloc());

          if (size_ + 1 > max_load_) {
            reserve(size_ + 1);
            itb = buckets_.at(buckets_.position(key_hash));
          }

          p = b.release();

          buckets_.insert_node(itb, p);
          ++size_;
          return emplace_return(iterator(p, itb), true);
        }

        template <typename NodeType, typename InsertReturnType>
        void move_insert_node_type_unique(
          NodeType& np, InsertReturnType& result)
        {
          if (!np) {
            result.position = this->end();
            result.inserted = false;
            return;
          }

          const_key_type& k = this->get_key(np.ptr_);
          std::size_t const key_hash = this->hash(k);
          bucket_iterator itb =
            buckets_.at(buckets_.position(key_hash));
          node_pointer p = this->find_node_impl(k, itb);

          if (p) {
            iterator pos(p, itb);
            result.node = boost::move(np);
            result.position = pos;
            result.inserted = false;
            return;
          }

          this->reserve_for_insert(size_ + 1);

          p = np.ptr_;
          itb = buckets_.at(buckets_.position(key_hash));

          buckets_.insert_node(itb, p);
          np.ptr_ = node_pointer();
          ++size_;

          result.position = iterator(p, itb);
          result.inserted = true;
        }

        template <typename NodeType>
        iterator move_insert_node_type_with_hint_unique(
          c_iterator hint, NodeType& np)
        {
          if (!np) {
            return this->end();
          }

          const_key_type& k = this->get_key(np.ptr_);
          if (hint.p && this->key_eq()(k, this->get_key(hint.p))) {
            return iterator(hint.p, hint.itb);
          }

          std::size_t const key_hash = this->hash(k);
          bucket_iterator itb =
            buckets_.at(buckets_.position(key_hash));
          node_pointer p = this->find_node_impl(k, itb);
          if (p) {
            return iterator(p, itb);
          }

          p = np.ptr_;

          if (size_ + 1 > max_load_) {
            this->reserve(size_ + 1);
            itb = buckets_.at(buckets_.position(key_hash));
          }

          buckets_.insert_node(itb, p);
          ++size_;
          np.ptr_ = node_pointer();
          return iterator(p, itb);
        }

        template <typename Types2>
        void merge_unique(boost::unordered::detail::table<Types2>& other)
        {
          typedef boost::unordered::detail::table<Types2> other_table;
          BOOST_STATIC_ASSERT((boost::is_same<node_type,
            typename other_table::node_type>::value));
          BOOST_ASSERT(this->node_alloc() == other.node_alloc());

          if (other.size_ == 0) {
            return;
          }

          this->reserve_for_insert(size_ + other.size_);

          iterator last = other.end();
          for (iterator pos = other.begin(); pos != last;) {
            const_key_type& key = other.get_key(pos.p);
            std::size_t const key_hash = this->hash(key);

            bucket_iterator itb =
              buckets_.at(buckets_.position(key_hash));

            if (this->find_node_impl(key, itb)) {
              ++pos;
              continue;
            }

            iterator old = pos;
            ++pos;

            node_pointer p = other.extract_by_iterator_unique(old);
            buckets_.insert_node(itb, p);
            ++size_;
          }
        }

        ////////////////////////////////////////////////////////////////////////
        // Insert range methods
        //
        // if hash function throws, or inserting > 1 element, basic exception
        // safety strong otherwise

        template <class InputIt>
        void insert_range_unique(no_key, InputIt i, InputIt j)
        {
          hasher const& hf = this->hash_function();
          node_allocator_type alloc = this->node_alloc();

          for (; i != j; ++i) {
            node_tmp tmp(detail::func::construct_node(alloc, *i), alloc);

            value_type const& value = tmp.node_->value();
            const_key_type& key = extractor::extract(value);
            std::size_t const h = hf(key);

            bucket_iterator itb = buckets_.at(buckets_.position(h));
            node_pointer it = find_node_impl(key, itb);
            if (it) {
              continue;
            }

            if (size_ + 1 > max_load_) {
              reserve(size_ + 1);
              itb = buckets_.at(buckets_.position(h));
            }

            node_pointer nptr = tmp.release();
            buckets_.insert_node(itb, nptr);
            ++size_;
          }
        }

        ////////////////////////////////////////////////////////////////////////
        // Extract

        inline node_pointer extract_by_iterator_unique(c_iterator i)
        {
          node_pointer p = i.p;
          bucket_iterator itb = i.itb;

          buckets_.extract_node(itb, p);
          --size_;

          return p;
        }

        ////////////////////////////////////////////////////////////////////////
        // Erase
        //

        template <class Key> std::size_t erase_key_unique_impl(Key const& k)
        {
          bucket_iterator itb = buckets_.at(buckets_.position(this->hash(k)));
          node_pointer* pp = this->find_prev(k, itb);
          if (!pp) {
            return 0;
          }

          node_pointer p = *pp;
          buckets_.extract_node_after(itb, pp);
          this->delete_node(p);
          --size_;
          return 1;
        }

        iterator erase_nodes_range(c_iterator first, c_iterator last)
        {
          if (first == last) {
            return iterator(last.p, last.itb);
          }

          // though `first` stores of a copy of a pointer to a node, we wish to
          // mutate the pointers stored internally by the singly-linked list in
          // each bucket group so we have to retrieve it manually by iterating
          //
          bucket_iterator itb = first.itb;
          node_pointer* pp = boost::addressof(itb->next);
          while (*pp != first.p) {
            pp = boost::addressof((*pp)->next);
          }

          while (*pp != last.p) {
            node_pointer p = *pp;
            *pp = (*pp)->next;

            this->delete_node(p);
            --size_;


            bool const at_end = !(*pp);
            bool const is_empty_bucket = !itb->next;

            if (at_end) {
              if (is_empty_bucket) {
                buckets_.unlink_bucket(itb++);
              } else {
                ++itb;
              }
              pp = boost::addressof(itb->next);
            }
          }

          return iterator(last.p, last.itb);
        }

        ////////////////////////////////////////////////////////////////////////
        // fill_buckets_unique

        void copy_buckets(table const& src, true_type)
        {
          BOOST_ASSERT(size_ == 0);

          this->reserve_for_insert(src.size_);

          for (iterator pos = src.begin(); pos != src.end(); ++pos) {
            value_type const& value = *pos;
            const_key_type& key = extractor::extract(value);
            std::size_t const key_hash = this->hash(key);

            bucket_iterator itb = buckets_.at(buckets_.position(key_hash));

            node_allocator_type alloc = this->node_alloc();
            node_tmp tmp(detail::func::construct_node(alloc, value), alloc);

            buckets_.insert_node(itb, tmp.release());
            ++size_;
          }
        }

        void move_assign_buckets(table& src, true_type)
        {
          BOOST_ASSERT(size_ == 0);
          BOOST_ASSERT(max_load_ >= src.size_);

          iterator last = src.end();
          node_allocator_type alloc = this->node_alloc();

          for (iterator pos = src.begin(); pos != last; ++pos) {
            value_type value = boost::move(*pos);
            const_key_type& key = extractor::extract(value);
            std::size_t const key_hash = this->hash(key);

            bucket_iterator itb = buckets_.at(buckets_.position(key_hash));

            node_tmp tmp(
              detail::func::construct_node(alloc, boost::move(value)), alloc);

            buckets_.insert_node(itb, tmp.release());
            ++size_;
          }
        }

        ////////////////////////////////////////////////////////////////////////
        // Equivalent keys

        // Equality

        bool equals_equiv(table const& other) const
        {
          if (this->size_ != other.size_)
            return false;

          iterator last = this->end();
          for (iterator n1 = this->begin(); n1 != last;) {
            const_key_type& k = extractor::extract(*n1);
            iterator n2 = other.find(k);
            if (n2 == other.end()) {
              return false;
            }

            iterator end1 = this->next_group(k, n1);
            iterator end2 = other.next_group(k, n2);

            if (!group_equals_equiv(n1, end1, n2, end2)) {
              return false;
            }

            n1 = end1;
          }

          return true;
        }

        static bool group_equals_equiv(iterator n1, iterator end1,
          iterator n2, iterator end2)
        {
          for (;;) {
            if (*n1 != *n2)
              break;

            ++n1;
            ++n2;

            if (n1 == end1)
              return n2 == end2;

            if (n2 == end2)
              return false;
          }

          for (iterator n1a = n1, n2a = n2;;) {
            ++n1a;
            ++n2a;

            if (n1a == end1) {
              if (n2a == end2)
                break;
              else
                return false;
            }

            if (n2a == end2)
              return false;
          }

          iterator start = n1;
          for (; n1 != end1; ++n1) {
            value_type const& v = *n1;
            if (!find_equiv(start, n1, v)) {
              std::size_t matches = count_equal_equiv(n2, end2, v);
              if (!matches)
                return false;

              iterator t = n1;
              if (matches != 1 + count_equal_equiv(++t, end1, v))
                return false;
            }
          }

          return true;
        }

        static bool find_equiv(
          iterator n, iterator last, value_type const& v)
        {
          for (; n != last; ++n)
            if (*n == v)
              return true;
          return false;
        }

        static std::size_t count_equal_equiv(
          iterator n, iterator last, value_type const& v)
        {
          std::size_t count = 0;
          for (; n != last; ++n)
            if (*n == v)
              ++count;
          return count;
        }

        // Emplace/Insert

        iterator emplace_equiv(node_pointer n)
        {
          node_tmp a(n, this->node_alloc());
          const_key_type& k = this->get_key(a.node_);
          std::size_t key_hash = this->hash(k);
          bucket_iterator itb =
            buckets_.at(buckets_.position(key_hash));
          node_pointer hint = this->find_node_impl(k, itb);

          if (size_ + 1 > max_load_) {
            this->reserve(size_ + 1);
            itb = buckets_.at(buckets_.position(key_hash));
          }
          node_pointer p = a.release();
          buckets_.insert_node_hint(itb, p, hint);
          ++size_;
          return iterator(p, itb);
        }

        iterator emplace_hint_equiv(c_iterator hint, node_pointer n)
        {
          node_tmp a(n, this->node_alloc());
          const_key_type& k = this->get_key(a.node_);
          bucket_iterator itb = hint.itb;
          node_pointer p = hint.p;

          std::size_t key_hash = 0u;

          bool const needs_rehash = (size_ + 1 > max_load_);
          bool const usable_hint = (p && this->key_eq()(k, this->get_key(p)));

          if (!usable_hint) {
            key_hash = this->hash(k);
            itb = buckets_.at(buckets_.position(key_hash));
            p = this->find_node_impl(k, itb);
          } else if (usable_hint && needs_rehash) {
            key_hash = this->hash(k);
          }

          if (needs_rehash) {
            this->reserve(size_ + 1);
            itb = buckets_.at(buckets_.position(key_hash));
          }

          a.release();
          buckets_.insert_node_hint(itb, n, p);
          ++size_;
          return iterator(n, itb);
        }

        void emplace_no_rehash_equiv(node_pointer n)
        {
          BOOST_ASSERT(size_ + 1 <= max_load_);
          node_tmp a(n, this->node_alloc());
          const_key_type& k = this->get_key(a.node_);
          std::size_t key_hash = this->hash(k);
          bucket_iterator itb = buckets_.at(buckets_.position(key_hash));
          node_pointer hint = this->find_node_impl(k, itb);
          node_pointer p = a.release();
          buckets_.insert_node_hint(itb, p, hint);
          ++size_;
        }

        template <typename NodeType>
        iterator move_insert_node_type_equiv(NodeType& np)
        {
          iterator result;

          if (np) {
            this->reserve_for_insert(size_ + 1);

            const_key_type& k = this->get_key(np.ptr_);
            std::size_t key_hash = this->hash(k);

            bucket_iterator itb =
              buckets_.at(buckets_.position(key_hash));

            node_pointer hint = this->find_node_impl(k, itb);
            buckets_.insert_node_hint(itb, np.ptr_, hint);
            ++size_;

            result = iterator(np.ptr_, itb);
            np.ptr_ = node_pointer();
          }

          return result;
        }

        template <typename NodeType>
        iterator move_insert_node_type_with_hint_equiv(
          c_iterator hint, NodeType& np)
        {
          iterator result;
          if (np) {
            bucket_iterator itb = hint.itb;
            node_pointer pos = hint.p;
            const_key_type& k = this->get_key(np.ptr_);
            std::size_t key_hash = this->hash(k);
            if (size_ + 1 > max_load_) {
              this->reserve(size_ + 1);
              itb = buckets_.at(buckets_.position(key_hash));
            }

            if (hint.p && this->key_eq()(k, this->get_key(hint.p))) {
            } else {
              itb = buckets_.at(buckets_.position(key_hash));
              pos = this->find_node_impl(k, itb);
            }
            buckets_.insert_node_hint(itb, np.ptr_, pos);
            ++size_;
            result = iterator(np.ptr_, itb);

            np.ptr_ = node_pointer();
          }

          return result;
        }

        ////////////////////////////////////////////////////////////////////////
        // Insert range methods

        // if hash function throws, or inserting > 1 element, basic exception
        // safety. Strong otherwise
        template <class I>
        typename boost::unordered::detail::enable_if_forward<I, void>::type
        insert_range_equiv(I i, I j)
        {
          if (i == j)
            return;

          std::size_t distance = static_cast<std::size_t>(std::distance(i, j));
          if (distance == 1) {
            emplace_equiv(boost::unordered::detail::func::construct_node(
              this->node_alloc(), *i));
          } else {
            // Only require basic exception safety here
            this->reserve_for_insert(size_ + distance);

            for (; i != j; ++i) {
              emplace_no_rehash_equiv(
                boost::unordered::detail::func::construct_node(
                  this->node_alloc(), *i));
            }
          }
        }

        template <class I>
        typename boost::unordered::detail::disable_if_forward<I, void>::type
        insert_range_equiv(I i, I j)
        {
          for (; i != j; ++i) {
            emplace_equiv(boost::unordered::detail::func::construct_node(
              this->node_alloc(), *i));
          }
        }

        ////////////////////////////////////////////////////////////////////////
        // Extract

        inline node_pointer extract_by_iterator_equiv(c_iterator n)
        {
          node_pointer p = n.p;
          bucket_iterator itb = n.itb;
          buckets_.extract_node(itb, p);
          --size_;
          return p;
        }

        ////////////////////////////////////////////////////////////////////////
        // Erase
        //
        // no throw

        template <class Key> std::size_t erase_key_equiv_impl(Key const& k)
        {
          std::size_t deleted_count = 0;

          bucket_iterator itb = buckets_.at(buckets_.position(this->hash(k)));
          node_pointer* pp = this->find_prev(k, itb);
          if (pp) {
            while (*pp && this->key_eq()(this->get_key(*pp), k)) {
              node_pointer p = *pp;
              *pp = (*pp)->next;

              this->delete_node(p);
              --size_;
              ++deleted_count;
            }

            if (!itb->next) {
              buckets_.unlink_bucket(itb);
            }
          }
          return deleted_count;
        }

        std::size_t erase_key_equiv(const_key_type& k)
        {
          return this->erase_key_equiv_impl(k);
        }

        ////////////////////////////////////////////////////////////////////////
        // fill_buckets

        void copy_buckets(table const& src, false_type)
        {
          BOOST_ASSERT(size_ == 0);

          this->reserve_for_insert(src.size_);

          iterator last = src.end();
          for (iterator pos = src.begin(); pos != last; ++pos) {
            value_type const& value = *pos;
            const_key_type& key = extractor::extract(value);
            std::size_t const key_hash = this->hash(key);

            bucket_iterator itb = buckets_.at(buckets_.position(key_hash));
            node_allocator_type alloc = this->node_alloc();
            node_tmp tmp(detail::func::construct_node(alloc, value), alloc);
            node_pointer hint = this->find_node_impl(key, itb);
            buckets_.insert_node_hint(itb, tmp.release(), hint);
            ++size_;
          }
        }

        void move_assign_buckets(table& src, false_type)
        {
          BOOST_ASSERT(size_ == 0);
          BOOST_ASSERT(max_load_ >= src.size_);

          iterator last = src.end();
          node_allocator_type alloc = this->node_alloc();

          for (iterator pos = src.begin(); pos != last; ++pos) {
            value_type value = boost::move(*pos);
            const_key_type& key = extractor::extract(value);
            std::size_t const key_hash = this->hash(key);

            bucket_iterator itb = buckets_.at(buckets_.position(key_hash));

            node_pointer hint = this->find_node_impl(key, itb);
            node_tmp tmp(
              detail::func::construct_node(alloc, boost::move(value)), alloc);

            buckets_.insert_node_hint(itb, tmp.release(), hint);
            ++size_;
          }
        }
      };

      //////////////////////////////////////////////////////////////////////////
      // Clear

      template <typename Types> inline void table<Types>::clear_impl()
      {
        bucket_iterator itb = buckets_.begin(), last = buckets_.end();
        for (; itb != last;) {
          bucket_iterator next_itb = itb;
          ++next_itb;
          node_pointer* pp = boost::addressof(itb->next);
          while (*pp) {
            node_pointer p = *pp;
            buckets_.extract_node_after(itb, pp);
            this->delete_node(p);
            --size_;
          }
          itb = next_itb;
        }
      }

      //////////////////////////////////////////////////////////////////////////
      // Reserve & Rehash

      // if hash function throws, basic exception safety
      // strong otherwise.
      template <typename Types>
      inline void table<Types>::rehash(std::size_t num_buckets)
      {
        std::size_t bc = (std::max)(num_buckets,
          static_cast<std::size_t>(1.0f + static_cast<float>(size_) / mlf_));

        if (bc <= buckets_.bucket_count()) {
          return;
        }

        this->rehash_impl(bc);
      }

      template <class Types>
      inline void table<Types>::reserve(std::size_t num_elements)
      {
        std::size_t const num_buckets = static_cast<std::size_t>(
          std::ceil(static_cast<float>(num_elements) / mlf_));

        this->rehash(num_buckets);
      }

      template <class Types>
      inline void table<Types>::reserve_for_insert(std::size_t num_elements)
      {
        if (num_elements > max_load_) {
          std::size_t const num_buckets = static_cast<std::size_t>(
            1.0f + std::ceil(static_cast<float>(num_elements) / mlf_));

          this->rehash_impl(num_buckets);
        }
      }

      template <class Types>
      inline void table<Types>::rehash_impl(std::size_t num_buckets)
      {
        bucket_array_type new_buckets(
          num_buckets, buckets_.get_node_allocator());

        BOOST_TRY
        {
          boost::unordered::detail::span<bucket_type> bspan = buckets_.raw();

          bucket_type* pos = bspan.data;
          std::size_t size = bspan.size;
          bucket_type* last = pos + size;

          for (; pos != last; ++pos) {
            bucket_type& b = *pos;
            for (node_pointer p = b.next; p;) {
              node_pointer next_p = p->next;
              transfer_node(p, b, new_buckets);
              p = next_p;
              b.next = p;
            }
          }
        }
        BOOST_CATCH(...)
        {
          for (bucket_iterator pos = new_buckets.begin();
               pos != new_buckets.end(); ++pos) {
            bucket_type& b = *pos;
            for (node_pointer p = b.next; p;) {
              node_pointer next_p = p->next;
              delete_node(p);
              --size_;
              p = next_p;
            }
          }
          buckets_.unlink_empty_buckets();
          BOOST_RETHROW;
        }
        BOOST_CATCH_END

        buckets_ = boost::move(new_buckets);
        recalculate_max_load();
      }

#if defined(BOOST_MSVC)
#pragma warning(pop)
#endif

      ////////////////////////////////////////////////////////////////////////
      // key extractors
      //
      // no throw
      //
      // 'extract_key' is called with the emplace parameters to return a
      // key if available or 'no_key' is one isn't and will need to be
      // constructed. This could be done by overloading the emplace
      // implementation
      // for the different cases, but that's a bit tricky on compilers without
      // variadic templates.

      template <typename Key, typename T> struct is_key
      {
        template <typename T2> static choice1::type test(T2 const&);
        static choice2::type test(Key const&);

        enum
        {
          value = sizeof(test(boost::unordered::detail::make<T>())) ==
                  sizeof(choice2::type)
        };

        typedef typename boost::detail::if_true<value>::BOOST_NESTED_TEMPLATE
          then<Key const&, no_key>::type type;
      };

      template <class ValueType> struct set_extractor
      {
        typedef ValueType value_type;
        typedef ValueType key_type;

        static key_type const& extract(value_type const& v) { return v; }

        static key_type const& extract(BOOST_UNORDERED_RV_REF(value_type) v)
        {
          return v;
        }

        static no_key extract() { return no_key(); }

        template <class Arg> static no_key extract(Arg const&)
        {
          return no_key();
        }

#if !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES)
        template <class Arg1, class Arg2, class... Args>
        static no_key extract(Arg1 const&, Arg2 const&, Args const&...)
        {
          return no_key();
        }
#else
        template <class Arg1, class Arg2>
        static no_key extract(Arg1 const&, Arg2 const&)
        {
          return no_key();
        }
#endif
      };

      template <class ValueType> struct map_extractor
      {
        typedef ValueType value_type;
        typedef typename boost::remove_const<typename boost::unordered::detail::
            pair_traits<ValueType>::first_type>::type key_type;

        static key_type const& extract(value_type const& v) { return v.first; }

        template <class Second>
        static key_type const& extract(std::pair<key_type, Second> const& v)
        {
          return v.first;
        }

        template <class Second>
        static key_type const& extract(
          std::pair<key_type const, Second> const& v)
        {
          return v.first;
        }

#if defined(BOOST_NO_CXX11_RVALUE_REFERENCES)
        template <class Second>
        static key_type const& extract(
          boost::rv<std::pair<key_type, Second> > const& v)
        {
          return v.first;
        }

        template <class Second>
        static key_type const& extract(
          boost::rv<std::pair<key_type const, Second> > const& v)
        {
          return v.first;
        }
#endif

        template <class Arg1>
        static key_type const& extract(key_type const& k, Arg1 const&)
        {
          return k;
        }

        static no_key extract() { return no_key(); }

        template <class Arg> static no_key extract(Arg const&)
        {
          return no_key();
        }

        template <class Arg1, class Arg2>
        static no_key extract(Arg1 const&, Arg2 const&)
        {
          return no_key();
        }

#if !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES)
        template <class Arg1, class Arg2, class Arg3, class... Args>
        static no_key extract(
          Arg1 const&, Arg2 const&, Arg3 const&, Args const&...)
        {
          return no_key();
        }
#endif

#if !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES)

#define BOOST_UNORDERED_KEY_FROM_TUPLE(namespace_)                             \
  template <typename T2>                                                       \
  static no_key extract(boost::unordered::piecewise_construct_t,               \
    namespace_ tuple<> const&, T2 const&)                                      \
  {                                                                            \
    return no_key();                                                           \
  }                                                                            \
                                                                               \
  template <typename T, typename T2>                                           \
  static typename is_key<key_type, T>::type extract(                           \
    boost::unordered::piecewise_construct_t, namespace_ tuple<T> const& k,     \
    T2 const&)                                                                 \
  {                                                                            \
    return typename is_key<key_type, T>::type(namespace_ get<0>(k));           \
  }

#else

#define BOOST_UNORDERED_KEY_FROM_TUPLE(namespace_)                             \
  static no_key extract(                                                       \
    boost::unordered::piecewise_construct_t, namespace_ tuple<> const&)        \
  {                                                                            \
    return no_key();                                                           \
  }                                                                            \
                                                                               \
  template <typename T>                                                        \
  static typename is_key<key_type, T>::type extract(                           \
    boost::unordered::piecewise_construct_t, namespace_ tuple<T> const& k)     \
  {                                                                            \
    return typename is_key<key_type, T>::type(namespace_ get<0>(k));           \
  }

#endif

        BOOST_UNORDERED_KEY_FROM_TUPLE(boost::)

#if BOOST_UNORDERED_TUPLE_ARGS
        BOOST_UNORDERED_KEY_FROM_TUPLE(std::)
#endif

#undef BOOST_UNORDERED_KEY_FROM_TUPLE
      };

      template <class Container, class Predicate>
      typename Container::size_type erase_if(Container& c, Predicate& pred)
      {
        typedef typename Container::size_type size_type;
        typedef typename Container::iterator iterator;

        size_type const size = c.size();

        for (iterator pos = c.begin(), last = c.end(); pos != last;) {
          if (pred(*pos)) {
            pos = c.erase(pos);
          } else {
            ++pos;
          }
        }

        return (size - c.size());
      }
    }
  }
}

#undef BOOST_UNORDERED_EMPLACE_TEMPLATE
#undef BOOST_UNORDERED_EMPLACE_ARGS
#undef BOOST_UNORDERED_EMPLACE_FORWARD

#endif