xref: /dports/science/py-scipy/scipy-1.7.1/scipy/_lib/boost/boost/container/devector.hpp

//////////////////////////////////////////////////////////////////////////////
//
// (C) Copyright Benedek Thaler 2015-2016
// (C) Copyright Ion Gaztanaga 2019-2020. 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)
//
// See http://www.boost.org/libs/container for documentation.
//
//////////////////////////////////////////////////////////////////////////////

#ifndef BOOST_CONTAINER_DEVECTOR_HPP
#define BOOST_CONTAINER_DEVECTOR_HPP

#include <boost/container/detail/config_begin.hpp>
#include <boost/container/detail/workaround.hpp>

//#include <algorithm>
#include <cstring> // memcpy

#include <boost/assert.hpp>
#include <boost/aligned_storage.hpp>

#include <boost/container/detail/copy_move_algo.hpp>
#include <boost/container/new_allocator.hpp> //new_allocator
#include <boost/container/allocator_traits.hpp> //allocator_traits
#include <boost/container/detail/algorithm.hpp> //equal()
#include <boost/container/throw_exception.hpp>
#include <boost/container/options.hpp>

#include <boost/container/detail/guards_dended.hpp>
#include <boost/container/detail/iterator.hpp>
#include <boost/container/detail/iterators.hpp>
#include <boost/container/detail/destroyers.hpp>
#include <boost/container/detail/min_max.hpp>
#include <boost/container/detail/next_capacity.hpp>
#include <boost/container/detail/alloc_helpers.hpp>

// move
#if defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES)
#include <boost/move/detail/fwd_macros.hpp>
#endif
#include <boost/move/detail/move_helpers.hpp>
#include <boost/move/adl_move_swap.hpp>
#include <boost/move/iterator.hpp>
#include <boost/move/traits.hpp>
#include <boost/move/utility_core.hpp>
#include <boost/move/detail/to_raw_pointer.hpp>
#include <boost/move/algo/detail/merge.hpp>

#include <boost/type_traits/is_nothrow_move_constructible.hpp>

//std
#if !defined(BOOST_NO_CXX11_HDR_INITIALIZER_LIST)
#include <initializer_list>   //for std::initializer_list
#endif

namespace boost {
namespace container {

#if !defined(BOOST_CONTAINER_DOXYGEN_INVOKED)

struct growth_factor_60;

template<class Options, class AllocatorSizeType>
struct get_devector_opt
{
   typedef devector_opt< typename default_if_void<typename Options::growth_factor_type, growth_factor_60>::type
                       , typename default_if_void<typename Options::stored_size_type, AllocatorSizeType>::type
                       > type;
};

template<class AllocatorSizeType>
struct get_devector_opt<void, AllocatorSizeType>
{
   typedef vector_opt<growth_factor_60, AllocatorSizeType> type;
};

#endif   //#if defined(BOOST_CONTAINER_DOXYGEN_INVOKED)

struct reserve_only_tag_t {};
//struct unsafe_uninitialized_tag_t {};

/**
 * A vector-like sequence container providing front and back operations
 * (e.g: `push_front`/`pop_front`/`push_back`/`pop_back`) with amortized constant complexity
 * and unsafe methods geared towards additional performance.
 *
 * Models the [SequenceContainer], [ReversibleContainer], and [AllocatorAwareContainer] concepts.
 *
 * **Requires**:
 *  - `T` shall be [MoveInsertable] into the devector.
 *  - `T` shall be [Erasable] from any `devector<T, allocator_type, GP>`.
 *  - `GrowthFactor`, and `Allocator` must model the concepts with the same names or be void.
 *
 * **Definition**: `T` is `NothrowConstructible` if it's either nothrow move constructible or
 * nothrow copy constructible.
 *
 * **Definition**: `T` is `NothrowAssignable` if it's either nothrow move assignable or
 * nothrow copy assignable.
 *
 * **Exceptions**: The exception specifications assume `T` is nothrow [Destructible].
 *
 * Most methods providing the strong exception guarantee assume `T` either has a move
 * constructor marked noexcept or is [CopyInsertable] into the devector. If it isn't true,
 * and the move constructor throws, the guarantee is waived and the effects are unspecified.
 *
 * In addition to the exceptions specified in the **Throws** clause, the following operations
 * of `T` can throw when any of the specified concept is required:
 *  - [DefaultInsertable][]: Default constructor
 *  - [MoveInsertable][]: Move constructor
 *  - [CopyInsertable][]: Copy constructor
 *  - [DefaultConstructible][]: Default constructor
 *  - [EmplaceConstructible][]: Constructor selected by the given arguments
 *  - [MoveAssignable][]: Move assignment operator
 *  - [CopyAssignable][]: Copy assignment operator
 *
 * Furthermore, not `noexcept` methods throws whatever the allocator throws
 * if memory allocation fails. Such methods also throw `length_error` if the capacity
 * exceeds `max_size()`.
 *
 * **Remark**: If a method invalidates some iterators, it also invalidates references
 * and pointers to the elements pointed by the invalidated iterators.
 *
 * **Policies**:
 *
 * @ref devector_growth_policy models the `GrowthFactor` concept.
 *
 * [SequenceContainer]: http://en.cppreference.com/w/cpp/concept/SequenceContainer
 * [ReversibleContainer]: http://en.cppreference.com/w/cpp/concept/ReversibleContainer
 * [AllocatorAwareContainer]: http://en.cppreference.com/w/cpp/concept/AllocatorAwareContainer
 * [DefaultInsertable]: http://en.cppreference.com/w/cpp/concept/DefaultInsertable
 * [MoveInsertable]: http://en.cppreference.com/w/cpp/concept/MoveInsertable
 * [CopyInsertable]: http://en.cppreference.com/w/cpp/concept/CopyInsertable
 * [Erasable]: http://en.cppreference.com/w/cpp/concept/Erasable
 * [DefaultConstructible]: http://en.cppreference.com/w/cpp/concept/DefaultConstructible
 * [Destructible]: http://en.cppreference.com/w/cpp/concept/Destructible
 * [EmplaceConstructible]: http://en.cppreference.com/w/cpp/concept/EmplaceConstructible
 * [MoveAssignable]: http://en.cppreference.com/w/cpp/concept/MoveAssignable
 * [CopyAssignable]: http://en.cppreference.com/w/cpp/concept/CopyAssignable
 */
template < typename T, class A BOOST_CONTAINER_DOCONLY(= void), class Options BOOST_CONTAINER_DOCONLY(= void)>
class devector
{
   #ifndef BOOST_CONTAINER_DOXYGEN_INVOKED
   typedef boost::container::allocator_traits
      <typename real_allocator<T, A>::type>                             allocator_traits_type;
   typedef typename allocator_traits_type::size_type                    alloc_size_type;
   typedef typename get_devector_opt<Options, alloc_size_type>::type    options_type;
   typedef typename options_type::growth_factor_type                    growth_factor_type;
   typedef typename options_type::stored_size_type                      stored_size_type;

   #endif // ifndef BOOST_CONTAINER_DOXYGEN_INVOKED

   public:
   // Standard Interface Types:
   typedef T                                                            value_type;
   typedef BOOST_CONTAINER_IMPDEF
      (typename real_allocator<T BOOST_MOVE_I A>::type)                 allocator_type;
   typedef allocator_type                                               stored_allocator_type;
   typedef typename   allocator_traits<allocator_type>::pointer         pointer;
   typedef typename   allocator_traits<allocator_type>::const_pointer   const_pointer;
   typedef typename   allocator_traits<allocator_type>::reference       reference;
   typedef typename   allocator_traits<allocator_type>::const_reference const_reference;
   typedef typename   allocator_traits<allocator_type>::size_type       size_type;
   typedef typename   allocator_traits<allocator_type>::difference_type difference_type;
   typedef pointer                                                      iterator;
   typedef const_pointer                                                const_iterator;
   typedef BOOST_CONTAINER_IMPDEF
      (boost::container::reverse_iterator<iterator>)                    reverse_iterator;
   typedef BOOST_CONTAINER_IMPDEF
      (boost::container::reverse_iterator<const_iterator>)              const_reverse_iterator;

   #ifndef BOOST_CONTAINER_DOXYGEN_INVOKED
   private:
   BOOST_COPYABLE_AND_MOVABLE(devector)

   // Guard to deallocate buffer on exception
   typedef typename detail::allocation_guard<allocator_type> allocation_guard;

   // Random access pseudo iterator always yielding to the same result
   typedef constant_iterator<T, difference_type> cvalue_iterator;

   #endif // ifndef BOOST_CONTAINER_DOXYGEN_INVOKED

   // Standard Interface
   public:
   // construct/copy/destroy

   /**
   * **Effects**: Constructs an empty devector.
   *
   * **Postcondition**: `empty() && front_free_capacity() == 0
   * && back_free_capacity() == 0`.
   *
   * **Complexity**: Constant.
   */
   devector() BOOST_NOEXCEPT
      : m_()
   {}

   /**
   * **Effects**: Constructs an empty devector, using the specified allocator.
   *
   * **Postcondition**: `empty() && front_free_capacity() == 0
   * && back_free_capacity() == 0`.
   *
   * **Complexity**: Constant.
   */
   explicit devector(const allocator_type& allocator) BOOST_NOEXCEPT
      : m_(allocator)
   {}

   /**
   * **Effects**: Constructs an empty devector, using the specified allocator
   * and reserves `n` slots as if `reserve(n)` was called.
   *
   * **Postcondition**: `empty() && front_free_capacity() == 0
   * && back_free_capacity() >= n`.
   *
   * **Exceptions**: Strong exception guarantee.
   *
   * **Complexity**: Constant.
   */
   devector(size_type n, reserve_only_tag_t, const allocator_type& allocator = allocator_type())
      : m_(allocator, this->allocate(n), 0u, 0u, n)
   {}

   /**
   * **Effects**: Constructs an empty devector, using the specified allocator
   * and reserves `front_cap + back_cap` slots as if `reserve_front(front_cap)` and
   * `reserve_back(back_cap)` was called.
   *
   * **Postcondition**: `empty() && front_free_capacity() == front_cap
   * && back_free_capacity() >= back_cap`.
   *
   * **Exceptions**: Strong exception guarantee.
   *
   * **Complexity**: Constant.
   */
   devector(size_type front_cap, size_type back_cap, reserve_only_tag_t, const allocator_type& allocator = allocator_type())
      : m_(allocator, this->allocate(front_cap + back_cap), front_cap, front_cap, front_cap + back_cap)
   {}

   /**
   * [DefaultInsertable]: http://en.cppreference.com/w/cpp/concept/DefaultInsertable
   *
   * **Effects**: Constructs a devector with `n` default-inserted elements using the specified allocator.
   *
   * **Requires**: `T` shall be [DefaultInsertable] into `*this`.
   *
   * **Postcondition**: `size() == n && front_free_capacity() == 0`.
   *
   * **Exceptions**: Strong exception guarantee.
   *
   * **Complexity**: Linear in `n`.
   */
   explicit devector(size_type n, const allocator_type& allocator = allocator_type())
      : m_(allocator, n ? allocate(n): pointer(), 0u, n, n)
   {
      // Cannot use construct_from_range/constant_iterator and copy_range,
      // because we are not allowed to default construct T
      allocation_guard buffer_guard(m_.buffer, m_.capacity, get_allocator_ref());
      detail::construction_guard<allocator_type> copy_guard(m_.buffer, get_allocator_ref());

      for (size_type i = 0; i < n; ++i)
      {
         this->alloc_construct(m_.buffer + i);
         copy_guard.extend();
      }

      copy_guard.release();
      buffer_guard.release();

      BOOST_ASSERT(invariants_ok());
   }

   /**
   * [CopyInsertable]: http://en.cppreference.com/w/cpp/concept/CopyInsertable
   *
   * **Effects**: Constructs a devector with `n` copies of `value`, using the specified allocator.
   *
   * **Requires**: `T` shall be [CopyInsertable] into `*this`.
   *
   * **Postcondition**: `size() == n && front_free_capacity() == 0`.
   *
   * **Exceptions**: Strong exception guarantee.
   *
   * **Complexity**: Linear in `n`.
   */
   devector(size_type n, const T& value, const allocator_type& allocator = allocator_type())
      : m_(allocator, n ? allocate(n): pointer(), 0u, n, n)
   {
      construct_from_range(cvalue_iterator(value, n), cvalue_iterator());
      BOOST_ASSERT(invariants_ok());
   }

   /**
   * **Effects**: Constructs a devector equal to the range `[first,last)`, using the specified allocator.
   *
   * **Requires**: `T` shall be [EmplaceConstructible] into `*this` from `*first`. If the specified
   * iterator does not meet the forward iterator requirements, `T` shall also be [MoveInsertable]
   * into `*this`.
   *
   * **Postcondition**: `size() == boost::container::iterator_distance(first, last)
   *
   * **Exceptions**: Strong exception guarantee.
   *
   * **Complexity**: Makes only `N` calls to the copy constructor of `T` (where `N` is the distance between `first`
   * and `last`), at most one allocation and no reallocations if iterators first and last are of forward,
   * bidirectional, or random access categories. It makes `O(N)` calls to the copy constructor of `T`
   * and `O(log(N)) reallocations if they are just input iterators.
   *
   * **Remarks**: Each iterator in the range `[first,last)` shall be dereferenced exactly once,
   * unless an exception is thrown.
   *
   * [EmplaceConstructible]: http://en.cppreference.com/w/cpp/concept/EmplaceConstructible
   * [MoveInsertable]: http://en.cppreference.com/w/cpp/concept/MoveInsertable
   */
   template <class InputIterator>
   devector(InputIterator first, InputIterator last, const allocator_type& allocator = allocator_type()
      //Input iterators
      BOOST_CONTAINER_DOCIGN(BOOST_MOVE_I typename dtl::disable_if_or
         < void
         BOOST_MOVE_I dtl::is_convertible<InputIterator BOOST_MOVE_I size_type>
         BOOST_MOVE_I dtl::is_not_input_iterator<InputIterator>
         >::type * = 0)
      )
      : m_(allocator, pointer(), 0u, 0u, 0u)
   {
      while (first != last) {
         this->emplace_back(*first++);
      }

      BOOST_ASSERT(invariants_ok());
   }

   #ifndef BOOST_CONTAINER_DOXYGEN_INVOKED

   template <class ForwardIterator>
   devector(ForwardIterator first, ForwardIterator last, const allocator_type& allocator = allocator_type()
      //Other iterators
      BOOST_CONTAINER_DOCIGN(BOOST_MOVE_I typename dtl::disable_if_or
         < void
         BOOST_MOVE_I dtl::is_convertible<ForwardIterator BOOST_MOVE_I size_type>
         BOOST_MOVE_I dtl::is_input_iterator<ForwardIterator>
         >::type * = 0)
      )
      : m_(allocator, pointer(), 0u, 0u, 0u)
   {
      const size_type n = boost::container::iterator_distance(first, last);
      m_.buffer = n ? allocate(n) : pointer();
      m_.front_idx = 0u;
      m_.set_back_idx(n);
      m_.set_capacity(n);
      construct_from_range(first, last);
      BOOST_ASSERT(invariants_ok());
   }

   #endif // ifndef BOOST_CONTAINER_DOXYGEN_INVOKED

   /**
   * [CopyInsertable]: http://en.cppreference.com/w/cpp/concept/CopyInsertable
   *
   * **Effects**: Copy constructs a devector.
   *
   * **Requires**: `T` shall be [CopyInsertable] into `*this`.
   *
   * **Postcondition**: `this->size() == x.size() && front_free_capacity() == 0`.
   *
   * **Exceptions**: Strong exception guarantee.
   *
   * **Complexity**: Linear in the size of `x`.
   */
   devector(const devector& x)
      : m_( allocator_traits_type::select_on_container_copy_construction(x.get_allocator_ref())
          , pointer(), 0u, 0u, 0u)
   {
      const size_type n = x.size();
      m_.buffer = n ? allocate(n) : pointer();
      m_.front_idx = 0u;
      //this->allocate(n) will take care of overflows
      m_.set_back_idx(n);
      m_.set_capacity(n);
      this->construct_from_range(x.begin(), x.end());
      BOOST_ASSERT(invariants_ok());
   }

   /**
   * [CopyInsertable]: http://en.cppreference.com/w/cpp/concept/CopyInsertable
   *
   * **Effects**: Copy constructs a devector, using the specified allocator.
   *
   * **Requires**: `T` shall be [CopyInsertable] into `*this`.
   *
   * **Postcondition**: `this->size() == x.size() && front_free_capacity() == 0`.
   *
   * **Exceptions**: Strong exception guarantee.
   *
   * **Complexity**: Linear in the size of `x`.
   */
   devector(const devector& x, const allocator_type& allocator)
      : m_(allocator, pointer(), 0u, 0u, 0u)
   {
      const size_type n = x.size();
      m_.buffer = n ? this->allocate(n) : pointer();
      m_.front_idx = 0u;
      //this->allocate(n) will take care of overflows
      m_.set_back_idx(n);
      m_.set_capacity(n);
      this->construct_from_range(x.begin(), x.end());
      BOOST_ASSERT(invariants_ok());
   }

   /**
   * **Effects**: Moves `rhs`'s resources to `*this`.
   *
   * **Throws**: Nothing.
   *
   * **Postcondition**: `rhs` is left in an unspecified but valid state.
   *
   * **Exceptions**: Strong exception guarantee if not `noexcept`.
   *
   * **Complexity**: Constant.
   */
   devector(BOOST_RV_REF(devector) rhs) BOOST_NOEXCEPT_OR_NOTHROW
      : m_(::boost::move(rhs.get_allocator_ref()), rhs.m_.buffer, rhs.m_.front_idx, rhs.m_.back_idx, rhs.capacity())
   {
      // buffer is already acquired, reset rhs
      rhs.m_.capacity = 0u;
      rhs.m_.buffer = pointer();
      rhs.m_.front_idx = 0;
      rhs.m_.back_idx = 0;
      BOOST_ASSERT(    invariants_ok());
      BOOST_ASSERT(rhs.invariants_ok());
   }

   /**
   * **Effects**: Moves `rhs`'s resources to `*this`, using the specified allocator.
   *
   * **Throws**: If allocation or T's move constructor throws.
   *
   * **Postcondition**: `rhs` is left in an unspecified but valid state.
   *
   * **Exceptions**: Strong exception guarantee if not `noexcept`.
   *
   * **Complexity**: Linear if allocator != rhs.get_allocator(), otherwise constant.
   */
   devector(BOOST_RV_REF(devector) rhs, const allocator_type& allocator)
      : m_(allocator, rhs.m_.buffer, rhs.m_.front_idx, rhs.m_.back_idx, rhs.capacity())
   {
      // TODO should move elems-by-elems if the two allocators differ
      // buffer is already acquired, reset rhs
      rhs.m_.capacity = 0u;
      rhs.m_.buffer = pointer();
      rhs.m_.front_idx = 0;
      rhs.m_.back_idx = 0;
      BOOST_ASSERT(    invariants_ok());
      BOOST_ASSERT(rhs.invariants_ok());
   }

   #if !defined(BOOST_NO_CXX11_HDR_INITIALIZER_LIST)
   /**
   * **Equivalent to**: `devector(il.begin(), il.end())` or `devector(il.begin(), il.end(), allocator)`.
   */
   devector(const std::initializer_list<T>& il, const allocator_type& allocator = allocator_type())
      : devector(il.begin(), il.end(), allocator)
   {}
   #endif

  /**
   * **Effects**: Destroys the devector. All stored values are destroyed and
   * used memory, if any, deallocated.
   *
   * **Complexity**: Linear in the size of `*this`.
   */
  ~devector() BOOST_NOEXCEPT
  {
    destroy_elements(m_.buffer + m_.front_idx, m_.buffer + m_.back_idx);
    deallocate_buffer();
  }

  /**
   * **Effects**: Copies elements of `x` to `*this`. Previously
   * held elements get copy assigned to or destroyed.
   *
   * **Requires**: `T` shall be [CopyInsertable] into `*this`.
   *
   * **Postcondition**: `this->size() == x.size()`, the elements of
   * `*this` are copies of elements in `x` in the same order.
   *
   * **Returns**: `*this`.
   *
   * **Exceptions**: Strong exception guarantee if `T` is `NothrowConstructible`
   * and the allocator is allowed to be propagated
   * ([propagate_on_container_copy_assignment] is true),
   * Basic exception guarantee otherwise.
   *
   * **Complexity**: Linear in the size of `x` and `*this`.
   *
   * [CopyInsertable]: http://en.cppreference.com/w/cpp/concept/CopyInsertable
   * [propagate_on_container_copy_assignment]: http://en.cppreference.com/w/cpp/memory/allocator_traits
   */

   BOOST_CONTAINER_FORCEINLINE devector& operator=(BOOST_COPY_ASSIGN_REF(devector) rhs)
   {
      const devector &x = rhs;
      if (this == &x) { return *this; } // skip self

      BOOST_IF_CONSTEXPR(allocator_traits_type::propagate_on_container_copy_assignment::value)
      {
         allocator_type &this_alloc = this->get_allocator_ref();
         const allocator_type &other_alloc = x.get_allocator_ref();
         if (this_alloc != other_alloc)
         {
            // new allocator cannot free existing storage
            this->clear();
            this->deallocate_buffer();
            m_.capacity = 0u;
            m_.buffer = pointer();
         }

         this_alloc = other_alloc;
      }

      size_type n = x.size();
      if (capacity() >= n)
      {
         this->overwrite_buffer(x.begin(), x.end());
      }
      else
      {
         this->allocate_and_copy_range(x.begin(), x.end());
      }

      BOOST_ASSERT(invariants_ok());

      return *this;
   }

   /**
   * [MoveInsertable]: http://en.cppreference.com/w/cpp/concept/MoveInsertable
   *
   * **Effects**: Moves elements of `x` to `*this`. Previously
   * held elements get move/copy assigned to or destroyed.
   *
   * **Requires**: `T` shall be [MoveInsertable] into `*this`.
   *
   * **Postcondition**: `x` is left in an unspecified but valid state.
   *
   * **Returns**: `*this`.
   *
   * **Exceptions**: Basic exception guarantee if not `noexcept`.
   *
   * **Complexity**: Constant if allocator_traits_type::
   *  propagate_on_container_move_assignment is true or
   *  this->get>allocator() == x.get_allocator(). Linear otherwise.
   */
   devector& operator=(BOOST_RV_REF(devector) x)
      BOOST_NOEXCEPT_IF(allocator_traits_type::propagate_on_container_move_assignment::value
                        || allocator_traits_type::is_always_equal::value)
   {
      BOOST_CONSTEXPR_OR_CONST bool copy_alloc = allocator_traits_type::propagate_on_container_move_assignment::value;

      BOOST_IF_CONSTEXPR (copy_alloc || get_allocator_ref() == x.get_allocator_ref())
      {
         this->clear();
         this->deallocate_buffer();

         if (copy_alloc)
         {
            this->get_allocator_ref() = boost::move(x.get_allocator_ref());
         }

         m_.capacity = x.m_.capacity;
         m_.buffer = x.m_.buffer;
         m_.front_idx = x.m_.front_idx;
         m_.back_idx = x.m_.back_idx;

         // leave x in valid state
         x.m_.capacity = 0u;
         x.m_.buffer = pointer();
         x.m_.back_idx = x.m_.front_idx = 0;
      }
      else
      {
         // if the allocator shouldn't be copied and they do not compare equal
         // we can't steal memory.

         move_iterator<iterator> xbegin = boost::make_move_iterator(x.begin());
         move_iterator<iterator> xend = boost::make_move_iterator(x.end());

         if (copy_alloc)
         {
            get_allocator_ref() = boost::move(x.get_allocator_ref());
         }

         if (capacity() >= x.size())
         {
            overwrite_buffer(xbegin, xend);
         }
         else
         {
            allocate_and_copy_range(xbegin, xend);
         }
      }

      BOOST_ASSERT(invariants_ok());

      return *this;
   }

   #if !defined(BOOST_NO_CXX11_HDR_INITIALIZER_LIST)
   /**
   * **Effects**: Copies elements of `il` to `*this`. Previously
   * held elements get copy assigned to or destroyed.
   *
   * **Requires**: `T` shall be [CopyInsertable] into `*this` and [CopyAssignable].
   *
   * **Postcondition**: `this->size() == il.size()`, the elements of
   * `*this` are copies of elements in `il` in the same order.
   *
   * **Exceptions**: Strong exception guarantee if `T` is nothrow copy assignable
   * from `T` and `NothrowConstructible`, Basic exception guarantee otherwise.
   *
   * **Returns**: `*this`.
   *
   * **Complexity**: Linear in the size of `il` and `*this`.
   *
   * [CopyInsertable]: http://en.cppreference.com/w/cpp/concept/CopyInsertable
   * [CopyAssignable]: http://en.cppreference.com/w/cpp/concept/CopyAssignable
   */
   devector& operator=(std::initializer_list<T> il)
   {
      assign(il.begin(), il.end());
      return *this;
   }
   #endif

   /**
   * **Effects**: Replaces elements of `*this` with a copy of `[first,last)`.
   * Previously held elements get copy assigned to or destroyed.
   *
   * **Requires**: `T` shall be [EmplaceConstructible] from `*first`. If the specified iterator
   * does not meet the forward iterator requirements, `T` shall be also [MoveInsertable] into `*this`.
   *
   * **Precondition**: `first` and `last` are not iterators into `*this`.
   *
   * **Postcondition**: `size() == N`, where `N` is the distance between `first` and `last`.
   *
   * **Exceptions**: Strong exception guarantee if `T` is nothrow copy assignable
   * from `*first` and `NothrowConstructible`, Basic exception guarantee otherwise.
   *
   * **Complexity**: Linear in the distance between `first` and `last`.
   * Makes a single reallocation at most if the iterators `first` and `last`
   * are of forward, bidirectional, or random access categories. It makes
   * `O(log(N))` reallocations if they are just input iterators.
   *
   * **Remarks**: Each iterator in the range `[first,last)` shall be dereferenced exactly once,
   * unless an exception is thrown.
   *
   * [EmplaceConstructible]: http://en.cppreference.com/w/cpp/concept/EmplaceConstructible
   * [MoveInsertable]: http://en.cppreference.com/w/cpp/concept/MoveInsertable
   */
   template <class InputIterator>
   void assign(InputIterator first, InputIterator last
      //Input iterators
      BOOST_CONTAINER_DOCIGN(BOOST_MOVE_I typename dtl::disable_if_or
         < void
         BOOST_MOVE_I dtl::is_convertible<InputIterator BOOST_MOVE_I size_type>
         BOOST_MOVE_I dtl::is_not_input_iterator<InputIterator>
         >::type * = 0)
      )
   {
      first = overwrite_buffer_impl(first, last, dtl::false_());
      while (first != last)
      {
         this->emplace_back(*first++);
      }
   }

   #ifndef BOOST_CONTAINER_DOXYGEN_INVOKED

   template <class ForwardIterator>
   void assign(ForwardIterator first, ForwardIterator last
      //Other iterators
      BOOST_CONTAINER_DOCIGN(BOOST_MOVE_I typename dtl::disable_if_or
         < void
         BOOST_MOVE_I dtl::is_convertible<ForwardIterator BOOST_MOVE_I size_type>
         BOOST_MOVE_I dtl::is_input_iterator<ForwardIterator>
         >::type * = 0)
      )
   {
      const size_type n = boost::container::iterator_distance(first, last);

      if (capacity() >= n)
      {
         overwrite_buffer(first, last);
      }
      else
      {
         allocate_and_copy_range(first, last);
      }

      BOOST_ASSERT(invariants_ok());
   }

   #endif // ifndef BOOST_CONTAINER_DOXYGEN_INVOKED

  /**
   * **Effects**: Replaces elements of `*this` with `n` copies of `u`.
   * Previously held elements get copy assigned to or destroyed.
   *
   * **Requires**: `T` shall be [CopyInsertable] into `*this` and
   * [CopyAssignable].
   *
   * **Precondition**: `u` is not a reference into `*this`.
   *
   * **Postcondition**: `size() == n` and the elements of
   * `*this` are copies of `u`.
   *
   * **Exceptions**: Strong exception guarantee if `T` is nothrow copy assignable
   * from `u` and `NothrowConstructible`, Basic exception guarantee otherwise.
   *
   * **Complexity**: Linear in `n` and the size of `*this`.
   *
   * [CopyInsertable]: http://en.cppreference.com/w/cpp/concept/CopyInsertable
   * [CopyAssignable]: http://en.cppreference.com/w/cpp/concept/CopyAssignable
   */
  void assign(size_type n, const T& u)
  {
    cvalue_iterator first(u, n);
    cvalue_iterator last;

    assign(first, last);
  }

   #if !defined(BOOST_NO_CXX11_HDR_INITIALIZER_LIST)
   /** **Equivalent to**: `assign(il.begin(), il.end())`. */
   void assign(std::initializer_list<T> il)
   {
      assign(il.begin(), il.end());
   }
   #endif

  /**
   * **Returns**: A copy of the allocator associated with the container.
   *
   * **Complexity**: Constant.
   */
  allocator_type get_allocator() const BOOST_NOEXCEPT
  {
    return static_cast<const allocator_type&>(m_);
  }

  const allocator_type &get_stored_allocator() const BOOST_NOEXCEPT
  {
    return static_cast<const allocator_type&>(m_);
  }

  allocator_type &get_stored_allocator() BOOST_NOEXCEPT
  {
    return static_cast<allocator_type&>(m_);
  }

  // iterators

  /**
   * **Returns**: A iterator pointing to the first element in the devector,
   * or the past the end iterator if the devector is empty.
   *
   * **Complexity**: Constant.
   */
  iterator begin() BOOST_NOEXCEPT
  {
    return m_.buffer + m_.front_idx;
  }

  /**
   * **Returns**: A constant iterator pointing to the first element in the devector,
   * or the past the end iterator if the devector is empty.
   *
   * **Complexity**: Constant.
   */
  const_iterator begin() const BOOST_NOEXCEPT
  {
    return m_.buffer + m_.front_idx;
  }

  /**
   * **Returns**: An iterator pointing past the last element of the container.
   *
   * **Complexity**: Constant.
   */
  iterator end() BOOST_NOEXCEPT
  {
    return m_.buffer + m_.back_idx;
  }

  /**
   * **Returns**: A constant iterator pointing past the last element of the container.
   *
   * **Complexity**: Constant.
   */
  const_iterator end() const BOOST_NOEXCEPT
  {
    return m_.buffer + m_.back_idx;
  }

  /**
   * **Returns**: A reverse iterator pointing to the first element in the reversed devector,
   * or the reverse past the end iterator if the devector is empty.
   *
   * **Complexity**: Constant.
   */
  reverse_iterator rbegin() BOOST_NOEXCEPT
  {
    return reverse_iterator(m_.buffer + m_.back_idx);
  }

  /**
   * **Returns**: A constant reverse iterator
   * pointing to the first element in the reversed devector,
   * or the reverse past the end iterator if the devector is empty.
   *
   * **Complexity**: Constant.
   */
  const_reverse_iterator rbegin() const BOOST_NOEXCEPT
  {
    return const_reverse_iterator(m_.buffer + m_.back_idx);
  }

  /**
   * **Returns**: A reverse iterator pointing past the last element in the
   * reversed container, or to the beginning of the reversed container if it's empty.
   *
   * **Complexity**: Constant.
   */
  reverse_iterator rend() BOOST_NOEXCEPT
  {
    return reverse_iterator(m_.buffer + m_.front_idx);
  }

  /**
   * **Returns**: A constant reverse iterator pointing past the last element in the
   * reversed container, or to the beginning of the reversed container if it's empty.
   *
   * **Complexity**: Constant.
   */
  const_reverse_iterator rend() const BOOST_NOEXCEPT
  {
    return const_reverse_iterator(m_.buffer + m_.front_idx);
  }

  /**
   * **Returns**: A constant iterator pointing to the first element in the devector,
   * or the past the end iterator if the devector is empty.
   *
   * **Complexity**: Constant.
   */
  const_iterator cbegin() const BOOST_NOEXCEPT
  {
    return m_.buffer + m_.front_idx;
  }

  /**
   * **Returns**: A constant iterator pointing past the last element of the container.
   *
   * **Complexity**: Constant.
   */
  const_iterator cend() const BOOST_NOEXCEPT
  {
    return m_.buffer + m_.back_idx;
  }

  /**
   * **Returns**: A constant reverse iterator
   * pointing to the first element in the reversed devector,
   * or the reverse past the end iterator if the devector is empty.
   *
   * **Complexity**: Constant.
   */
  const_reverse_iterator crbegin() const BOOST_NOEXCEPT
  {
    return const_reverse_iterator(m_.buffer + m_.back_idx);
  }

  /**
   * **Returns**: A constant reverse iterator pointing past the last element in the
   * reversed container, or to the beginning of the reversed container if it's empty.
   *
   * **Complexity**: Constant.
   */
  const_reverse_iterator crend() const BOOST_NOEXCEPT
  {
    return const_reverse_iterator(m_.buffer + m_.front_idx);
  }

  // capacity

  /**
   * **Returns**: True, if `size() == 0`, false otherwise.
   *
   * **Complexity**: Constant.
   */
  bool empty() const BOOST_NOEXCEPT
  {
    return m_.front_idx == m_.back_idx;
  }

  /**
   * **Returns**: The number of elements the devector contains.
   *
   * **Complexity**: Constant.
   */
  size_type size() const BOOST_NOEXCEPT
  {
    return m_.back_idx - m_.front_idx;
  }

  /**
   * **Returns**: The maximum number of elements the devector could possibly hold.
   *
   * **Complexity**: Constant.
   */
  size_type max_size() const BOOST_NOEXCEPT
  {
    size_type alloc_max = allocator_traits_type::max_size(get_allocator_ref());
    size_type size_type_max = (size_type)-1;
    return (alloc_max <= size_type_max) ? size_type(alloc_max) : size_type_max;
  }

  /**
   * **Returns**: The total number of elements that the devector can hold without requiring reallocation.
   *
   * **Complexity**: Constant.
   */
  size_type capacity() const BOOST_NOEXCEPT
  {
    return m_.capacity;
  }

  /**
   * **Returns**: The total number of elements that can be pushed to the front of the
   * devector without requiring reallocation.
   *
   * **Complexity**: Constant.
   */
  size_type front_free_capacity() const BOOST_NOEXCEPT
  {
    return m_.front_idx;
  }

  /**
   * **Returns**: The total number of elements that can be pushed to the back of the
   * devector without requiring reallocation.
   *
   * **Complexity**: Constant.
   */
  size_type back_free_capacity() const BOOST_NOEXCEPT
  {
    return m_.capacity - m_.back_idx;
  }

  /** **Equivalent to**: `resize_back(sz)` */
  void resize(size_type sz) { resize_back(sz); }

  /** **Equivalent to**: `resize_back(sz, c)` */
  void resize(size_type sz, const T& c) { resize_back(sz, c); }

  /**
   * **Effects**: If `sz` is greater than the size of `*this`,
   * additional value-initialized elements are inserted
   * to the front. Invalidates iterators if reallocation is needed.
   * If `sz` is smaller than than the size of `*this`,
   * elements are popped from the front.
   *
   * **Requires**: T shall be [MoveInsertable] into *this and [DefaultConstructible].
   *
   * **Postcondition**: `sz == size()`.
   *
   * **Exceptions**: Strong exception guarantee.
   *
   * **Complexity**: Linear in the size of `*this` and `sz`.
   *
   * [MoveInsertable]: http://en.cppreference.com/w/cpp/concept/MoveInsertable
   * [DefaultConstructible]: http://en.cppreference.com/w/cpp/concept/DefaultConstructible
   */
  void resize_front(size_type sz)
  {
    resize_front_impl(sz);
    BOOST_ASSERT(invariants_ok());
  }

  /**
   * [CopyInsertable]: http://en.cppreference.com/w/cpp/concept/CopyInsertable
   *
   * **Effects**: If `sz` is greater than the size of `*this`,
   * copies of `c` are inserted to the front.
   * Invalidates iterators if reallocation is needed.
   * If `sz` is smaller than than the size of `*this`,
   * elements are popped from the front.
   *
   * **Postcondition**: `sz == size()`.
   *
   * **Requires**: `T` shall be [CopyInsertable] into `*this`.
   *
   * **Exceptions**: Strong exception guarantee.
   *
   * **Complexity**: Linear in the size of `*this` and `sz`.
   */
  void resize_front(size_type sz, const T& c)
  {
    resize_front_impl(sz, c);
    BOOST_ASSERT(invariants_ok());
  }

  /**
   * **Effects**: If `sz` is greater than the size of `*this`,
   * additional value-initialized elements are inserted
   * to the back. Invalidates iterators if reallocation is needed.
   * If `sz` is smaller than than the size of `*this`,
   * elements are popped from the back.
   *
   * **Requires**: T shall be [MoveInsertable] into *this and [DefaultConstructible].
   *
   * **Postcondition**: `sz == size()`.
   *
   * **Exceptions**: Strong exception guarantee.
   *
   * **Complexity**: Linear in the size of `*this` and `sz`.
   *
   * [MoveInsertable]: http://en.cppreference.com/w/cpp/concept/MoveInsertable
   * [DefaultConstructible]: http://en.cppreference.com/w/cpp/concept/DefaultConstructible
   */
  void resize_back(size_type sz)
  {
    resize_back_impl(sz);
    BOOST_ASSERT(invariants_ok());
  }

  /**
   * [CopyInsertable]: http://en.cppreference.com/w/cpp/concept/CopyInsertable
   *
   * **Effects**: If `sz` is greater than the size of `*this`,
   * copies of `c` are inserted to the back.
   * If `sz` is smaller than than the size of `*this`,
   * elements are popped from the back.
   *
   * **Postcondition**: `sz == size()`.
   *
   * **Requires**: `T` shall be [CopyInsertable] into `*this`.
   *
   * **Exceptions**: Strong exception guarantee.
   *
   * **Complexity**: Linear in the size of `*this` and `sz`.
   */
  void resize_back(size_type sz, const T& c)
  {
    resize_back_impl(sz, c);
    BOOST_ASSERT(invariants_ok());
  }

  // unsafe uninitialized resize methods

  /**
   * **Unsafe method**, use with care.
   *
   * **Effects**: Changes the size of the devector without properly
   * initializing the extra or destroying the superfluous elements.
   * If `n < size()`, elements are removed from the front without
   * getting destroyed; if `n > size()`, uninitialized elements are added
   * before the first element at the front.
   * Invalidates iterators if reallocation is needed.
   *
   * **Postcondition**: `size() == n`.
   *
   * **Exceptions**: Strong exception guarantee.
   *
   * **Complexity**: Linear in `size()` if `capacity() < n`, constant otherwise.
   *
   * **Remarks**: The devector does not keep track of initialization of the elements:
   * Elements without a trivial destructor must be manually destroyed before shrinking,
   * elements without a trivial constructor must be initialized after growing.
   */
/*
  void unsafe_uninitialized_resize_front(size_type n)
  {
    if (n > size())
    {
      unsafe_uninitialized_grow_front(n);
    }
    else
    {
      unsafe_uninitialized_shrink_front(n);
    }
  }
*/
  /**
   * **Unsafe method**, use with care.
   *
   * **Effects**: Changes the size of the devector without properly
   * initializing the extra or destroying the superfluous elements.
   * If `n < size()`, elements are removed from the back without
   * getting destroyed; if `n > size()`, uninitialized elements are added
   * after the last element at the back.
   * Invalidates iterators if reallocation is needed.
   *
   * **Postcondition**: `size() == n`.
   *
   * **Exceptions**: Strong exception guarantee.
   *
   * **Complexity**: Linear in `size()` if `capacity() < n`, constant otherwise.
   *
   * **Remarks**: The devector does not keep track of initialization of the elements:
   * Elements without a trivial destructor must be manually destroyed before shrinking,
   * elements without a trivial constructor must be initialized after growing.
   */
/*
  void unsafe_uninitialized_resize_back(size_type n)
  {
    if (n > size())
    {
      unsafe_uninitialized_grow_back(n);
    }
    else
    {
      unsafe_uninitialized_shrink_back(n);
    }
  }
*/
  // reserve promise:
  // after reserve_[front,back](n), n - size() push_[front,back] will not allocate

  /** **Equivalent to**: `reserve_back(new_capacity)` */
  void reserve(size_type new_capacity) { reserve_back(new_capacity); }

  /**
   * [MoveInsertable]: http://en.cppreference.com/w/cpp/concept/MoveInsertable
   *
   * **Effects**: Ensures that `n` elements can be pushed to the front
   * without requiring reallocation, where `n` is `new_capacity - size()`,
   * if `n` is positive. Otherwise, there are no effects.
   * Invalidates iterators if reallocation is needed.
   *
   * **Requires**: `T` shall be [MoveInsertable] into `*this`.
   *
   * **Complexity**: Linear in the size of *this.
   *
   * **Exceptions**: Strong exception guarantee.
   *
   * **Throws**: `length_error` if `new_capacity > max_size()`.
   */
  void reserve_front(size_type new_capacity)
  {
    if (front_capacity() >= new_capacity) { return; }

    reallocate_at(new_capacity + back_free_capacity(), new_capacity - size());

    BOOST_ASSERT(invariants_ok());
  }

  /**
   * [MoveInsertable]: http://en.cppreference.com/w/cpp/concept/MoveInsertable
   *
   * **Effects**: Ensures that `n` elements can be pushed to the back
   * without requiring reallocation, where `n` is `new_capacity - size()`,
   * if `n` is positive. Otherwise, there are no effects.
   * Invalidates iterators if reallocation is needed.
   *
   * **Requires**: `T` shall be [MoveInsertable] into `*this`.
   *
   * **Complexity**: Linear in the size of *this.
   *
   * **Exceptions**: Strong exception guarantee.
   *
   * **Throws**: length_error if `new_capacity > max_size()`.
   */
  void reserve_back(size_type new_capacity)
  {
    if (back_capacity() >= new_capacity) { return; }

    reallocate_at(new_capacity + front_free_capacity(), m_.front_idx);

    BOOST_ASSERT(invariants_ok());
  }


  /**
   * [MoveInsertable]: http://en.cppreference.com/w/cpp/concept/MoveInsertable
   *
   * **Effects**: Reduces `capacity()` to `size()`. Invalidates iterators.
   *
   * **Requires**: `T` shall be [MoveInsertable] into `*this`.
   *
   * **Exceptions**: Strong exception guarantee.
   *
   * **Complexity**: Linear in the size of *this.
   */
  void shrink_to_fit()
  {
      if(this->front_capacity() || this->back_capacity())
         this->reallocate_at(size(), 0);
  }

  // element access:

  /**
   * **Returns**: A reference to the `n`th element in the devector.
   *
   * **Precondition**: `n < size()`.
   *
   * **Complexity**: Constant.
   */
  reference operator[](size_type n) BOOST_NOEXCEPT
  {
    BOOST_ASSERT(n < size());

    return *(begin() + n);
  }

  /**
   * **Returns**: A constant reference to the `n`th element in the devector.
   *
   * **Precondition**: `n < size()`.
   *
   * **Complexity**: Constant.
   */
  const_reference operator[](size_type n) const BOOST_NOEXCEPT
  {
    BOOST_ASSERT(n < size());

    return *(begin() + n);
  }

   /**
   * **Returns**: A reference to the `n`th element in the devector.
   *
   * **Throws**: `std::out_of_range`, if `n >= size()`.
   *
   * **Complexity**: Constant.
   */
   reference at(size_type n)
   {
      if (size() <= n)
         throw_out_of_range("devector::at out of range");
      return (*this)[n];
   }

   /**
   * **Returns**: A constant reference to the `n`th element in the devector.
   *
   * **Throws**: `std::out_of_range`, if `n >= size()`.
   *
   * **Complexity**: Constant.
   */
   const_reference at(size_type n) const
   {
      if (size() <= n)
         throw_out_of_range("devector::at out of range");
      return (*this)[n];
   }

   /**
   * **Returns**: A reference to the first element in the devector.
   *
   * **Precondition**: `!empty()`.
   *
   * **Complexity**: Constant.
   */
   reference front() BOOST_NOEXCEPT
   {
      BOOST_ASSERT(!empty());

      return *(m_.buffer + m_.front_idx);
   }

   /**
   * **Returns**: A constant reference to the first element in the devector.
   *
   * **Precondition**: `!empty()`.
   *
   * **Complexity**: Constant.
   */
   const_reference front() const BOOST_NOEXCEPT
   {
      BOOST_ASSERT(!empty());

      return *(m_.buffer + m_.front_idx);
   }

   /**
   * **Returns**: A reference to the last element in the devector.
   *
   * **Precondition**: `!empty()`.
   *
   * **Complexity**: Constant.
   */
   reference back() BOOST_NOEXCEPT
   {
      BOOST_ASSERT(!empty());

      return *(m_.buffer + m_.back_idx -1);
   }

   /**
   * **Returns**: A constant reference to the last element in the devector.
   *
   * **Precondition**: `!empty()`.
   *
   * **Complexity**: Constant.
   */
   const_reference back() const BOOST_NOEXCEPT
   {
      BOOST_ASSERT(!empty());

      return *(m_.buffer + m_.back_idx -1);
   }

   /**
   * **Returns**: A pointer to the underlying array serving as element storage.
   * The range `[data(); data() + size())` is always valid. For a non-empty devector,
   * `data() == &front()`.
   *
   * **Complexity**: Constant.
   */
   T* data() BOOST_NOEXCEPT
   {
      return boost::movelib::to_raw_pointer(m_.buffer) + m_.front_idx;
   }

   /**
   * **Returns**: A constant pointer to the underlying array serving as element storage.
   * The range `[data(); data() + size())` is always valid. For a non-empty devector,
   * `data() == &front()`.
   *
   * **Complexity**: Constant.
   */
   const T* data() const BOOST_NOEXCEPT
   {
      return boost::movelib::to_raw_pointer(m_.buffer) + m_.front_idx;
   }

   // modifiers:

   /**
   * **Effects**: Pushes a new element to the front of the devector.
   * The element is constructed in-place, using the perfect forwarded `args`
   * as constructor arguments. Invalidates iterators if reallocation is needed.
   * (`front_free_capacity() == 0`)
   *
   * **Requires**: `T` shall be [EmplaceConstructible] from `args` and [MoveInsertable] into `*this`.
   *
   * **Exceptions**: Strong exception guarantee.
   *
   * **Complexity**: Amortized constant in the size of `*this`.
   * (Constant, if `front_free_capacity() > 0`)
   *
   * [EmplaceConstructible]: http://en.cppreference.com/w/cpp/concept/EmplaceConstructible
   * [MoveInsertable]: http://en.cppreference.com/w/cpp/concept/MoveInsertable
   */
   #if !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES) || defined(BOOST_CONTAINER_DOXYGEN_INVOKED)
   template <class... Args>
   void emplace_front(Args&&... args)
   {
      if (front_free_capacity()) // fast path
      {
         this->alloc_construct(m_.buffer + m_.front_idx - 1, boost::forward<Args>(args)...);
         --m_.front_idx;
      }
      else
      {
         this->emplace_reallocating_slow_path(true, 0, boost::forward<Args>(args)...);
      }

      BOOST_ASSERT(invariants_ok());
   }

   #else //!defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES) || defined(BOOST_CONTAINER_DOXYGEN_INVOKED)

   #define BOOST_CONTAINER_DEVECTOR_EMPLACE_FRONT(N) \
   BOOST_MOVE_TMPL_LT##N BOOST_MOVE_CLASS##N BOOST_MOVE_GT##N \
   BOOST_CONTAINER_FORCEINLINE void emplace_front(BOOST_MOVE_UREF##N)\
   {\
      if (front_free_capacity())\
      {\
         this->alloc_construct(m_.buffer + m_.front_idx - 1 BOOST_MOVE_I##N BOOST_MOVE_FWD##N);\
         --m_.front_idx;\
      }\
      else\
      {\
         this->emplace_reallocating_slow_path(true, 0 BOOST_MOVE_I##N BOOST_MOVE_FWD##N);\
      }\
      \
      BOOST_ASSERT(invariants_ok());\
   }\
   //
   BOOST_MOVE_ITERATE_0TO9(BOOST_CONTAINER_DEVECTOR_EMPLACE_FRONT)
   #undef BOOST_CONTAINER_DEVECTOR_EMPLACE_FRONT

   #endif

   #if defined(BOOST_CONTAINER_DOXYGEN_INVOKED)
   /**
   * [CopyInsertable]: http://en.cppreference.com/w/cpp/concept/CopyInsertable
   *
   * **Effects**: Pushes the copy of `x` to the front of the devector.
   * Invalidates iterators if reallocation is needed.
   * (`front_free_capacity() == 0`)
   *
   * **Requires**: `T` shall be [CopyInsertable] into `*this`.
   *
   * **Exceptions**: Strong exception guarantee.
   *
   * **Complexity**: Amortized constant in the size of `*this`.
   * (Constant, if `front_free_capacity() > 0`)
   */
   void push_front(const T& x);

   /**
   * [MoveInsertable]: http://en.cppreference.com/w/cpp/concept/MoveInsertable
   *
   * **Effects**: Move constructs a new element at the front of the devector using `x`.
   * Invalidates iterators if reallocation is needed.
   * (`front_free_capacity() == 0`)
   *
   * **Requires**: `T` shall be [MoveInsertable] into `*this`.
   *
   * **Exceptions**: Strong exception guarantee, not regarding the state of `x`.
   *
   * **Complexity**: Amortized constant in the size of `*this`.
   * (Constant, if `front_free_capacity() > 0`)
   */
   void push_front(T&& x);

   #else
   BOOST_MOVE_CONVERSION_AWARE_CATCH(push_front, T, void, priv_push_front)
   #endif

   /**
   * **Effects**: Removes the first element of `*this`.
   *
   * **Precondition**: `!empty()`.
   *
   * **Postcondition**: `front_free_capacity()` is incremented by 1.
   *
   * **Complexity**: Constant.
   */
   void pop_front() BOOST_NOEXCEPT
   {
      BOOST_ASSERT(! empty());
      allocator_traits_type::destroy(get_allocator_ref(), m_.buffer + m_.front_idx);
      ++m_.front_idx;
      BOOST_ASSERT(invariants_ok());
   }

   /**
   * **Effects**: Pushes a new element to the back of the devector.
   * The element is constructed in-place, using the perfect forwarded `args`
   * as constructor arguments. Invalidates iterators if reallocation is needed.
   * (`back_free_capacity() == 0`)
   *
   * **Requires**: `T` shall be [EmplaceConstructible] from `args` and [MoveInsertable] into `*this`,
   * and [MoveAssignable].
   *
   * **Exceptions**: Strong exception guarantee.
   *
   * **Complexity**: Amortized constant in the size of `*this`.
   * (Constant, if `back_free_capacity() > 0`)
   *
   * [EmplaceConstructible]: http://en.cppreference.com/w/cpp/concept/EmplaceConstructible
   * [MoveInsertable]: http://en.cppreference.com/w/cpp/concept/MoveInsertable
   * [MoveAssignable]: http://en.cppreference.com/w/cpp/concept/MoveAssignable
   */
   #if !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES) || defined(BOOST_CONTAINER_DOXYGEN_INVOKED)
   template <class... Args>
   BOOST_CONTAINER_FORCEINLINE void emplace_back(Args&&... args)
   {
      if (this->back_free_capacity()){
         this->alloc_construct(m_.buffer + m_.back_idx, boost::forward<Args>(args)...);
         ++m_.back_idx;
      }
      else {
         this->emplace_reallocating_slow_path(false, size(), boost::forward<Args>(args)...);
      }
      BOOST_ASSERT(invariants_ok());
   }

   #else //!defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES) || defined(BOOST_CONTAINER_DOXYGEN_INVOKED)

   #define BOOST_CONTAINER_DEVECTOR_EMPLACE_BACK(N) \
   BOOST_MOVE_TMPL_LT##N BOOST_MOVE_CLASS##N BOOST_MOVE_GT##N \
   BOOST_CONTAINER_FORCEINLINE void emplace_back(BOOST_MOVE_UREF##N)\
   {\
      if (this->back_free_capacity()){\
         this->alloc_construct(m_.buffer + m_.back_idx BOOST_MOVE_I##N BOOST_MOVE_FWD##N);\
         ++m_.back_idx;\
      }\
      else {\
         this->emplace_reallocating_slow_path(false, size() BOOST_MOVE_I##N BOOST_MOVE_FWD##N);\
      }\
      BOOST_ASSERT(invariants_ok());\
   }\
   //
   BOOST_MOVE_ITERATE_0TO9(BOOST_CONTAINER_DEVECTOR_EMPLACE_BACK)
   #undef BOOST_CONTAINER_DEVECTOR_EMPLACE_BACK

   #endif   //!defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES) || defined(BOOST_CONTAINER_DOXYGEN_INVOKED)


   #if defined(BOOST_CONTAINER_DOXYGEN_INVOKED)
   /**
   * [CopyInsertable]: http://en.cppreference.com/w/cpp/concept/CopyInsertable
   *
   * **Effects**: Pushes the copy of `x` to the back of the devector.
   * Invalidates iterators if reallocation is needed.
   * (`back_free_capacity() == 0`)
   *
   * **Requires**: `T` shall be [CopyInsertable] into `*this`.
   *
   * **Exceptions**: Strong exception guarantee.
   *
   * **Complexity**: Amortized constant in the size of `*this`.
   * (Constant, if `back_free_capacity() > 0`)
   */
   void push_back(const T& x);

   /**
   * [MoveInsertable]: http://en.cppreference.com/w/cpp/concept/MoveInsertable
   *
   * **Effects**: Move constructs a new element at the back of the devector using `x`.
   * Invalidates iterators if reallocation is needed.
   * (`back_free_capacity() == 0`)
   *
   * **Requires**: `T` shall be [MoveInsertable] into `*this`.
   *
   * **Exceptions**: Strong exception guarantee, not regarding the state of `x`.
   *
   * **Complexity**: Amortized constant in the size of `*this`.
   * (Constant, if `back_free_capacity() > 0`)
   */
   void push_back(T&& x);

   #else
   BOOST_MOVE_CONVERSION_AWARE_CATCH(push_back, T, void, priv_push_back)
   #endif

   /**
   * **Effects**: Removes the last element of `*this`.
   *
   * **Precondition**: `!empty()`.
   *
   * **Postcondition**: `back_free_capacity()` is incremented by 1.
   *
   * **Complexity**: Constant.
   */
   void pop_back() BOOST_NOEXCEPT
   {
      BOOST_ASSERT(! empty());
      --m_.back_idx;
      allocator_traits_type::destroy(get_allocator_ref(), m_.buffer + m_.back_idx);
      BOOST_ASSERT(invariants_ok());
   }

   /**
   * **Effects**: Constructs a new element before the element pointed by `position`.
   * The element is constructed in-place, using the perfect forwarded `args`
   * as constructor arguments. Invalidates iterators if reallocation is needed.
   *
   * **Requires**: `T` shall be [EmplaceConstructible], and [MoveInsertable] into `*this`,
   * and [MoveAssignable].
   *
   * **Returns**: Iterator pointing to the newly constructed element.
   *
   * **Exceptions**: Strong exception guarantee if `T` is `NothrowConstructible`
   * and `NothrowAssignable`, Basic exception guarantee otherwise.
   *
   * **Complexity**: Linear in the size of `*this`.
   *
   * [EmplaceConstructible]: http://en.cppreference.com/w/cpp/concept/EmplaceConstructible
   * [MoveInsertable]: http://en.cppreference.com/w/cpp/concept/MoveInsertable
   * [MoveAssignable]: http://en.cppreference.com/w/cpp/concept/MoveAssignable
   */
   #if !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES) || defined(BOOST_CONTAINER_DOXYGEN_INVOKED)
   template <class... Args>
   iterator emplace(const_iterator position, Args&&... args)
   {
      BOOST_ASSERT(position >= begin());
      BOOST_ASSERT(position <= end());

      if (position == end() && back_free_capacity()) // fast path
      {
         this->alloc_construct(m_.buffer + m_.back_idx, boost::forward<Args>(args)...);
         ++m_.back_idx;
         return end() - 1;
      }
      else if (position == begin() && front_free_capacity()) // secondary fast path
      {
         this->alloc_construct(m_.buffer + (m_.front_idx - 1), boost::forward<Args>(args)...);
         --m_.front_idx;
         return begin();
      }
      else
      {
         size_type new_elem_index = position - begin();
         return this->emplace_slow_path(new_elem_index, boost::forward<Args>(args)...);
      }
   }

   #else //!defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES) || defined(BOOST_CONTAINER_DOXYGEN_INVOKED)

   #define BOOST_CONTAINER_DEVECTOR_EMPLACE(N) \
   BOOST_MOVE_TMPL_LT##N BOOST_MOVE_CLASS##N BOOST_MOVE_GT##N \
   iterator emplace(const_iterator position BOOST_MOVE_I##N BOOST_MOVE_UREF##N)\
   {\
      BOOST_ASSERT(position >= begin());\
      BOOST_ASSERT(position <= end());\
      \
      if (position == end() && back_free_capacity()){\
         this->alloc_construct(m_.buffer + m_.back_idx BOOST_MOVE_I##N BOOST_MOVE_FWD##N);\
         ++m_.back_idx;\
         return end() - 1;\
      }\
      else if (position == begin() && front_free_capacity()){\
         this->alloc_construct(m_.buffer + m_.front_idx - 1 BOOST_MOVE_I##N BOOST_MOVE_FWD##N);\
         --m_.front_idx;\
         return begin();\
      }\
      else{\
         size_type new_elem_index = position - begin();\
         return this->emplace_slow_path(new_elem_index BOOST_MOVE_I##N BOOST_MOVE_FWD##N);\
      }\
   }\
   //
   BOOST_MOVE_ITERATE_0TO9(BOOST_CONTAINER_DEVECTOR_EMPLACE)
   #undef BOOST_CONTAINER_DEVECTOR_EMPLACE

   #endif   //!defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES) || defined(BOOST_CONTAINER_DOXYGEN_INVOKED)


   #if defined(BOOST_CONTAINER_DOXYGEN_INVOKED)
   /**
   * **Effects**: Copy constructs a new element before the element pointed by `position`,
   * using `x` as constructor argument. Invalidates iterators if reallocation is needed.
   *
   * **Requires**: `T` shall be [CopyInsertable] into `*this` and and [CopyAssignable].
   *
   * **Returns**: Iterator pointing to the newly constructed element.
   *
   * **Exceptions**: Strong exception guarantee if `T` is `NothrowConstructible`
   * and `NothrowAssignable`, Basic exception guarantee otherwise.
   *
   * **Complexity**: Linear in the size of `*this`.
   *
   * [CopyInsertable]: http://en.cppreference.com/w/cpp/concept/CopyInsertable
   * [CopyAssignable]: http://en.cppreference.com/w/cpp/concept/CopyAssignable
   */
   iterator insert(const_iterator position, const T &x);

   /**
   * **Effects**: Move constructs a new element before the element pointed by `position`,
   * using `x` as constructor argument. Invalidates iterators if reallocation is needed.
   *
   * **Requires**: `T` shall be [MoveInsertable] into `*this` and and [CopyAssignable].
   *
   * **Returns**: Iterator pointing to the newly constructed element.
   *
   * **Exceptions**: Strong exception guarantee if `T` is `NothrowConstructible`
   * and `NothrowAssignable` (not regarding the state of `x`),
   * Basic exception guarantee otherwise.
   *
   * **Complexity**: Linear in the size of `*this`.
   *
   * [MoveInsertable]: http://en.cppreference.com/w/cpp/concept/MoveInsertable
   * [CopyAssignable]: http://en.cppreference.com/w/cpp/concept/CopyAssignable
   */
   iterator insert(const_iterator position, T &&x);
   #else
   BOOST_MOVE_CONVERSION_AWARE_CATCH_1ARG(insert, T, iterator, priv_insert, const_iterator, const_iterator)
   #endif

   /**
   * **Effects**: Copy constructs `n` elements before the element pointed by `position`,
   * using `x` as constructor argument. Invalidates iterators if reallocation is needed.
   *
   * **Requires**: `T` shall be [CopyInsertable] into `*this` and and [CopyAssignable].
   *
   * **Returns**: Iterator pointing to the first inserted element, or `position`, if `n` is zero.
   *
   * **Exceptions**: Strong exception guarantee if `T` is `NothrowConstructible`
   * and `NothrowAssignable`, Basic exception guarantee otherwise.
   *
   * **Complexity**: Linear in the size of `*this` and `n`.
   *
   * [CopyInsertable]: http://en.cppreference.com/w/cpp/concept/CopyInsertable
   * [CopyAssignable]: http://en.cppreference.com/w/cpp/concept/CopyAssignable
   */
   iterator insert(const_iterator position, size_type n, const T& x)
   {
      cvalue_iterator first(x, n);
      cvalue_iterator last = first + n;
      return insert_range(position, first, last);
   }

   /**
   * **Effects**: Copy constructs elements before the element pointed by position
   * using each element in the rage pointed by `first` and `last` as constructor arguments.
   * Invalidates iterators if reallocation is needed.
   *
   * **Requires**: `T` shall be [EmplaceConstructible] into `*this` from `*first`. If the specified iterator
   * does not meet the forward iterator requirements, `T` shall also be [MoveInsertable] into `*this`
   * and [MoveAssignable].
   *
   * **Precondition**: `first` and `last` are not iterators into `*this`.
   *
   * **Returns**: Iterator pointing to the first inserted element, or `position`, if `first == last`.
   *
   * **Complexity**: Linear in the size of `*this` and `N` (where `N` is the distance between `first` and `last`).
   * Makes only `N` calls to the constructor of `T` and no reallocations if iterators `first` and `last`
   * are of forward, bidirectional, or random access categories. It makes 2N calls to the copy constructor of `T`
   * and allocates memory twice at most if they are just input iterators.
   *
   * **Exceptions**: Strong exception guarantee if `T` is `NothrowConstructible`
   * and `NothrowAssignable`, Basic exception guarantee otherwise.
   *
   * **Remarks**: Each iterator in the range `[first,last)` shall be dereferenced exactly once,
   * unless an exception is thrown.
   *
   * [EmplaceConstructible]: http://en.cppreference.com/w/cpp/concept/EmplaceConstructible
   * [MoveInsertable]: http://en.cppreference.com/w/cpp/concept/MoveInsertable
   * [MoveAssignable]: http://en.cppreference.com/w/cpp/concept/MoveAssignable
   */
   template <class InputIterator>
   iterator insert(const_iterator position, InputIterator first, InputIterator last
      //Input iterators
      BOOST_CONTAINER_DOCIGN(BOOST_MOVE_I typename dtl::disable_if_or
         < void
         BOOST_MOVE_I dtl::is_convertible<InputIterator BOOST_MOVE_I size_type>
         BOOST_MOVE_I dtl::is_not_input_iterator<InputIterator>
         >::type * = 0)
      )
   {
      if (position == end())
      {
         size_type insert_index = size();

         for (; first != last; ++first)
         {
            this->emplace_back(*first);
         }

         return begin() + insert_index;
      }
      else
      {
         const size_type insert_index = static_cast<size_type>(position - this->cbegin());
         const size_type old_size = static_cast<size_type>(this->size());

         for (; first != last; ++first) {
            this->emplace_back(*first);
         }
         iterator rit (this->begin() + insert_index);
         boost::movelib::rotate_gcd(rit, this->begin() + old_size, this->begin() + this->size());
         return rit;
      }
   }

   #ifndef BOOST_CONTAINER_DOXYGEN_INVOKED

   template <class ForwardIterator>
   iterator insert(const_iterator position, ForwardIterator first, ForwardIterator last
      //Other iterators
      BOOST_CONTAINER_DOCIGN(BOOST_MOVE_I typename dtl::disable_if_or
         < void
         BOOST_MOVE_I dtl::is_convertible<ForwardIterator BOOST_MOVE_I size_type>
         BOOST_MOVE_I dtl::is_input_iterator<ForwardIterator>
         >::type * = 0)
      )
   {
      return insert_range(position, first, last);
   }

   #endif // ifndef BOOST_CONTAINER_DOXYGEN_INVOKED

   #if !defined(BOOST_NO_CXX11_HDR_INITIALIZER_LIST)
   /** **Equivalent to**: `insert(position, il.begin(), il.end())` */
   iterator insert(const_iterator position, std::initializer_list<T> il)
   {
      return insert_range(position, il.begin(), il.end());
   }
   #endif

   /**
   * [MoveAssignable]: http://en.cppreference.com/w/cpp/concept/MoveAssignable
   *
   * **Effects**: Destroys the element pointed by `position` and removes it from the devector.
   * Invalidates iterators.
   *
   * **Requires**: `T` shall be [MoveAssignable].
   *
   * **Precondition**: `position` must be in the range of `[begin(), end())`.
   *
   * **Returns**: Iterator pointing to the element immediately following the erased element
   * prior to its erasure. If no such element exists, `end()` is returned.
   *
   * **Exceptions**: Strong exception guarantee if `T` is `NothrowAssignable`,
   * Basic exception guarantee otherwise.
   *
   * **Complexity**: Linear in half the size of `*this`.
   */
   iterator erase(const_iterator position)
   {
      return erase(position, position + 1);
   }

   /**
   * [MoveAssignable]: http://en.cppreference.com/w/cpp/concept/MoveAssignable
   *
   * **Effects**: Destroys the range `[first,last)` and removes it from the devector.
   * Invalidates iterators.
   *
   * **Requires**: `T` shall be [MoveAssignable].
   *
   * **Precondition**: `[first,last)` must be in the range of `[begin(), end())`.
   *
   * **Returns**: Iterator pointing to the element pointed to by `last` prior to any elements
   * being erased. If no such element exists, `end()` is returned.
   *
   * **Exceptions**: Strong exception guarantee if `T` is `NothrowAssignable`,
   * Basic exception guarantee otherwise.
   *
   * **Complexity**: Linear in half the size of `*this`
   * plus the distance between `first` and `last`.
   */
   iterator erase(const_iterator first, const_iterator last)
   {
      iterator nc_first = begin() + (first - begin());
      iterator nc_last  = begin() + (last  - begin());
      return erase(nc_first, nc_last);
   }

   /**
   * [MoveAssignable]: http://en.cppreference.com/w/cpp/concept/MoveAssignable
   *
   * **Effects**: Destroys the range `[first,last)` and removes it from the devector.
   * Invalidates iterators.
   *
   * **Requires**: `T` shall be [MoveAssignable].
   *
   * **Precondition**: `[first,last)` must be in the range of `[begin(), end())`.
   *
   * **Returns**: Iterator pointing to the element pointed to by `last` prior to any elements
   * being erased. If no such element exists, `end()` is returned.
   *
   * **Exceptions**: Strong exception guarantee if `T` is `NothrowAssignable`,
   * Basic exception guarantee otherwise.
   *
   * **Complexity**: Linear in half the size of `*this`.
   */
   iterator erase(iterator first, iterator last)
   {
      size_type front_distance = last - begin();
      size_type back_distance = end() - first;
      size_type n = boost::container::iterator_distance(first, last);

      if (front_distance < back_distance)
      {
         // move n to the right
         boost::container::move_backward(begin(), first, last);

         for (iterator i = begin(); i != begin() + n; ++i)
         {
            allocator_traits_type::destroy(get_allocator_ref(), i);
         }
         //n is always less than max stored_size_type
         m_.set_front_idx(m_.front_idx + n);

         BOOST_ASSERT(invariants_ok());
         return last;
      }
      else {
         // move n to the left
         boost::container::move(last, end(), first);

         for (iterator i = end() - n; i != end(); ++i)
         {
            allocator_traits_type::destroy(get_allocator_ref(), i);
         }
         //n is always less than max stored_size_type
         m_.set_back_idx(m_.back_idx - n);

         BOOST_ASSERT(invariants_ok());
         return first;
      }
   }

   /**
   * [MoveInsertable]: http://en.cppreference.com/w/cpp/concept/MoveInsertable
   *
   * **Effects**: exchanges the contents of `*this` and `b`.
   *
   * **Requires**: instances of `T` must be swappable by unqualified call of `swap`
   * and `T` must be [MoveInsertable] into `*this`.
   *
   * **Precondition**: The allocators should allow propagation or should compare equal.
   *
   * **Exceptions**: Basic exceptions guarantee if not `noexcept`.
   *
   * **Complexity**: Constant.
   */
   void swap(devector& b)
      BOOST_NOEXCEPT_IF( allocator_traits_type::propagate_on_container_swap::value
                        || allocator_traits_type::is_always_equal::value)
   {
      BOOST_CONSTEXPR_OR_CONST bool propagate_alloc = allocator_traits_type::propagate_on_container_swap::value;
      BOOST_ASSERT(propagate_alloc || get_allocator_ref() == b.get_allocator_ref()); // else it's undefined behavior

      swap_big_big(*this, b);

      // swap indices
      boost::adl_move_swap(m_.front_idx, b.m_.front_idx);
      boost::adl_move_swap(m_.back_idx, b.m_.back_idx);

      //And now swap the allocator
      dtl::swap_alloc(this->get_allocator_ref(), b.get_allocator_ref(), dtl::bool_<propagate_alloc>());

      BOOST_ASSERT(  invariants_ok());
      BOOST_ASSERT(b.invariants_ok());
   }

   /**
   * **Effects**: Destroys all elements in the devector.
   * Invalidates all references, pointers and iterators to the
   * elements of the devector.
   *
   * **Postcondition**: `empty() && front_free_capacity() == 0
   * && back_free_capacity() == old capacity`.
   *
   * **Complexity**: Linear in the size of `*this`.
   *
   * **Remarks**: Does not free memory.
   */
   void clear() BOOST_NOEXCEPT
   {
      destroy_elements(begin(), end());
      m_.front_idx = m_.back_idx = 0;
   }

   BOOST_CONTAINER_FORCEINLINE friend bool operator==(const devector& x, const devector& y)
   {  return x.size() == y.size() && ::boost::container::algo_equal(x.begin(), x.end(), y.begin());  }

   BOOST_CONTAINER_FORCEINLINE friend bool operator!=(const devector& x, const devector& y)
   {  return !(x == y); }

   friend bool operator< (const devector& x, const devector& y)
   {  return boost::container::algo_lexicographical_compare(x.begin(), x.end(), y.begin(), y.end());  }

   BOOST_CONTAINER_FORCEINLINE friend bool operator>(const devector& x, const devector& y)
   {  return y < x;  }

   BOOST_CONTAINER_FORCEINLINE friend bool operator<=(const devector& x, const devector& y)
   {  return !(y < x);  }

   BOOST_CONTAINER_FORCEINLINE friend bool operator>=(const devector& x, const devector& y)
   {  return !(x < y);  }

   BOOST_CONTAINER_FORCEINLINE friend void swap(devector& x, devector& y)
   {  x.swap(y);  }

   private:
   #ifndef BOOST_CONTAINER_DOXYGEN_INVOKED

   T* raw_begin() BOOST_NOEXCEPT
   {  return boost::movelib::to_raw_pointer(m_.buffer) + m_.front_idx;  }

   T* raw_end() BOOST_NOEXCEPT
   {  return boost::movelib::to_raw_pointer(m_.buffer) + m_.back_idx;   }


   template <class U>
   BOOST_CONTAINER_FORCEINLINE void priv_push_front(BOOST_FWD_REF(U) u)
   {
      this->emplace_front(boost::forward<U>(u));
   }

   template <class U>
   BOOST_CONTAINER_FORCEINLINE void priv_push_back(BOOST_FWD_REF(U) u)
   {
      this->emplace_back(boost::forward<U>(u));
   }

   template <class U>
   BOOST_CONTAINER_FORCEINLINE iterator priv_insert(const_iterator pos, BOOST_FWD_REF(U) u)
   {
      return this->emplace(pos, boost::forward<U>(u));
   }

   // allocator_type wrappers

   BOOST_CONTAINER_FORCEINLINE allocator_type& get_allocator_ref() BOOST_NOEXCEPT
   {
      return static_cast<allocator_type&>(m_);
   }

   BOOST_CONTAINER_FORCEINLINE const allocator_type& get_allocator_ref() const BOOST_NOEXCEPT
   {
      return static_cast<const allocator_type&>(m_);
   }

   pointer allocate(size_type capacity)
   {
      //First detect overflow on smaller stored_size_types
      if (capacity > stored_size_type(-1)){
         boost::container::throw_length_error("get_next_capacity, allocator's max size reached");
      }
      //(clamp_by_stored_size_type<size_type>)(prefer_in_recvd_out_size, stored_size_type());
      #ifdef BOOST_CONTAINER_DEVECTOR_ALLOC_STATS
      ++m_.capacity_alloc_count;
      #endif // BOOST_CONTAINER_DEVECTOR_ALLOC_STATS
      return allocator_traits_type::allocate(get_allocator_ref(), capacity);
   }

   void destroy_elements(pointer begin, pointer end)
   {
      for (; begin != end; ++begin)
      {
         allocator_traits_type::destroy(get_allocator_ref(), begin);
      }
   }

   void deallocate_buffer()
   {
      if (m_.buffer)
      {
      allocator_traits_type::deallocate(get_allocator_ref(), m_.buffer, m_.capacity);
      }
   }

   #if !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES) || defined(BOOST_CONTAINER_DOXYGEN_INVOKED)
   template <typename... Args>
   BOOST_CONTAINER_FORCEINLINE void alloc_construct(pointer dst, Args&&... args)
   {
      allocator_traits_type::construct(
         get_allocator_ref(),
         dst,
         boost::forward<Args>(args)...
      );
   }

   template <typename... Args>
   void construct_n(pointer buffer, size_type n, Args&&... args)
   {
      detail::construction_guard<allocator_type> ctr_guard(buffer, get_allocator_ref());
      guarded_construct_n(buffer, n, ctr_guard, boost::forward<Args>(args)...);
      ctr_guard.release();
   }

   template <typename... Args>
   void guarded_construct_n(pointer buffer, size_type n, detail::construction_guard<allocator_type>& ctr_guard, Args&&... args)
   {
      for (size_type i = 0; i < n; ++i) {
         this->alloc_construct(buffer + i, boost::forward<Args>(args)...);
         ctr_guard.extend();
      }
   }

   #else //!defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES) || defined(BOOST_CONTAINER_DOXYGEN_INVOKED)

   #define BOOST_CONTAINER_DEVECTOR_ALLOC_CONSTRUCT(N) \
   BOOST_MOVE_TMPL_LT##N BOOST_MOVE_CLASS##N BOOST_MOVE_GT##N \
   BOOST_CONTAINER_FORCEINLINE void alloc_construct(pointer dst BOOST_MOVE_I##N BOOST_MOVE_UREF##N)\
   {\
      allocator_traits_type::construct(\
         get_allocator_ref(), dst BOOST_MOVE_I##N BOOST_MOVE_FWD##N );\
   }\
   \
   BOOST_MOVE_TMPL_LT##N BOOST_MOVE_CLASS##N BOOST_MOVE_GT##N \
   void construct_n(pointer buffer, size_type n BOOST_MOVE_I##N BOOST_MOVE_UREF##N)\
   {\
      detail::construction_guard<allocator_type> ctr_guard(buffer, get_allocator_ref());\
      guarded_construct_n(buffer, n, ctr_guard BOOST_MOVE_I##N BOOST_MOVE_FWD##N);\
      ctr_guard.release();\
   }\
   \
   BOOST_MOVE_TMPL_LT##N BOOST_MOVE_CLASS##N BOOST_MOVE_GT##N \
   void guarded_construct_n(pointer buffer, size_type n, detail::construction_guard<allocator_type>& ctr_guard BOOST_MOVE_I##N BOOST_MOVE_UREF##N)\
   {\
      for (size_type i = 0; i < n; ++i) {\
         this->alloc_construct(buffer + i BOOST_MOVE_I##N BOOST_MOVE_FWD##N);\
         ctr_guard.extend();\
      }\
   }
   //
   BOOST_MOVE_ITERATE_0TO9(BOOST_CONTAINER_DEVECTOR_ALLOC_CONSTRUCT)
   #undef BOOST_CONTAINER_DEVECTOR_ALLOC_CONSTRUCT

   #endif   //!defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES) || defined(BOOST_CONTAINER_DOXYGEN_INVOKED)

   size_type front_capacity() const
   {
      return m_.back_idx;
   }

   size_type back_capacity() const
   {
      return m_.capacity - m_.front_idx;
   }

   size_type calculate_new_capacity(size_type requested_capacity)
   {
      size_type max = allocator_traits_type::max_size(this->get_allocator_ref());
      (clamp_by_stored_size_type)(max, stored_size_type());
      const size_type remaining_additional_cap = max - size_type(m_.capacity);
      const size_type min_additional_cap = requested_capacity - size_type(m_.capacity);
      if ( remaining_additional_cap < min_additional_cap )
         boost::container::throw_length_error("devector: get_next_capacity, max size exceeded");

      return growth_factor_type()( size_type(m_.capacity), min_additional_cap, max);
   }

   void buffer_move_or_copy(pointer dst)
   {
      detail::construction_guard<allocator_type> guard(dst, get_allocator_ref());

      buffer_move_or_copy(dst, guard);

      guard.release();
   }

   void buffer_move_or_copy(pointer dst, detail::construction_guard<allocator_type>& guard)
   {
      opt_move_or_copy(begin(), end(), dst, guard);

      destroy_elements(data(), data() + size());
      deallocate_buffer();
   }

   void opt_move_or_copy(pointer begin, pointer end, pointer dst)
   {
      typedef typename dtl::if_c
         < boost::move_detail::is_nothrow_copy_constructible<T>::value || boost::is_nothrow_move_constructible<T>::value
         , detail::null_construction_guard
         , detail::construction_guard<allocator_type>
         >::type guard_t;

      guard_t guard(dst, get_allocator_ref());

      opt_move_or_copy(begin, end, dst, guard);

      guard.release();
   }

   template <typename Guard>
   void opt_move_or_copy(pointer begin, pointer end, pointer dst, Guard& guard)
   {
      // if trivial copy and default allocator, memcpy
      boost::container::uninitialized_move_alloc(get_allocator_ref(), begin, end, dst);
      guard.extend();
   }

   template <typename Iterator>
   void opt_copy(Iterator begin, Iterator end, pointer dst)
   {
      typedef typename dtl::if_c
         < boost::move_detail::is_nothrow_copy_constructible<T>::value
         , detail::null_construction_guard
         , detail::construction_guard<allocator_type>
         >::type guard_t;

      guard_t guard(dst, get_allocator_ref());

      opt_copy(begin, end, dst, guard);

      guard.release();
   }

   template <typename Iterator, typename Guard>
   void opt_copy(Iterator begin, Iterator end, pointer dst, Guard& guard)
   {
      while (begin != end)
      {
         this->alloc_construct(dst++, *begin++);
         guard.extend();
      }
   }

   template <typename Guard>
   void opt_copy(const_pointer begin, const_pointer end, pointer dst, Guard& guard)
   {
      // if trivial copy and default allocator, memcpy
      boost::container::uninitialized_copy_alloc(get_allocator_ref(), begin, end, dst);
      guard.extend();
   }

   #if !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES) || defined(BOOST_CONTAINER_DOXYGEN_INVOKED)

   template <typename... Args>
   void resize_front_impl(size_type sz , Args&&... args)
   {
      if (sz > size())
      {
         const size_type n = sz - size();

         if (sz <= front_capacity())
         {
            construct_n(m_.buffer + m_.front_idx - n, n, boost::forward<Args>(args)...);
            m_.set_front_idx(m_.front_idx - n);
         }
         else
         {
            resize_front_slow_path(sz, n, boost::forward<Args>(args)...);
         }
      }
      else {
         while (this->size() > sz)
         {
            this->pop_front();
         }
      }
   }

   template <typename... Args>
   void resize_front_slow_path(size_type sz, size_type n, Args&&... args)
   {
      const size_type new_capacity = calculate_new_capacity(sz + back_free_capacity());
      pointer new_buffer = allocate(new_capacity);
      allocation_guard new_buffer_guard(new_buffer, new_capacity, get_allocator_ref());

      const size_type new_old_elem_index = new_capacity - size();
      const size_type new_elem_index = new_old_elem_index - n;

      detail::construction_guard<allocator_type> guard(new_buffer + new_elem_index, get_allocator_ref());
      guarded_construct_n(new_buffer + new_elem_index, n, guard, boost::forward<Args>(args)...);

      buffer_move_or_copy(new_buffer + new_old_elem_index, guard);

      guard.release();
      new_buffer_guard.release();

      m_.buffer = new_buffer;
      m_.set_capacity(new_capacity);
      m_.set_back_idx(new_old_elem_index + m_.back_idx - m_.front_idx);
      m_.set_front_idx(new_elem_index);
   }

   template <typename... Args>
   void resize_back_impl(size_type sz, Args&&... args)
   {
      if (sz > size())
      {
         const size_type n = sz - size();

         if (sz <= back_capacity())
         {
            construct_n(m_.buffer + m_.back_idx, n, boost::forward<Args>(args)...);
            m_.set_back_idx(m_.back_idx + n);
         }
         else
         {
            resize_back_slow_path(sz, n, boost::forward<Args>(args)...);
         }
      }
      else
      {
         while (size() > sz)
         {
            pop_back();
         }
      }
   }

   template <typename... Args>
   void resize_back_slow_path(size_type sz, size_type n, Args&&... args)
   {
      const size_type new_capacity = calculate_new_capacity(sz + front_free_capacity());
      pointer new_buffer = allocate(new_capacity);
      allocation_guard new_buffer_guard(new_buffer, new_capacity, get_allocator_ref());

      detail::construction_guard<allocator_type> guard(new_buffer + m_.back_idx, get_allocator_ref());
      guarded_construct_n(new_buffer + m_.back_idx, n, guard, boost::forward<Args>(args)...);

      buffer_move_or_copy(new_buffer + m_.front_idx);

      guard.release();
      new_buffer_guard.release();

      m_.buffer = new_buffer;
      m_.set_capacity(new_capacity);
      m_.set_back_idx(m_.back_idx + n);
   }

   template <typename... Args>
   iterator emplace_slow_path(size_type new_elem_index, Args&&... args)
   {
      pointer position = begin() + new_elem_index;

      // prefer moving front to access memory forward if there are less elems to move
      bool prefer_move_front = new_elem_index <= size()/2;

      if (front_free_capacity() && (!back_free_capacity() || prefer_move_front))
      {
         BOOST_ASSERT(size() >= 1);

         // move things closer to the front a bit

         // avoid invalidating any reference in args later
         T tmp(boost::forward<Args>(args)...);

         // construct at front - 1 from front (no guard)
         this->alloc_construct(begin() - 1, boost::move(*begin()));

         // move front half left
         boost::move(begin() + 1, position, begin());
         --m_.front_idx;

         // move assign new elem before pos
         --position;
         *position = boost::move(tmp);

         return position;
      }
      else if (back_free_capacity()) {
         BOOST_ASSERT(size() >= 1);

         // move things closer to the end a bit

         // avoid invalidating any reference in args later
         T tmp(boost::forward<Args>(args)...);

         // construct at back + 1 from back (no guard)
         this->alloc_construct(end(), boost::move(back()));

         // move back half right
         boost::container::move_backward(position, end() - 1, end());
         ++m_.back_idx;

         // move assign new elem to pos
         *position = boost::move(tmp);

         return position;
      }
      else
      {
         return emplace_reallocating_slow_path(prefer_move_front, new_elem_index, boost::forward<Args>(args)...);
      }
   }

   template <typename... Args>
   pointer emplace_reallocating_slow_path(bool make_front_free, size_type new_elem_index, Args&&... args)
   {
      // reallocate
      size_type new_capacity = calculate_new_capacity(capacity() + 1);
      pointer new_buffer = allocate(new_capacity);

      // guard allocation
      allocation_guard new_buffer_guard(new_buffer, new_capacity, get_allocator_ref());

      size_type new_front_index = (make_front_free)
         ? new_capacity - back_free_capacity() - size() - 1
         : m_.front_idx;

      iterator new_begin = new_buffer + new_front_index;
      iterator new_position = new_begin + new_elem_index;
      iterator old_position = begin() + new_elem_index;

      // construct new element (and guard it)
      this->alloc_construct(new_position, boost::forward<Args>(args)...);

      detail::construction_guard<allocator_type> second_half_guard(new_position, get_allocator_ref());
      second_half_guard.extend();

      // move front-pos (possibly guarded)
      detail::construction_guard<allocator_type> first_half_guard(new_begin, get_allocator_ref());
      opt_move_or_copy(begin(), old_position, new_begin, first_half_guard);

      // move pos+1-end (possibly guarded)
      opt_move_or_copy(old_position, end(), new_position + 1, second_half_guard);

      // cleanup
      destroy_elements(begin(), end());
      deallocate_buffer();

      // release alloc and other guards
      second_half_guard.release();
      first_half_guard.release();
      new_buffer_guard.release();

      // rebind members
      m_.set_capacity(new_capacity);
      m_.buffer = new_buffer;
      m_.set_back_idx(new_front_index + size() + 1);
      m_.set_front_idx(new_front_index);

      return new_position;
   }

   #else //!defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES) || defined(BOOST_CONTAINER_DOXYGEN_INVOKED)

   #define BOOST_CONTAINER_DEVECTOR_SLOW_PATH(N) \
   BOOST_MOVE_TMPL_LT##N BOOST_MOVE_CLASS##N BOOST_MOVE_GT##N \
   void resize_front_impl(size_type sz BOOST_MOVE_I##N BOOST_MOVE_UREF##N)\
   {\
      if (sz > size())\
      {\
         const size_type n = sz - size();\
         if (sz <= front_capacity()){\
            construct_n(m_.buffer + m_.front_idx - n, n BOOST_MOVE_I##N BOOST_MOVE_FWD##N);\
            m_.set_front_idx(m_.front_idx - n);\
         }\
         else\
         {\
            resize_front_slow_path(sz, n BOOST_MOVE_I##N BOOST_MOVE_FWD##N);\
         }\
      }\
      else {\
         while (this->size() > sz)\
         {\
            this->pop_front();\
         }\
      }\
   }\
   \
   BOOST_MOVE_TMPL_LT##N BOOST_MOVE_CLASS##N BOOST_MOVE_GT##N \
   void resize_front_slow_path(size_type sz, size_type n BOOST_MOVE_I##N BOOST_MOVE_UREF##N)\
   {\
      const size_type new_capacity = calculate_new_capacity(sz + back_free_capacity());\
      pointer new_buffer = allocate(new_capacity);\
      allocation_guard new_buffer_guard(new_buffer, new_capacity, get_allocator_ref());\
   \
      const size_type new_old_elem_index = new_capacity - size();\
      const size_type new_elem_index = new_old_elem_index - n;\
   \
      detail::construction_guard<allocator_type> guard(new_buffer + new_elem_index, get_allocator_ref());\
      guarded_construct_n(new_buffer + new_elem_index, n, guard BOOST_MOVE_I##N BOOST_MOVE_FWD##N);\
   \
      buffer_move_or_copy(new_buffer + new_old_elem_index, guard);\
   \
      guard.release();\
      new_buffer_guard.release();\
      m_.buffer = new_buffer;\
      m_.set_capacity(new_capacity);\
      m_.set_back_idx(new_old_elem_index + m_.back_idx - m_.front_idx);\
      m_.set_front_idx(new_elem_index);\
   }\
   \
   BOOST_MOVE_TMPL_LT##N BOOST_MOVE_CLASS##N BOOST_MOVE_GT##N \
   void resize_back_impl(size_type sz BOOST_MOVE_I##N BOOST_MOVE_UREF##N)\
   {\
      if (sz > size())\
      {\
         const size_type n = sz - size();\
      \
         if (sz <= back_capacity())\
         {\
            construct_n(m_.buffer + m_.back_idx, n BOOST_MOVE_I##N BOOST_MOVE_FWD##N);\
            m_.set_back_idx(m_.back_idx + n);\
         }\
         else\
         {\
            resize_back_slow_path(sz, n BOOST_MOVE_I##N BOOST_MOVE_FWD##N);\
         }\
      }\
      else\
      {\
         while (size() > sz)\
         {\
            pop_back();\
         }\
      }\
   }\
   \
   BOOST_MOVE_TMPL_LT##N BOOST_MOVE_CLASS##N BOOST_MOVE_GT##N \
   void resize_back_slow_path(size_type sz, size_type n BOOST_MOVE_I##N BOOST_MOVE_UREF##N)\
   {\
      const size_type new_capacity = calculate_new_capacity(sz + front_free_capacity());\
      pointer new_buffer = allocate(new_capacity);\
      allocation_guard new_buffer_guard(new_buffer, new_capacity, get_allocator_ref());\
   \
      detail::construction_guard<allocator_type> guard(new_buffer + m_.back_idx, get_allocator_ref());\
      guarded_construct_n(new_buffer + m_.back_idx, n, guard BOOST_MOVE_I##N BOOST_MOVE_FWD##N);\
   \
      buffer_move_or_copy(new_buffer + m_.front_idx);\
   \
      guard.release();\
      new_buffer_guard.release();\
   \
      m_.buffer = new_buffer;\
      m_.set_capacity(new_capacity);\
      m_.set_back_idx(m_.back_idx + n);\
   }\
   \
   BOOST_MOVE_TMPL_LT##N BOOST_MOVE_CLASS##N BOOST_MOVE_GT##N \
   iterator emplace_slow_path(size_type new_elem_index BOOST_MOVE_I##N BOOST_MOVE_UREF##N)\
   {\
      pointer position = begin() + new_elem_index;\
   \
      bool prefer_move_front = new_elem_index <= size()/2;\
   \
      if (front_free_capacity() && (!back_free_capacity() || prefer_move_front))\
      {\
         BOOST_ASSERT(size() >= 1);\
         typename dtl::aligned_storage<sizeof(T), dtl::alignment_of<T>::value>::type v;\
         T *vp = reinterpret_cast<T *>(v.data);\
         allocator_traits_type::construct(get_stored_allocator(), vp BOOST_MOVE_I##N BOOST_MOVE_FWD##N);\
         T &tmp = *vp;\
         dtl::value_destructor<allocator_type> on_exit(get_stored_allocator(), tmp); (void)on_exit;\
         \
         this->alloc_construct(begin() - 1, boost::move(*begin()));\
         boost::move(begin() + 1, position, begin());\
         --m_.front_idx;\
         --position;\
         *position = boost::move(tmp);\
         return position;\
      }\
      else if (back_free_capacity()) {\
         BOOST_ASSERT(size() >= 1);\
         typename dtl::aligned_storage<sizeof(T), dtl::alignment_of<T>::value>::type v;\
         T *vp = reinterpret_cast<T *>(v.data);\
         allocator_traits_type::construct(get_stored_allocator(), vp BOOST_MOVE_I##N BOOST_MOVE_FWD##N);\
         T &tmp = *vp;\
         dtl::value_destructor<allocator_type> on_exit(get_stored_allocator(), tmp); (void)on_exit;\
         this->alloc_construct(end(), boost::move(back()));\
         boost::container::move_backward(position, end() - 1, end());\
         ++m_.back_idx;\
         *position = boost::move(tmp);\
         return position;\
      }\
      else {\
         return emplace_reallocating_slow_path(prefer_move_front, new_elem_index BOOST_MOVE_I##N BOOST_MOVE_FWD##N);\
      }\
   }\
   \
   BOOST_MOVE_TMPL_LT##N BOOST_MOVE_CLASS##N BOOST_MOVE_GT##N \
   pointer emplace_reallocating_slow_path(bool make_front_free, size_type new_elem_index BOOST_MOVE_I##N BOOST_MOVE_UREF##N)\
   {\
      size_type new_capacity = calculate_new_capacity(capacity() + 1);\
      pointer new_buffer = allocate(new_capacity);\
      allocation_guard new_buffer_guard(new_buffer, new_capacity, get_allocator_ref());\
      size_type new_front_index = (make_front_free)\
         ? new_capacity - back_free_capacity() - size() - 1\
         : m_.front_idx;\
      iterator new_begin = new_buffer + new_front_index;\
      iterator new_position = new_begin + new_elem_index;\
      iterator old_position = begin() + new_elem_index;\
      this->alloc_construct(new_position BOOST_MOVE_I##N BOOST_MOVE_FWD##N);\
      detail::construction_guard<allocator_type> second_half_guard(new_position, get_allocator_ref());\
      second_half_guard.extend();\
      detail::construction_guard<allocator_type> first_half_guard(new_begin, get_allocator_ref());\
      opt_move_or_copy(begin(), old_position, new_begin, first_half_guard);\
      opt_move_or_copy(old_position, end(), new_position + 1, second_half_guard);\
      destroy_elements(begin(), end());\
      deallocate_buffer();\
      second_half_guard.release();\
      first_half_guard.release();\
      new_buffer_guard.release();\
      m_.set_capacity(new_capacity);\
      m_.buffer = new_buffer;\
      m_.set_back_idx(new_front_index + size() + 1);\
      m_.set_front_idx(new_front_index);\
      return new_position;\
   }\
   //
   BOOST_MOVE_ITERATE_0TO9(BOOST_CONTAINER_DEVECTOR_SLOW_PATH)
   #undef BOOST_CONTAINER_DEVECTOR_SLOW_PATH

   #endif   //!defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES) || defined(BOOST_CONTAINER_DOXYGEN_INVOKED)
/*
   void unsafe_uninitialized_grow_front(size_type n)
   {
      BOOST_ASSERT(n >= size());

      size_type need = n - size();

      if (need > front_free_capacity())
      {
         reallocate_at(n + back_free_capacity(), need);
      }

      m_.set_front_idx(m_.front_idx - need);
   }

   void unsafe_uninitialized_shrink_front(size_type n)
   {
      BOOST_ASSERT(n <= size());

      size_type doesnt_need = size() - n;
      m_.set_front_idx(m_.front_idx + doesnt_need);
   }

   void unsafe_uninitialized_grow_back(size_type n)
   {
      BOOST_ASSERT(n >= size());

      size_type need = n - size();

      if (need > back_free_capacity())
      {
         reallocate_at(n + front_free_capacity(), front_free_capacity());
      }

      m_.set_back_idx(m_.back_idx + need);
   }

   void unsafe_uninitialized_shrink_back(size_type n)
   {
      BOOST_ASSERT(n <= size());

      size_type doesnt_need = size() - n;
      m_.set_back_idx(m_.back_idx - doesnt_need);
   }
*/

   void reallocate_at(size_type new_capacity, size_type buffer_offset)
   {
      pointer new_buffer = allocate(new_capacity);
      allocation_guard new_buffer_guard(new_buffer, new_capacity, get_allocator_ref());

      buffer_move_or_copy(new_buffer + buffer_offset);

      new_buffer_guard.release();

      m_.buffer = new_buffer;
      //Safe cast, allocate() will handle stored_size_type overflow
      m_.set_capacity(new_capacity);
      m_.set_back_idx(m_.back_idx - m_.front_idx + buffer_offset);
      m_.set_front_idx(buffer_offset);

      BOOST_ASSERT(invariants_ok());
   }

   template <typename ForwardIterator>
   iterator insert_range(const_iterator position, ForwardIterator first, ForwardIterator last)
   {
      size_type n = boost::container::iterator_distance(first, last);

      if (position == end() && back_free_capacity() >= n) {// fast path
         iterator r(this->end());
         boost::container::uninitialized_copy_alloc(get_allocator_ref(), first, last, this->raw_end());
         m_.set_back_idx(m_.back_idx + n);
         return r;
      }
      else if (position == begin() && front_free_capacity() >= n) { // secondary fast path
         boost::container::uninitialized_copy_alloc(get_allocator_ref(), first, last, this->raw_begin() - n);
         m_.set_front_idx(m_.front_idx - n);
         return begin();
      }
      else {
         return insert_range_slow_path(position, first, last);
      }
   }

   template <typename ForwardIterator>
   iterator insert_range_slow_path(const_iterator position, ForwardIterator first, ForwardIterator last)
   {
      size_type n = boost::container::iterator_distance(first, last);
      size_type index = position - begin();

      if (front_free_capacity() + back_free_capacity() >= n) {
         // if we move enough, it can be done without reallocation

         iterator middle = begin() + index;
         n -= insert_range_slow_path_near_front(middle, first, n);

         if (n) {
            insert_range_slow_path_near_back(middle, first, n);
         }

         BOOST_ASSERT(first == last);
         return begin() + index;
      }
      else {
         const bool prefer_move_front = 2 * index <= size();
         return insert_range_reallocating_slow_path(prefer_move_front, index, first, n);
      }
   }

   template <typename Iterator>
   size_type insert_range_slow_path_near_front(iterator position, Iterator& first, size_type n)
   {
      size_type n_front = dtl::min_value(front_free_capacity(), n);
      iterator new_begin = begin() - n_front;
      iterator ctr_pos = new_begin;
      detail::construction_guard<allocator_type> ctr_guard(ctr_pos, get_allocator_ref());

      while (ctr_pos != begin()) {
         this->alloc_construct(ctr_pos++, *(first++));
         ctr_guard.extend();
      }

      boost::movelib::rotate_gcd(new_begin, ctr_pos, position);
      m_.set_front_idx(m_.front_idx - n_front);

      ctr_guard.release();

      BOOST_ASSERT(invariants_ok());

      return n_front;
   }

   template <typename Iterator>
   size_type insert_range_slow_path_near_back(iterator position, Iterator& first, size_type n)
   {
      const size_type n_back = dtl::min_value(back_free_capacity(), n);
      iterator ctr_pos = end();

      detail::construction_guard<allocator_type> ctr_guard(ctr_pos, get_allocator_ref());

      for (size_type i = 0; i < n_back; ++i) {
         this->alloc_construct(ctr_pos++, *first++);
         ctr_guard.extend();
      }

      boost::movelib::rotate_gcd(position, end(), ctr_pos);
      m_.set_back_idx(m_.back_idx + n_back);

      ctr_guard.release();

      BOOST_ASSERT(invariants_ok());

      return n_back;
   }

   template <typename Iterator>
   iterator insert_range_reallocating_slow_path
      (bool make_front_free, size_type new_elem_index, Iterator elems, size_type n)
   {
      // reallocate
      const size_type new_capacity = calculate_new_capacity(capacity() + n);
      pointer new_buffer = allocate(new_capacity);

      // guard allocation
      allocation_guard new_buffer_guard(new_buffer, new_capacity, get_allocator_ref());

      const size_type new_front_index = (make_front_free)
      ? new_capacity - back_free_capacity() - size() - n
      : m_.front_idx;

      const iterator new_begin = new_buffer + new_front_index;
      const iterator new_position = new_begin + new_elem_index;
      const iterator old_position = begin() + new_elem_index;

      // construct new element (and guard it)
      iterator second_half_position = new_position;
      detail::construction_guard<allocator_type> second_half_guard(second_half_position, get_allocator_ref());

      for (size_type i = 0; i < n; ++i) {
         this->alloc_construct(second_half_position++, *(elems++));
         second_half_guard.extend();
      }

      // move front-pos (possibly guarded)
      detail::construction_guard<allocator_type> first_half_guard(new_begin, get_allocator_ref());
      opt_move_or_copy(begin(), old_position, new_begin, first_half_guard);

      // move pos+1-end (possibly guarded)
      opt_move_or_copy(old_position, end(), second_half_position, second_half_guard);

      // cleanup
      destroy_elements(begin(), end());
      deallocate_buffer();

      // release alloc and other guards
      second_half_guard.release();
      first_half_guard.release();
      new_buffer_guard.release();

      // rebind members
      m_.set_capacity(new_capacity);
      m_.buffer = new_buffer;
      m_.set_back_idx(new_front_index + size() + n);
      m_.set_front_idx(new_front_index);

      return new_position;
   }

   template <typename Iterator>
   void construct_from_range(Iterator begin, Iterator end)
   {
      allocation_guard buffer_guard(m_.buffer, m_.capacity, get_allocator_ref());
      opt_copy(begin, end, m_.buffer);

      buffer_guard.release();
   }

   template <typename ForwardIterator>
   void allocate_and_copy_range(ForwardIterator first, ForwardIterator last)
   {
      size_type n = boost::container::iterator_distance(first, last);

      pointer new_buffer = n ? allocate(n) : pointer();
      allocation_guard new_buffer_guard(new_buffer, n, get_allocator_ref());

      opt_copy(first, last, new_buffer);

      destroy_elements(begin(), end());
      deallocate_buffer();

      m_.set_capacity(n);
      m_.buffer = new_buffer;
      m_.front_idx = 0;
      m_.set_back_idx(n);

      new_buffer_guard.release();
   }

   static void swap_big_big(devector& a, devector& b) BOOST_NOEXCEPT
   {
      boost::adl_move_swap(a.m_.capacity, b.m_.capacity);
      boost::adl_move_swap(a.m_.buffer, b.m_.buffer);
   }

   template <typename ForwardIterator>
   void overwrite_buffer_impl(ForwardIterator first, ForwardIterator last, dtl::true_)
   {
      const size_type n = boost::container::iterator_distance(first, last);

      BOOST_ASSERT(capacity() >= n);
      boost::container::uninitialized_copy_alloc_n
         ( get_allocator_ref(), boost::movelib::iterator_to_raw_pointer(first)
         , n, boost::movelib::iterator_to_raw_pointer(m_.buffer));
      m_.front_idx = 0;
      m_.set_back_idx(n);
   }

   template <typename InputIterator>
   InputIterator overwrite_buffer_impl(InputIterator first, InputIterator last, dtl::false_)
   {
      pointer pos = m_.buffer;
      detail::construction_guard<allocator_type> front_guard(pos, get_allocator_ref());

      while (first != last && pos != begin()) {
         this->alloc_construct(pos++, *first++);
         front_guard.extend();
      }

      while (first != last && pos != end()) {
         *pos++ = *first++;
      }

      detail::construction_guard<allocator_type> back_guard(pos, get_allocator_ref());

      iterator capacity_end = m_.buffer + capacity();
      while (first != last && pos != capacity_end) {
         this->alloc_construct(pos++, *first++);
         back_guard.extend();
      }

      pointer destroy_after = dtl::min_value(dtl::max_value(begin(), pos), end());
      destroy_elements(destroy_after, end());

      front_guard.release();
      back_guard.release();

      m_.front_idx = 0;
      m_.set_back_idx(pos - begin());
      return first;
   }

   template <typename ForwardIterator>
   BOOST_CONTAINER_FORCEINLINE void overwrite_buffer(ForwardIterator first, ForwardIterator last)
   {
      this->overwrite_buffer_impl(first, last,
         dtl::bool_<dtl::is_trivially_destructible<T>::value>());
   }

   bool invariants_ok()
   {
      return   (!m_.capacity || m_.buffer)
               && m_.front_idx <= m_.back_idx
               && m_.back_idx <= m_.capacity;
   }

   struct impl : allocator_type
   {
      impl()
         : allocator_type(), buffer(), front_idx(), back_idx(), capacity()
         #ifdef BOOST_CONTAINER_DEVECTOR_ALLOC_STATS
         , capacity_alloc_count()
         #endif
      {}

      explicit impl(const allocator_type &a)
         : allocator_type(a), buffer(), front_idx(), back_idx(), capacity()
         #ifdef BOOST_CONTAINER_DEVECTOR_ALLOC_STATS
         , capacity_alloc_count()
         #endif
      {}

      impl(const allocator_type &a, pointer p, size_type f, size_type b, size_type c)
         : allocator_type(a), buffer(p)
         //static cast sizes, as the allocation function will take care of overflows
         , front_idx(static_cast<stored_size_type>(f))
         , back_idx(static_cast<stored_size_type>(b))
         , capacity(static_cast<stored_size_type>(c))
         #ifdef BOOST_CONTAINER_DEVECTOR_ALLOC_STATS
         , capacity_alloc_count()
         #endif
      {}

      impl(BOOST_RV_REF(allocator_type) a, pointer p, size_type f, size_type b, size_type c)
         : allocator_type(boost::move(a)), buffer(p)
         //static cast sizes, as the allocation function will take care of overflows
         , front_idx(static_cast<stored_size_type>(f))
         , back_idx(static_cast<stored_size_type>(b))
         , capacity(static_cast<stored_size_type>(c))
         #ifdef BOOST_CONTAINER_DEVECTOR_ALLOC_STATS
         , capacity_alloc_count()
         #endif
      {}

      void set_back_idx(size_type bi)
      {  back_idx = static_cast<stored_size_type>(bi);}

      void set_front_idx(size_type fi)
      {  front_idx = static_cast<stored_size_type>(fi);}

      void set_capacity(size_type c)
      {  capacity = static_cast<stored_size_type>(c);}

      pointer          buffer;
      stored_size_type front_idx;
      stored_size_type back_idx;
      stored_size_type capacity;
      #ifdef BOOST_CONTAINER_DEVECTOR_ALLOC_STATS
      size_type capacity_alloc_count;
      #endif
   } m_;


   #ifdef BOOST_CONTAINER_DEVECTOR_ALLOC_STATS
   public:
   void reset_alloc_stats()
   {
      m_.capacity_alloc_count = 0;
   }

   size_type get_alloc_count() const
   {
      return m_.capacity_alloc_count;
   }

   #endif // ifdef BOOST_CONTAINER_DEVECTOR_ALLOC_STATS

   #endif // ifndef BOOST_CONTAINER_DOXYGEN_INVOKED
};

}} // namespace boost::container

#include <boost/container/detail/config_end.hpp>

#endif // BOOST_CONTAINER_DEVECTOR_HPP