/storage/packages/gcc/5.3.0/include/c++/5.3.0/bits/unordered_map.h

// unordered_map implementation -*- C++ -*-

// Copyright (C) 2010-2015 Free Software Foundation, Inc.

//

// This file is part of the GNU ISO C++ Library.  This library is free

// software; you can redistribute it and/or modify it under the

// terms of the GNU General Public License as published by the

// Free Software Foundation; either version 3, or (at your option)

// any later version.

// This library is distributed in the hope that it will be useful,

// but WITHOUT ANY WARRANTY; without even the implied warranty of

// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

// GNU General Public License for more details.

// Under Section 7 of GPL version 3, you are granted additional

// permissions described in the GCC Runtime Library Exception, version

// 3.1, as published by the Free Software Foundation.

// You should have received a copy of the GNU General Public License and

// a copy of the GCC Runtime Library Exception along with this program;

// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see

// <http://www.gnu.org/licenses/>.

/** @file bits/unordered_map.h

 *  This is an internal header file, included by other library headers.

 *  Do not attempt to use it directly. @headername{unordered_map}

 */

#ifndef _UNORDERED_MAP_H

#define _UNORDERED_MAP_H

namespace std _GLIBCXX_VISIBILITY(default)

{

_GLIBCXX_BEGIN_NAMESPACE_CONTAINER

  /// Base types for unordered_map.

  template<bool _Cache>

    using __umap_traits = __detail::_Hashtable_traits<_Cache, false, true>;

  template<typename _Key,

	   typename _Tp,

	   typename _Hash = hash<_Key>,

	   typename _Pred = std::equal_to<_Key>,

	   typename _Alloc = std::allocator<std::pair<const _Key, _Tp> >,

	   typename _Tr = __umap_traits<__cache_default<_Key, _Hash>::value>>

    using __umap_hashtable = _Hashtable<_Key, std::pair<const _Key, _Tp>,

                                        _Alloc, __detail::_Select1st,

				        _Pred, _Hash,

				        __detail::_Mod_range_hashing,

				        __detail::_Default_ranged_hash,

				        __detail::_Prime_rehash_policy, _Tr>;

  /// Base types for unordered_multimap.

  template<bool _Cache>

    using __ummap_traits = __detail::_Hashtable_traits<_Cache, false, false>;

  template<typename _Key,

	   typename _Tp,

	   typename _Hash = hash<_Key>,

	   typename _Pred = std::equal_to<_Key>,

	   typename _Alloc = std::allocator<std::pair<const _Key, _Tp> >,

	   typename _Tr = __ummap_traits<__cache_default<_Key, _Hash>::value>>

    using __ummap_hashtable = _Hashtable<_Key, std::pair<const _Key, _Tp>,

					 _Alloc, __detail::_Select1st,

					 _Pred, _Hash,

					 __detail::_Mod_range_hashing,

					 __detail::_Default_ranged_hash,

					 __detail::_Prime_rehash_policy, _Tr>;

  /**

   *  @brief A standard container composed of unique keys (containing

   *  at most one of each key value) that associates values of another type

   *  with the keys.

   *

   *  @ingroup unordered_associative_containers

   *

   *  @tparam  _Key    Type of key objects.

   *  @tparam  _Tp     Type of mapped objects.

   *  @tparam  _Hash   Hashing function object type, defaults to hash<_Value>.

   *  @tparam  _Pred   Predicate function object type, defaults

   *                   to equal_to<_Value>.

   *  @tparam  _Alloc  Allocator type, defaults to 

   *                   std::allocator<std::pair<const _Key, _Tp>>.

   *

   *  Meets the requirements of a <a href="tables.html#65">container</a>, and

   *  <a href="tables.html#xx">unordered associative container</a>

   *

   * The resulting value type of the container is std::pair<const _Key, _Tp>.

   *

   *  Base is _Hashtable, dispatched at compile time via template

   *  alias __umap_hashtable.

   */

  template<class _Key, class _Tp,

	   class _Hash = hash<_Key>,

	   class _Pred = std::equal_to<_Key>,

	   class _Alloc = std::allocator<std::pair<const _Key, _Tp> > >

    class unordered_map

    {

      typedef __umap_hashtable<_Key, _Tp, _Hash, _Pred, _Alloc>  _Hashtable;

      _Hashtable _M_h;

    public:

      // typedefs:

      //@{

      /// Public typedefs.

      typedef typename _Hashtable::key_type	key_type;

      typedef typename _Hashtable::value_type	value_type;

      typedef typename _Hashtable::mapped_type	mapped_type;

      typedef typename _Hashtable::hasher	hasher;

      typedef typename _Hashtable::key_equal	key_equal;

      typedef typename _Hashtable::allocator_type allocator_type;

      //@}

      //@{

      ///  Iterator-related typedefs.

      typedef typename _Hashtable::pointer		pointer;

      typedef typename _Hashtable::const_pointer	const_pointer;

      typedef typename _Hashtable::reference		reference;

      typedef typename _Hashtable::const_reference	const_reference;

      typedef typename _Hashtable::iterator		iterator;

      typedef typename _Hashtable::const_iterator	const_iterator;

      typedef typename _Hashtable::local_iterator	local_iterator;

      typedef typename _Hashtable::const_local_iterator	const_local_iterator;

      typedef typename _Hashtable::size_type		size_type;

      typedef typename _Hashtable::difference_type	difference_type;

      //@}

      //construct/destroy/copy

      /// Default constructor.

      unordered_map() = default;

      /**

       *  @brief  Default constructor creates no elements.

       *  @param __n  Minimal initial number of buckets.

       *  @param __hf  A hash functor.

       *  @param __eql  A key equality functor.

       *  @param __a  An allocator object.

       */

      explicit

      unordered_map(size_type __n,

		    const hasher& __hf = hasher(),

		    const key_equal& __eql = key_equal(),

		    const allocator_type& __a = allocator_type())

      : _M_h(__n, __hf, __eql, __a)

      { }

      /**

       *  @brief  Builds an %unordered_map from a range.

       *  @param  __first  An input iterator.

       *  @param  __last  An input iterator.

       *  @param __n  Minimal initial number of buckets.

       *  @param __hf  A hash functor.

       *  @param __eql  A key equality functor.

       *  @param __a  An allocator object.

       *

       *  Create an %unordered_map consisting of copies of the elements from

       *  [__first,__last).  This is linear in N (where N is

       *  distance(__first,__last)).

       */

      template<typename _InputIterator>

	unordered_map(_InputIterator __first, _InputIterator __last,

		      size_type __n = 0,

		      const hasher& __hf = hasher(),

		      const key_equal& __eql = key_equal(),

		      const allocator_type& __a = allocator_type())

	: _M_h(__first, __last, __n, __hf, __eql, __a)

	{ }

      /// Copy constructor.

      unordered_map(const unordered_map&) = default;

      /// Move constructor.

      unordered_map(unordered_map&&) = default;

      /**

       *  @brief Creates an %unordered_map with no elements.

       *  @param __a An allocator object.

       */

      explicit

      unordered_map(const allocator_type& __a)

	: _M_h(__a)

      { }

      /*

       *  @brief Copy constructor with allocator argument.

       * @param  __uset  Input %unordered_map to copy.

       * @param  __a  An allocator object.

       */

      unordered_map(const unordered_map& __umap,

		    const allocator_type& __a)

      : _M_h(__umap._M_h, __a)

      { }

      /*

       *  @brief  Move constructor with allocator argument.

       *  @param  __uset Input %unordered_map to move.

       *  @param  __a    An allocator object.

       */

      unordered_map(unordered_map&& __umap,

		    const allocator_type& __a)

      : _M_h(std::move(__umap._M_h), __a)

      { }

      /**

       *  @brief  Builds an %unordered_map from an initializer_list.

       *  @param  __l  An initializer_list.

       *  @param __n  Minimal initial number of buckets.

       *  @param __hf  A hash functor.

       *  @param __eql  A key equality functor.

       *  @param  __a  An allocator object.

       *

       *  Create an %unordered_map consisting of copies of the elements in the

       *  list. This is linear in N (where N is @a __l.size()).

       */

      unordered_map(initializer_list<value_type> __l,

		    size_type __n = 0,

		    const hasher& __hf = hasher(),

		    const key_equal& __eql = key_equal(),

		    const allocator_type& __a = allocator_type())

      : _M_h(__l, __n, __hf, __eql, __a)

      { }

      unordered_map(size_type __n, const allocator_type& __a)

      : unordered_map(__n, hasher(), key_equal(), __a)

      { }

      unordered_map(size_type __n, const hasher& __hf,

		    const allocator_type& __a)

      : unordered_map(__n, __hf, key_equal(), __a)

      { }

      template<typename _InputIterator>

	unordered_map(_InputIterator __first, _InputIterator __last,

		      size_type __n,

		      const allocator_type& __a)

	: unordered_map(__first, __last, __n, hasher(), key_equal(), __a)

	{ }

      template<typename _InputIterator>

	unordered_map(_InputIterator __first, _InputIterator __last,

		      size_type __n, const hasher& __hf,

		      const allocator_type& __a)

	  : unordered_map(__first, __last, __n, __hf, key_equal(), __a)

	{ }

      unordered_map(initializer_list<value_type> __l,

		    size_type __n,

		    const allocator_type& __a)

      : unordered_map(__l, __n, hasher(), key_equal(), __a)

      { }

      unordered_map(initializer_list<value_type> __l,

		    size_type __n, const hasher& __hf,

		    const allocator_type& __a)

      : unordered_map(__l, __n, __hf, key_equal(), __a)

      { }

      /// Copy assignment operator.

      unordered_map&

      operator=(const unordered_map&) = default;

      /// Move assignment operator.

      unordered_map&

      operator=(unordered_map&&) = default;

      /**

       *  @brief  %Unordered_map list assignment operator.

       *  @param  __l  An initializer_list.

       *

       *  This function fills an %unordered_map with copies of the elements in

       *  the initializer list @a __l.

       *

       *  Note that the assignment completely changes the %unordered_map and

       *  that the resulting %unordered_map's size is the same as the number

       *  of elements assigned.  Old data may be lost.

       */

      unordered_map&

      operator=(initializer_list<value_type> __l)

      {

	_M_h = __l;

	return *this;

      }

      ///  Returns the allocator object with which the %unordered_map was

      ///  constructed.

      allocator_type

      get_allocator() const noexcept

      { return _M_h.get_allocator(); }

      // size and capacity:

      ///  Returns true if the %unordered_map is empty.

      bool

      empty() const noexcept

      { return _M_h.empty(); }

      ///  Returns the size of the %unordered_map.

      size_type

      size() const noexcept

      { return _M_h.size(); }

      ///  Returns the maximum size of the %unordered_map.

      size_type

      max_size() const noexcept

      { return _M_h.max_size(); }

      // iterators.

      /**

       *  Returns a read/write iterator that points to the first element in the

       *  %unordered_map.

       */

      iterator

      begin() noexcept

      { return _M_h.begin(); }

      //@{

      /**

       *  Returns a read-only (constant) iterator that points to the first

       *  element in the %unordered_map.

       */

      const_iterator

      begin() const noexcept

      { return _M_h.begin(); }

      const_iterator

      cbegin() const noexcept

      { return _M_h.begin(); }

      //@}

      /**

       *  Returns a read/write iterator that points one past the last element in

       *  the %unordered_map.

       */

      iterator

      end() noexcept

      { return _M_h.end(); }

      //@{

      /**

       *  Returns a read-only (constant) iterator that points one past the last

       *  element in the %unordered_map.

       */

      const_iterator

      end() const noexcept

      { return _M_h.end(); }

      const_iterator

      cend() const noexcept

      { return _M_h.end(); }

      //@}

      // modifiers.

      /**

       *  @brief Attempts to build and insert a std::pair into the

       *  %unordered_map.

       *

       *  @param __args  Arguments used to generate a new pair instance (see

       *	        std::piecewise_contruct for passing arguments to each

       *	        part of the pair constructor).

       *

       *  @return  A pair, of which the first element is an iterator that points

       *           to the possibly inserted pair, and the second is a bool that

       *           is true if the pair was actually inserted.

       *

       *  This function attempts to build and insert a (key, value) %pair into

       *  the %unordered_map.

       *  An %unordered_map relies on unique keys and thus a %pair is only

       *  inserted if its first element (the key) is not already present in the

       *  %unordered_map.

       *

       *  Insertion requires amortized constant time.

       */

      template<typename... _Args>

	std::pair<iterator, bool>

	emplace(_Args&&... __args)

	{ return _M_h.emplace(std::forward<_Args>(__args)...); }

      /**

       *  @brief Attempts to build and insert a std::pair into the

       *  %unordered_map.

       *

       *  @param  __pos  An iterator that serves as a hint as to where the pair

       *                should be inserted.

       *  @param  __args  Arguments used to generate a new pair instance (see

       *	         std::piecewise_contruct for passing arguments to each

       *	         part of the pair constructor).

       *  @return An iterator that points to the element with key of the

       *          std::pair built from @a __args (may or may not be that

       *          std::pair).

       *

       *  This function is not concerned about whether the insertion took place,

       *  and thus does not return a boolean like the single-argument emplace()

       *  does.

       *  Note that the first parameter is only a hint and can potentially

       *  improve the performance of the insertion process. A bad hint would

       *  cause no gains in efficiency.

       *

       *  See

       *  https://gcc.gnu.org/onlinedocs/libstdc++/manual/associative.html#containers.associative.insert_hints

       *  for more on @a hinting.

       *

       *  Insertion requires amortized constant time.

       */

      template<typename... _Args>

	iterator

	emplace_hint(const_iterator __pos, _Args&&... __args)

	{ return _M_h.emplace_hint(__pos, std::forward<_Args>(__args)...); }

      //@{

      /**

       *  @brief Attempts to insert a std::pair into the %unordered_map.

       *  @param __x Pair to be inserted (see std::make_pair for easy

       *	     creation of pairs).

       *

       *  @return  A pair, of which the first element is an iterator that 

       *           points to the possibly inserted pair, and the second is 

       *           a bool that is true if the pair was actually inserted.

       *

       *  This function attempts to insert a (key, value) %pair into the

       *  %unordered_map. An %unordered_map relies on unique keys and thus a

       *  %pair is only inserted if its first element (the key) is not already

       *  present in the %unordered_map.

       *

       *  Insertion requires amortized constant time.

       */

      std::pair<iterator, bool>

      insert(const value_type& __x)

      { return _M_h.insert(__x); }

      template<typename _Pair, typename = typename

	       std::enable_if<std::is_constructible<value_type,

						    _Pair&&>::value>::type>

	std::pair<iterator, bool>

	insert(_Pair&& __x)

        { return _M_h.insert(std::forward<_Pair>(__x)); }

      //@}

      //@{

      /**

       *  @brief Attempts to insert a std::pair into the %unordered_map.

       *  @param  __hint  An iterator that serves as a hint as to where the

       *                 pair should be inserted.

       *  @param  __x  Pair to be inserted (see std::make_pair for easy creation

       *               of pairs).

       *  @return An iterator that points to the element with key of

       *           @a __x (may or may not be the %pair passed in).

       *

       *  This function is not concerned about whether the insertion took place,

       *  and thus does not return a boolean like the single-argument insert()

       *  does.  Note that the first parameter is only a hint and can

       *  potentially improve the performance of the insertion process.  A bad

       *  hint would cause no gains in efficiency.

       *

       *  See

       *  https://gcc.gnu.org/onlinedocs/libstdc++/manual/associative.html#containers.associative.insert_hints

       *  for more on @a hinting.

       *

       *  Insertion requires amortized constant time.

       */

      iterator

      insert(const_iterator __hint, const value_type& __x)

      { return _M_h.insert(__hint, __x); }

      template<typename _Pair, typename = typename

	       std::enable_if<std::is_constructible<value_type,

						    _Pair&&>::value>::type>

	iterator

	insert(const_iterator __hint, _Pair&& __x)

	{ return _M_h.insert(__hint, std::forward<_Pair>(__x)); }

      //@}

      /**

       *  @brief A template function that attempts to insert a range of

       *  elements.

       *  @param  __first  Iterator pointing to the start of the range to be

       *                   inserted.

       *  @param  __last  Iterator pointing to the end of the range.

       *

       *  Complexity similar to that of the range constructor.

       */

      template<typename _InputIterator>

	void

	insert(_InputIterator __first, _InputIterator __last)

	{ _M_h.insert(__first, __last); }

      /**

       *  @brief Attempts to insert a list of elements into the %unordered_map.

       *  @param  __l  A std::initializer_list<value_type> of elements

       *               to be inserted.

       *

       *  Complexity similar to that of the range constructor.

       */

      void

      insert(initializer_list<value_type> __l)

      { _M_h.insert(__l); }

      //@{

      /**

       *  @brief Erases an element from an %unordered_map.

       *  @param  __position  An iterator pointing to the element to be erased.

       *  @return An iterator pointing to the element immediately following

       *          @a __position prior to the element being erased. If no such

       *          element exists, end() is returned.

       *

       *  This function erases an element, pointed to by the given iterator,

       *  from an %unordered_map.

       *  Note that this function only erases the element, and that if the

       *  element is itself a pointer, the pointed-to memory is not touched in

       *  any way.  Managing the pointer is the user's responsibility.

       */

      iterator

      erase(const_iterator __position)

      { return _M_h.erase(__position); }

      // LWG 2059.

      iterator

      erase(iterator __position)

      { return _M_h.erase(__position); }

      //@}

      /**

       *  @brief Erases elements according to the provided key.

       *  @param  __x  Key of element to be erased.

       *  @return  The number of elements erased.

       *

       *  This function erases all the elements located by the given key from

       *  an %unordered_map. For an %unordered_map the result of this function

       *  can only be 0 (not present) or 1 (present).

       *  Note that this function only erases the element, and that if the

       *  element is itself a pointer, the pointed-to memory is not touched in

       *  any way.  Managing the pointer is the user's responsibility.

       */

      size_type

      erase(const key_type& __x)

      { return _M_h.erase(__x); }

      /**

       *  @brief Erases a [__first,__last) range of elements from an

       *  %unordered_map.

       *  @param  __first  Iterator pointing to the start of the range to be

       *                  erased.

       *  @param __last  Iterator pointing to the end of the range to

       *                be erased.

       *  @return The iterator @a __last.

       *

       *  This function erases a sequence of elements from an %unordered_map.

       *  Note that this function only erases the elements, and that if

       *  the element is itself a pointer, the pointed-to memory is not touched

       *  in any way.  Managing the pointer is the user's responsibility.

       */

      iterator

      erase(const_iterator __first, const_iterator __last)

      { return _M_h.erase(__first, __last); }

      /**

       *  Erases all elements in an %unordered_map.

       *  Note that this function only erases the elements, and that if the

       *  elements themselves are pointers, the pointed-to memory is not touched

       *  in any way.  Managing the pointer is the user's responsibility.

       */

      void

      clear() noexcept

      { _M_h.clear(); }

      /**

       *  @brief  Swaps data with another %unordered_map.

       *  @param  __x  An %unordered_map of the same element and allocator

       *  types.

       *

       *  This exchanges the elements between two %unordered_map in constant

       *  time.

       *  Note that the global std::swap() function is specialized such that

       *  std::swap(m1,m2) will feed to this function.

       */

      void

      swap(unordered_map& __x)

      noexcept( noexcept(_M_h.swap(__x._M_h)) )

      { _M_h.swap(__x._M_h); }

      // observers.

      ///  Returns the hash functor object with which the %unordered_map was

      ///  constructed.

      hasher

      hash_function() const

      { return _M_h.hash_function(); }

      ///  Returns the key comparison object with which the %unordered_map was

      ///  constructed.

      key_equal

      key_eq() const

      { return _M_h.key_eq(); }

      // lookup.

      //@{

      /**

       *  @brief Tries to locate an element in an %unordered_map.

       *  @param  __x  Key to be located.

       *  @return  Iterator pointing to sought-after element, or end() if not

       *           found.

       *

       *  This function takes a key and tries to locate the element with which

       *  the key matches.  If successful the function returns an iterator

       *  pointing to the sought after element.  If unsuccessful it returns the

       *  past-the-end ( @c end() ) iterator.

       */

      iterator

      find(const key_type& __x)

      { return _M_h.find(__x); }

      const_iterator

      find(const key_type& __x) const

      { return _M_h.find(__x); }

      //@}

      /**

       *  @brief  Finds the number of elements.

       *  @param  __x  Key to count.

       *  @return  Number of elements with specified key.

       *

       *  This function only makes sense for %unordered_multimap; for

       *  %unordered_map the result will either be 0 (not present) or 1

       *  (present).

       */

      size_type

      count(const key_type& __x) const

      { return _M_h.count(__x); }

      //@{

      /**

       *  @brief Finds a subsequence matching given key.

       *  @param  __x  Key to be located.

       *  @return  Pair of iterators that possibly points to the subsequence

       *           matching given key.

       *

       *  This function probably only makes sense for %unordered_multimap.

       */

      std::pair<iterator, iterator>

      equal_range(const key_type& __x)

      { return _M_h.equal_range(__x); }

      std::pair<const_iterator, const_iterator>

      equal_range(const key_type& __x) const

      { return _M_h.equal_range(__x); }

      //@}

      //@{

      /**

       *  @brief  Subscript ( @c [] ) access to %unordered_map data.

       *  @param  __k  The key for which data should be retrieved.

       *  @return  A reference to the data of the (key,data) %pair.

       *

       *  Allows for easy lookup with the subscript ( @c [] )operator.  Returns

       *  data associated with the key specified in subscript.  If the key does

       *  not exist, a pair with that key is created using default values, which

       *  is then returned.

       *

       *  Lookup requires constant time.

       */

      mapped_type&

      operator[](const key_type& __k)

      { return _M_h[__k]; }

      mapped_type&

      operator[](key_type&& __k)

      { return _M_h[std::move(__k)]; }

      //@}

      //@{

      /**

       *  @brief  Access to %unordered_map data.

       *  @param  __k  The key for which data should be retrieved.

       *  @return  A reference to the data whose key is equal to @a __k, if

       *           such a data is present in the %unordered_map.

       *  @throw  std::out_of_range  If no such data is present.

       */

      mapped_type&

      at(const key_type& __k)

      { return _M_h.at(__k); }

      const mapped_type&

      at(const key_type& __k) const

      { return _M_h.at(__k); }

      //@}

      // bucket interface.

      /// Returns the number of buckets of the %unordered_map.

      size_type

      bucket_count() const noexcept

      { return _M_h.bucket_count(); }

      /// Returns the maximum number of buckets of the %unordered_map.

      size_type

      max_bucket_count() const noexcept

      { return _M_h.max_bucket_count(); }

      /*

       * @brief  Returns the number of elements in a given bucket.

       * @param  __n  A bucket index.

       * @return  The number of elements in the bucket.

       */

      size_type

      bucket_size(size_type __n) const

      { return _M_h.bucket_size(__n); }

      /*

       * @brief  Returns the bucket index of a given element.

       * @param  __key  A key instance.

       * @return  The key bucket index.

       */

      size_type

      bucket(const key_type& __key) const

      { return _M_h.bucket(__key); }

      /**

       *  @brief  Returns a read/write iterator pointing to the first bucket

       *         element.

       *  @param  __n The bucket index.

       *  @return  A read/write local iterator.

       */

      local_iterator

      begin(size_type __n)

      { return _M_h.begin(__n); }

      //@{

      /**

       *  @brief  Returns a read-only (constant) iterator pointing to the first

       *         bucket element.

       *  @param  __n The bucket index.

       *  @return  A read-only local iterator.

       */

      const_local_iterator

      begin(size_type __n) const

      { return _M_h.begin(__n); }

      const_local_iterator

      cbegin(size_type __n) const

      { return _M_h.cbegin(__n); }

      //@}

      /**

       *  @brief  Returns a read/write iterator pointing to one past the last

       *         bucket elements.

       *  @param  __n The bucket index.

       *  @return  A read/write local iterator.

       */

      local_iterator

      end(size_type __n)

      { return _M_h.end(__n); }

      //@{

      /**

       *  @brief  Returns a read-only (constant) iterator pointing to one past

       *         the last bucket elements.

       *  @param  __n The bucket index.

       *  @return  A read-only local iterator.

       */

      const_local_iterator

      end(size_type __n) const

      { return _M_h.end(__n); }

      const_local_iterator

      cend(size_type __n) const

      { return _M_h.cend(__n); }

      //@}

      // hash policy.

      /// Returns the average number of elements per bucket.

      float

      load_factor() const noexcept

      { return _M_h.load_factor(); }

      /// Returns a positive number that the %unordered_map tries to keep the

      /// load factor less than or equal to.

      float

      max_load_factor() const noexcept

      { return _M_h.max_load_factor(); }

      /**

       *  @brief  Change the %unordered_map maximum load factor.

       *  @param  __z The new maximum load factor.

       */

      void

      max_load_factor(float __z)

      { _M_h.max_load_factor(__z); }

      /**

       *  @brief  May rehash the %unordered_map.

       *  @param  __n The new number of buckets.

       *

       *  Rehash will occur only if the new number of buckets respect the

       *  %unordered_map maximum load factor.

       */

      void

      rehash(size_type __n)

      { _M_h.rehash(__n); }

      /**

       *  @brief  Prepare the %unordered_map for a specified number of

       *          elements.

       *  @param  __n Number of elements required.

       *

       *  Same as rehash(ceil(n / max_load_factor())).

       */

      void

      reserve(size_type __n)

      { _M_h.reserve(__n); }

      template<typename _Key1, typename _Tp1, typename _Hash1, typename _Pred1,

	       typename _Alloc1>

        friend bool

      operator==(const unordered_map<_Key1, _Tp1, _Hash1, _Pred1, _Alloc1>&,

		 const unordered_map<_Key1, _Tp1, _Hash1, _Pred1, _Alloc1>&);

    };

  /**

   *  @brief A standard container composed of equivalent keys

   *  (possibly containing multiple of each key value) that associates

   *  values of another type with the keys.

   *

   *  @ingroup unordered_associative_containers

   *

   *  @tparam  _Key    Type of key objects.

   *  @tparam  _Tp     Type of mapped objects.

   *  @tparam  _Hash   Hashing function object type, defaults to hash<_Value>.

   *  @tparam  _Pred   Predicate function object type, defaults

   *                   to equal_to<_Value>.

   *  @tparam  _Alloc  Allocator type, defaults to

   *                   std::allocator<std::pair<const _Key, _Tp>>.

   *

   *  Meets the requirements of a <a href="tables.html#65">container</a>, and

   *  <a href="tables.html#xx">unordered associative container</a>

   *

   * The resulting value type of the container is std::pair<const _Key, _Tp>.

   *

   *  Base is _Hashtable, dispatched at compile time via template

   *  alias __ummap_hashtable.

   */

  template<class _Key, class _Tp,

	   class _Hash = hash<_Key>,

	   class _Pred = std::equal_to<_Key>,

	   class _Alloc = std::allocator<std::pair<const _Key, _Tp> > >

    class unordered_multimap

    {

      typedef __ummap_hashtable<_Key, _Tp, _Hash, _Pred, _Alloc>  _Hashtable;

      _Hashtable _M_h;

    public:

      // typedefs:

      //@{

      /// Public typedefs.

      typedef typename _Hashtable::key_type	key_type;

      typedef typename _Hashtable::value_type	value_type;

      typedef typename _Hashtable::mapped_type	mapped_type;

      typedef typename _Hashtable::hasher	hasher;

      typedef typename _Hashtable::key_equal	key_equal;

      typedef typename _Hashtable::allocator_type allocator_type;

      //@}

      //@{

      ///  Iterator-related typedefs.

      typedef typename _Hashtable::pointer		pointer;

      typedef typename _Hashtable::const_pointer	const_pointer;

      typedef typename _Hashtable::reference		reference;

      typedef typename _Hashtable::const_reference	const_reference;

      typedef typename _Hashtable::iterator		iterator;

      typedef typename _Hashtable::const_iterator	const_iterator;

      typedef typename _Hashtable::local_iterator	local_iterator;

      typedef typename _Hashtable::const_local_iterator	const_local_iterator;

      typedef typename _Hashtable::size_type		size_type;

      typedef typename _Hashtable::difference_type	difference_type;

      //@}

      //construct/destroy/copy

      /// Default constructor.

      unordered_multimap() = default;

      /**

       *  @brief  Default constructor creates no elements.

       *  @param __n  Mnimal initial number of buckets.

       *  @param __hf  A hash functor.

       *  @param __eql  A key equality functor.

       *  @param __a  An allocator object.

       */

      explicit

      unordered_multimap(size_type __n,

			 const hasher& __hf = hasher(),

			 const key_equal& __eql = key_equal(),

			 const allocator_type& __a = allocator_type())

      : _M_h(__n, __hf, __eql, __a)

      { }

      /**

       *  @brief  Builds an %unordered_multimap from a range.

       *  @param  __first An input iterator.

       *  @param  __last  An input iterator.

       *  @param __n      Minimal initial number of buckets.

       *  @param __hf     A hash functor.

       *  @param __eql    A key equality functor.

       *  @param __a      An allocator object.

       *

       *  Create an %unordered_multimap consisting of copies of the elements

       *  from [__first,__last).  This is linear in N (where N is

       *  distance(__first,__last)).

       */

      template<typename _InputIterator>

	unordered_multimap(_InputIterator __first, _InputIterator __last,

			   size_type __n = 0,

			   const hasher& __hf = hasher(),

			   const key_equal& __eql = key_equal(),

			   const allocator_type& __a = allocator_type())

	: _M_h(__first, __last, __n, __hf, __eql, __a)

	{ }

      /// Copy constructor.

      unordered_multimap(const unordered_multimap&) = default;

      /// Move constructor.

      unordered_multimap(unordered_multimap&&) = default;

      /**

       *  @brief Creates an %unordered_multimap with no elements.

       *  @param __a An allocator object.

       */

      explicit

      unordered_multimap(const allocator_type& __a)

      : _M_h(__a)

      { }

      /*

       *  @brief Copy constructor with allocator argument.

       * @param  __uset  Input %unordered_multimap to copy.

       * @param  __a  An allocator object.

       */

      unordered_multimap(const unordered_multimap& __ummap,

			 const allocator_type& __a)

      : _M_h(__ummap._M_h, __a)

      { }

      /*

       *  @brief  Move constructor with allocator argument.

       *  @param  __uset Input %unordered_multimap to move.

       *  @param  __a    An allocator object.

       */

      unordered_multimap(unordered_multimap&& __ummap,

			 const allocator_type& __a)

      : _M_h(std::move(__ummap._M_h), __a)

      { }

      /**

       *  @brief  Builds an %unordered_multimap from an initializer_list.

       *  @param  __l  An initializer_list.

       *  @param __n  Minimal initial number of buckets.

       *  @param __hf  A hash functor.

       *  @param __eql  A key equality functor.

       *  @param  __a  An allocator object.

       *

       *  Create an %unordered_multimap consisting of copies of the elements in

       *  the list. This is linear in N (where N is @a __l.size()).

       */

      unordered_multimap(initializer_list<value_type> __l,

			 size_type __n = 0,

			 const hasher& __hf = hasher(),

			 const key_equal& __eql = key_equal(),

			 const allocator_type& __a = allocator_type())

      : _M_h(__l, __n, __hf, __eql, __a)

      { }

      unordered_multimap(size_type __n, const allocator_type& __a)

      : unordered_multimap(__n, hasher(), key_equal(), __a)

      { }

      unordered_multimap(size_type __n, const hasher& __hf,

			 const allocator_type& __a)

      : unordered_multimap(__n, __hf, key_equal(), __a)

      { }

      template<typename _InputIterator>

	unordered_multimap(_InputIterator __first, _InputIterator __last,

			   size_type __n,

			   const allocator_type& __a)

	: unordered_multimap(__first, __last, __n, hasher(), key_equal(), __a)

	{ }

      template<typename _InputIterator>

	unordered_multimap(_InputIterator __first, _InputIterator __last,

			   size_type __n, const hasher& __hf,

			   const allocator_type& __a)

	: unordered_multimap(__first, __last, __n, __hf, key_equal(), __a)

	{ }

      unordered_multimap(initializer_list<value_type> __l,

			 size_type __n,

			 const allocator_type& __a)

      : unordered_multimap(__l, __n, hasher(), key_equal(), __a)

      { }

      unordered_multimap(initializer_list<value_type> __l,

			 size_type __n, const hasher& __hf,

			 const allocator_type& __a)

      : unordered_multimap(__l, __n, __hf, key_equal(), __a)

      { }

      /// Copy assignment operator.

      unordered_multimap&

      operator=(const unordered_multimap&) = default;

      /// Move assignment operator.

      unordered_multimap&

      operator=(unordered_multimap&&) = default;

      /**

       *  @brief  %Unordered_multimap list assignment operator.

       *  @param  __l  An initializer_list.

       *

       *  This function fills an %unordered_multimap with copies of the elements

       *  in the initializer list @a __l.

       *

       *  Note that the assignment completely changes the %unordered_multimap

       *  and that the resulting %unordered_multimap's size is the same as the

       *  number of elements assigned.  Old data may be lost.

       */

      unordered_multimap&

      operator=(initializer_list<value_type> __l)

      {

	_M_h = __l;

	return *this;

      }

      ///  Returns the allocator object with which the %unordered_multimap was

      ///  constructed.

      allocator_type

      get_allocator() const noexcept

      { return _M_h.get_allocator(); }

      // size and capacity:

      ///  Returns true if the %unordered_multimap is empty.

      bool

      empty() const noexcept

      { return _M_h.empty(); }

      ///  Returns the size of the %unordered_multimap.

      size_type

      size() const noexcept

      { return _M_h.size(); }

      ///  Returns the maximum size of the %unordered_multimap.

      size_type

      max_size() const noexcept

      { return _M_h.max_size(); }

      // iterators.

      /**

       *  Returns a read/write iterator that points to the first element in the

       *  %unordered_multimap.

       */

      iterator

      begin() noexcept

      { return _M_h.begin(); }

      //@{

      /**

       *  Returns a read-only (constant) iterator that points to the first

       *  element in the %unordered_multimap.

       */

      const_iterator

      begin() const noexcept

      { return _M_h.begin(); }

      const_iterator

      cbegin() const noexcept

      { return _M_h.begin(); }

      //@}

      /**

       *  Returns a read/write iterator that points one past the last element in

       *  the %unordered_multimap.

       */

      iterator

      end() noexcept

      { return _M_h.end(); }

      //@{

      /**

       *  Returns a read-only (constant) iterator that points one past the last

       *  element in the %unordered_multimap.

       */

      const_iterator

      end() const noexcept

      { return _M_h.end(); }

      const_iterator

      cend() const noexcept

      { return _M_h.end(); }

      //@}

      // modifiers.

      /**

       *  @brief Attempts to build and insert a std::pair into the

       *  %unordered_multimap.

       *

       *  @param __args  Arguments used to generate a new pair instance (see

       *	        std::piecewise_contruct for passing arguments to each

       *	        part of the pair constructor).

       *

       *  @return  An iterator that points to the inserted pair.

       *

       *  This function attempts to build and insert a (key, value) %pair into

       *  the %unordered_multimap.

       *

       *  Insertion requires amortized constant time.

       */

      template<typename... _Args>

	iterator

	emplace(_Args&&... __args)

	{ return _M_h.emplace(std::forward<_Args>(__args)...); }

      /**

       *  @brief Attempts to build and insert a std::pair into the

       *  %unordered_multimap.

       *

       *  @param  __pos  An iterator that serves as a hint as to where the pair

       *                should be inserted.

       *  @param  __args  Arguments used to generate a new pair instance (see

       *	         std::piecewise_contruct for passing arguments to each

       *	         part of the pair constructor).

       *  @return An iterator that points to the element with key of the

       *          std::pair built from @a __args.

       *

       *  Note that the first parameter is only a hint and can potentially

       *  improve the performance of the insertion process. A bad hint would

       *  cause no gains in efficiency.

       *

       *  See

       *  https://gcc.gnu.org/onlinedocs/libstdc++/manual/associative.html#containers.associative.insert_hints

       *  for more on @a hinting.

       *

       *  Insertion requires amortized constant time.

       */

      template<typename... _Args>

	iterator

	emplace_hint(const_iterator __pos, _Args&&... __args)

	{ return _M_h.emplace_hint(__pos, std::forward<_Args>(__args)...); }

      //@{

      /**

       *  @brief Inserts a std::pair into the %unordered_multimap.

       *  @param __x Pair to be inserted (see std::make_pair for easy

       *	     creation of pairs).

       *

       *  @return  An iterator that points to the inserted pair.

       *

       *  Insertion requires amortized constant time.

       */

      iterator

      insert(const value_type& __x)

      { return _M_h.insert(__x); }

      template<typename _Pair, typename = typename

	       std::enable_if<std::is_constructible<value_type,

						    _Pair&&>::value>::type>

	iterator

	insert(_Pair&& __x)

        { return _M_h.insert(std::forward<_Pair>(__x)); }

      //@}

      //@{

      /**

       *  @brief Inserts a std::pair into the %unordered_multimap.

       *  @param  __hint  An iterator that serves as a hint as to where the

       *                 pair should be inserted.

       *  @param  __x  Pair to be inserted (see std::make_pair for easy creation

       *               of pairs).

       *  @return An iterator that points to the element with key of

       *           @a __x (may or may not be the %pair passed in).

       *

       *  Note that the first parameter is only a hint and can potentially

       *  improve the performance of the insertion process.  A bad hint would

       *  cause no gains in efficiency.

       *

       *  See

       *  https://gcc.gnu.org/onlinedocs/libstdc++/manual/associative.html#containers.associative.insert_hints

       *  for more on @a hinting.

       *

       *  Insertion requires amortized constant time.

       */

      iterator

      insert(const_iterator __hint, const value_type& __x)

      { return _M_h.insert(__hint, __x); }

      template<typename _Pair, typename = typename

	       std::enable_if<std::is_constructible<value_type,

						    _Pair&&>::value>::type>

	iterator

	insert(const_iterator __hint, _Pair&& __x)

        { return _M_h.insert(__hint, std::forward<_Pair>(__x)); }

      //@}

      /**

       *  @brief A template function that attempts to insert a range of

       *  elements.

       *  @param  __first  Iterator pointing to the start of the range to be

       *                   inserted.

       *  @param  __last  Iterator pointing to the end of the range.

       *

       *  Complexity similar to that of the range constructor.

       */

      template<typename _InputIterator>

	void

	insert(_InputIterator __first, _InputIterator __last)

	{ _M_h.insert(__first, __last); }

      /**

       *  @brief Attempts to insert a list of elements into the

       *  %unordered_multimap.

       *  @param  __l  A std::initializer_list<value_type> of elements

       *               to be inserted.

       *

       *  Complexity similar to that of the range constructor.

       */

      void

      insert(initializer_list<value_type> __l)

      { _M_h.insert(__l); }

      //@{

      /**

       *  @brief Erases an element from an %unordered_multimap.

       *  @param  __position  An iterator pointing to the element to be erased.

       *  @return An iterator pointing to the element immediately following

       *          @a __position prior to the element being erased. If no such

       *          element exists, end() is returned.

       *

       *  This function erases an element, pointed to by the given iterator,

       *  from an %unordered_multimap.

       *  Note that this function only erases the element, and that if the

       *  element is itself a pointer, the pointed-to memory is not touched in

       *  any way.  Managing the pointer is the user's responsibility.

       */

      iterator

      erase(const_iterator __position)

      { return _M_h.erase(__position); }

      // LWG 2059.

      iterator

      erase(iterator __position)

      { return _M_h.erase(__position); }

      //@}

      /**

       *  @brief Erases elements according to the provided key.

       *  @param  __x  Key of elements to be erased.

       *  @return  The number of elements erased.

       *

       *  This function erases all the elements located by the given key from

       *  an %unordered_multimap.

       *  Note that this function only erases the element, and that if the

       *  element is itself a pointer, the pointed-to memory is not touched in

       *  any way.  Managing the pointer is the user's responsibility.

       */

      size_type

      erase(const key_type& __x)

      { return _M_h.erase(__x); }

      /**

       *  @brief Erases a [__first,__last) range of elements from an

       *  %unordered_multimap.

       *  @param  __first  Iterator pointing to the start of the range to be

       *                  erased.

       *  @param __last  Iterator pointing to the end of the range to

       *                be erased.

       *  @return The iterator @a __last.

       *

       *  This function erases a sequence of elements from an

       *  %unordered_multimap.

       *  Note that this function only erases the elements, and that if

       *  the element is itself a pointer, the pointed-to memory is not touched

       *  in any way.  Managing the pointer is the user's responsibility.

       */

      iterator

      erase(const_iterator __first, const_iterator __last)

      { return _M_h.erase(__first, __last); }

      /**

       *  Erases all elements in an %unordered_multimap.

       *  Note that this function only erases the elements, and that if the

       *  elements themselves are pointers, the pointed-to memory is not touched

       *  in any way.  Managing the pointer is the user's responsibility.

       */

      void

      clear() noexcept

      { _M_h.clear(); }

      /**

       *  @brief  Swaps data with another %unordered_multimap.

       *  @param  __x  An %unordered_multimap of the same element and allocator

       *  types.

       *

       *  This exchanges the elements between two %unordered_multimap in

       *  constant time.

       *  Note that the global std::swap() function is specialized such that

       *  std::swap(m1,m2) will feed to this function.

       */

      void

      swap(unordered_multimap& __x)

      noexcept( noexcept(_M_h.swap(__x._M_h)) )

      { _M_h.swap(__x._M_h); }

      // observers.

      ///  Returns the hash functor object with which the %unordered_multimap

      ///  was constructed.

      hasher

      hash_function() const

      { return _M_h.hash_function(); }

      ///  Returns the key comparison object with which the %unordered_multimap

      ///  was constructed.

      key_equal

      key_eq() const

      { return _M_h.key_eq(); }