///\file

/******************************************************************************
The MIT License(MIT)

Embedded Template Library.
https://github.com/ETLCPP/etl
https://www.etlcpp.com

Copyright(c) 2017 John Wellbelove

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files(the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and / or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions :

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
******************************************************************************/

#ifndef ETL_REFERENCE_FLAT_MULTIMAP_INCLUDED
#define ETL_REFERENCE_FLAT_MULTIMAP_INCLUDED

#include "platform.h"
#include "exception.h"
#include "error_handler.h"
#include "debug_count.h"
#include "vector.h"
#include "iterator.h"
#include "nth_type.h"
#include "type_traits.h"
#include "type_traits.h"

#include "private/comparator_is_transparent.h"

#include <stddef.h>

namespace etl
{
  //***************************************************************************
  ///\ingroup reference_flat_multimap
  /// Exception base for reference_flat_multimaps
  //***************************************************************************
  class flat_multimap_exception : public exception
  {
  public:

    flat_multimap_exception(string_type reason_, string_type file_name_, numeric_type line_number_)
      : exception(reason_, file_name_, line_number_)
    {
    }
  };

  //***************************************************************************
  ///\ingroup reference_flat_multimap
  /// Vector full exception.
  //***************************************************************************
  class flat_multimap_full : public flat_multimap_exception
  {
  public:

    flat_multimap_full(string_type file_name_, numeric_type line_number_)
      : flat_multimap_exception(ETL_ERROR_TEXT("flat_multimap:full", ETL_REFERENCE_FLAT_MULTIMAP_FILE_ID"A"), file_name_, line_number_)
    {
    }
  };

  //***************************************************************************
  /// The base class for specifically sized reference_flat_multimaps.
  /// Can be used as a reference type for all reference_flat_multimaps containing a specific type.
  ///\ingroup reference_flat_multimap
  //***************************************************************************
  template <typename TKey, typename TMapped, typename TKeyCompare = etl::less<TKey> >
  class ireference_flat_multimap
  {
  public:

    typedef ETL_OR_STD::pair<const TKey, TMapped> value_type;

  protected:

    typedef etl::ivector<value_type*> lookup_t;

  public:

    typedef TKey              key_type;
    typedef TMapped           mapped_type;
    typedef TKeyCompare       key_compare;
    typedef value_type&       reference;
    typedef const value_type& const_reference;
    typedef value_type*       pointer;
    typedef const value_type* const_pointer;
    typedef size_t            size_type;

    //*************************************************************************
    class iterator : public etl::iterator<ETL_OR_STD::bidirectional_iterator_tag, value_type>
    {
    public:

      friend class ireference_flat_multimap;
      friend class const_iterator;

      iterator()
      {
      }

      iterator(typename lookup_t::iterator ilookup_)
        : ilookup(ilookup_)
      {
      }

      iterator(const iterator& other)
        : ilookup(other.ilookup)
      {
      }

      iterator& operator =(const iterator& other)
      {
        ilookup = other.ilookup;
        return *this;
      }

      iterator& operator ++()
      {
        ++ilookup;
        return *this;
      }

      iterator operator ++(int)
      {
        iterator temp(*this);
        ++ilookup;
        return temp;
      }

      iterator& operator --()
      {
        --ilookup;
        return *this;
      }

      iterator operator --(int)
      {
        iterator temp(*this);
        --ilookup;
        return temp;
      }

      reference operator *() const
      {
        return *(*ilookup);
      }

      pointer operator &() const
      {
        return etl::addressof(*(*ilookup));
      }

      pointer operator ->() const
      {
        return etl::addressof(*(*ilookup));
      }

      friend bool operator == (const iterator& lhs, const iterator& rhs)
      {
        return lhs.ilookup == rhs.ilookup;
      }

      friend bool operator != (const iterator& lhs, const iterator& rhs)
      {
        return !(lhs == rhs);
      }

    private:

      typename lookup_t::iterator ilookup;
    };

    //*************************************************************************
    class const_iterator : public etl::iterator<ETL_OR_STD::bidirectional_iterator_tag, const value_type>
    {
    public:

      friend class ireference_flat_multimap;

      const_iterator()
      {
      }

      const_iterator(typename lookup_t::const_iterator ilookup_)
        : ilookup(ilookup_)
      {
      }

      const_iterator(const typename ireference_flat_multimap::iterator& other)
        : ilookup(other.ilookup)
      {
      }

      const_iterator(const const_iterator& other)
        : ilookup(other.ilookup)
      {
      }

      const_iterator& operator =(const iterator& other)
      {
        ilookup = other.ilookup;
        return *this;
      }

      const_iterator& operator =(const const_iterator& other)
      {
        ilookup = other.ilookup;
        return *this;
      }

      const_iterator& operator ++()
      {
        ++ilookup;
        return *this;
      }

      const_iterator operator ++(int)
      {
        const_iterator temp(*this);
        ++ilookup;
        return temp;
      }

      const_iterator& operator --()
      {
        --ilookup;
        return *this;
      }

      const_iterator operator --(int)
      {
        const_iterator temp(*this);
        --ilookup;
        return temp;
      }

      const_reference operator *() const
      {
        return *(*ilookup);
      }

      const_pointer operator &() const
      {
        return etl::addressof(*(*ilookup));
      }

      const_pointer operator ->() const
      {
        return etl::addressof(*(*ilookup));
      }

      friend bool operator == (const const_iterator& lhs, const const_iterator& rhs)
      {
        return lhs.ilookup == rhs.ilookup;
      }

      friend bool operator != (const const_iterator& lhs, const const_iterator& rhs)
      {
        return !(lhs == rhs);
      }

    private:

      typename lookup_t::const_iterator ilookup;
    };

    typedef ETL_OR_STD::reverse_iterator<iterator>       reverse_iterator;
    typedef ETL_OR_STD::reverse_iterator<const_iterator> const_reverse_iterator;
    typedef typename etl::iterator_traits<iterator>::difference_type difference_type;

  protected:

    typedef const TKey& key_parameter_t;

  private:

    //*********************************************************************
    /// How to compare elements and keys.
    //*********************************************************************
    class Compare
    {
    public:

      bool operator ()(const value_type& element, key_type key) const
      {
        return comp(element.first, key);
      }

      bool operator ()(key_type key, const value_type& element) const
      {
        return comp(key, element.first);
      }

#if ETL_USING_CPP11
      template <typename K, typename KC = TKeyCompare, etl::enable_if_t<comparator_is_transparent<KC>::value, int> = 0>
      bool operator ()(const value_type& element, const K& key) const
      {
        return comp(element.first, key);
      }

      template <typename K, typename KC = TKeyCompare, etl::enable_if_t<comparator_is_transparent<KC>::value, int> = 0>
      bool operator ()(const K& key, const value_type& element) const
      {
        return comp(key, element.first);
      }
#endif

      key_compare comp;
    };

  public:

    //*********************************************************************
    /// Returns an iterator to the beginning of the reference_flat_multimap.
    ///\return An iterator to the beginning of the reference_flat_multimap.
    //*********************************************************************
    iterator begin()
    {
      return iterator(lookup.begin());
    }

    //*********************************************************************
    /// Returns a const_iterator to the beginning of the reference_flat_multimap.
    ///\return A const iterator to the beginning of the reference_flat_multimap.
    //*********************************************************************
    const_iterator begin() const
    {
      return const_iterator(lookup.begin());
    }

    //*********************************************************************
    /// Returns an iterator to the end of the reference_flat_multimap.
    ///\return An iterator to the end of the reference_flat_multimap.
    //*********************************************************************
    iterator end()
    {
      return iterator(lookup.end());
    }

    //*********************************************************************
    /// Returns a const_iterator to the end of the reference_flat_multimap.
    ///\return A const iterator to the end of the reference_flat_multimap.
    //*********************************************************************
    const_iterator end() const
    {
      return const_iterator(lookup.end());
    }

    //*********************************************************************
    /// Returns a const_iterator to the beginning of the reference_flat_multimap.
    ///\return A const iterator to the beginning of the reference_flat_multimap.
    //*********************************************************************
    const_iterator cbegin() const
    {
      return const_iterator(lookup.cbegin());
    }

    //*********************************************************************
    /// Returns a const_iterator to the end of the reference_flat_multimap.
    ///\return A const iterator to the end of the reference_flat_multimap.
    //*********************************************************************
    const_iterator cend() const
    {
      return const_iterator(lookup.cend());
    }

    //*********************************************************************
    /// Returns an reverse iterator to the reverse beginning of the reference_flat_multimap.
    ///\return Iterator to the reverse beginning of the reference_flat_multimap.
    //*********************************************************************
    reverse_iterator rbegin()
    {
      return reverse_iterator(lookup.rbegin());
    }

    //*********************************************************************
    /// Returns a const reverse iterator to the reverse beginning of the reference_flat_multimap.
    ///\return Const iterator to the reverse beginning of the reference_flat_multimap.
    //*********************************************************************
    const_reverse_iterator rbegin() const
    {
      return const_reverse_iterator(lookup.rbegin());
    }

    //*********************************************************************
    /// Returns a reverse iterator to the end + 1 of the reference_flat_multimap.
    ///\return Reverse iterator to the end + 1 of the reference_flat_multimap.
    //*********************************************************************
    reverse_iterator rend()
    {
      return reverse_iterator(lookup.rend());
    }

    //*********************************************************************
    /// Returns a const reverse iterator to the end + 1 of the reference_flat_multimap.
    ///\return Const reverse iterator to the end + 1 of the reference_flat_multimap.
    //*********************************************************************
    const_reverse_iterator rend() const
    {
      return const_reverse_iterator(lookup.rend());
    }

    //*********************************************************************
    /// Returns a const reverse iterator to the reverse beginning of the reference_flat_multimap.
    ///\return Const reverse iterator to the reverse beginning of the reference_flat_multimap.
    //*********************************************************************
    const_reverse_iterator crbegin() const
    {
      return const_reverse_iterator(lookup.crbegin());
    }

    //*********************************************************************
    /// Returns a const reverse iterator to the end + 1 of the reference_flat_multimap.
    ///\return Const reverse iterator to the end + 1 of the reference_flat_multimap.
    //*********************************************************************
    const_reverse_iterator crend() const
    {
      return const_reverse_iterator(lookup.crend());
    }

    //*********************************************************************
    /// Assigns values to the reference_flat_multimap.
    /// If asserts or exceptions are enabled, emits reference_flat_multimap_full if the reference_flat_multimap does not have enough free space.
    /// If asserts or exceptions are enabled, emits reference_flat_multimap_iterator if the iterators are reversed.
    ///\param first The iterator to the first element.
    ///\param last  The iterator to the last element + 1.
    //*********************************************************************
    template <typename TIterator>
    void assign(TIterator first, TIterator last)
    {
#if ETL_IS_DEBUG_BUILD
      difference_type d = etl::distance(first, last);
      ETL_ASSERT(d <= difference_type(capacity()), ETL_ERROR(flat_multimap_full));
#endif

      clear();

      while (first != last)
      {
        insert(*first);
        ++first;
      }
    }

    //*********************************************************************
    /// Inserts a value to the reference_flat_multimap.
    /// If asserts or exceptions are enabled, emits reference_flat_multimap_full if the reference_flat_multimap is already full.
    ///\param value    The value to insert.
    //*********************************************************************
    ETL_OR_STD::pair<iterator, bool> insert(value_type& value)
    {
      ETL_ASSERT(!lookup.full(), ETL_ERROR(flat_multimap_full));

      ETL_OR_STD::pair<iterator, bool> result(end(), false);

      iterator i_element = upper_bound(value.first);

      return insert_at(i_element, value);
    }

    //*********************************************************************
    /// Inserts a value to the flat_multi.
    /// If asserts or exceptions are enabled, emits flat_map_full if the flat_map is already full.
    ///\param position The position to insert at.
    ///\param value    The value to insert.
    //*********************************************************************
    iterator insert(const_iterator /*position*/, const value_type& value)
    {
      return insert(value).first;
    }

    //*********************************************************************
    /// Inserts a range of values to the reference_flat_multimap.
    /// If asserts or exceptions are enabled, emits reference_flat_multimap_full if the reference_flat_multimap does not have enough free space.
    ///\param position The position to insert at.
    ///\param first    The first element to add.
    ///\param last     The last + 1 element to add.
    //*********************************************************************
    template <class TIterator>
    void insert(TIterator first, TIterator last)
    {
      while (first != last)
      {
        insert(*first);
        ++first;
      }
    }

    //*********************************************************************
    /// Erases an element.
    ///\param key The key to erase.
    ///\return The number of elements erased. 0 or 1.
    //*********************************************************************
    size_t erase(key_parameter_t key)
    {
      ETL_OR_STD::pair<iterator, iterator> range = equal_range(key);

      if (range.first == end())
      {
        return 0;
      }
      else
      {
        size_t d = etl::distance(range.first, range.second);
        erase(range.first, range.second);
        return d;
      }
    }

#if ETL_USING_CPP11
    //*********************************************************************
    template <typename K, typename KC = TKeyCompare, etl::enable_if_t<comparator_is_transparent<KC>::value, int> = 0>
    size_t erase(K&& key)
    {
      ETL_OR_STD::pair<iterator, iterator> range = equal_range(key);

      if (range.first == end())
      {
        return 0U;
      }
      else
      {
        size_t d = etl::distance(range.first, range.second);
        erase(range.first, range.second);
        return d;
      }
    }
#endif

    //*********************************************************************
    /// Erases an element.
    ///\param i_element Iterator to the element.
    //*********************************************************************
    iterator erase(iterator i_element)
    {
      return lookup.erase(i_element.ilookup);
    }

    //*********************************************************************
    /// Erases an element.
    ///\param i_element Iterator to the element.
    //*********************************************************************
    iterator erase(const_iterator i_element)
    {
      return lookup.erase(i_element.ilookup);
    }

    //*********************************************************************
    /// Erases a range of elements.
    /// The range includes all the elements between first and last, including the
    /// element pointed by first, but not the one pointed by last.
    ///\param first Iterator to the first element.
    ///\param last  Iterator to the last element.
    //*********************************************************************
    iterator erase(const_iterator first, const_iterator last)
    {
      return lookup.erase(first.ilookup, last.ilookup);
    }

    //*************************************************************************
    /// Clears the reference_flat_multimap.
    //*************************************************************************
    void clear()
    {
      lookup.clear();
    }

    //*********************************************************************
    /// Finds an element.
    ///\param key The key to search for.
    ///\return An iterator pointing to the element or end() if not found.
    //*********************************************************************
    iterator find(key_parameter_t key)
    {
      iterator itr = lower_bound(key);

      if (itr != end())
      {
        if (!key_compare()(itr->first, key) && !key_compare()(key, itr->first))
        {
          return itr;
        }
        else
        {
          return end();
        }
      }

      return end();
    }

#if ETL_USING_CPP11
    //*********************************************************************
    template <typename K, typename KC = TKeyCompare, etl::enable_if_t<comparator_is_transparent<KC>::value, int> = 0>
    iterator find(const K& key)
    {
      iterator itr = lower_bound(key);

      if (itr != end())
      {
        if (!key_compare()(itr->first, key) && !key_compare()(key, itr->first))
        {
          return itr;
        }
        else
        {
          return end();
        }
      }

      return end();
    }
#endif

    //*********************************************************************
    /// Finds an element.
    ///\param key The key to search for.
    ///\return An iterator pointing to the element or end() if not found.
    //*********************************************************************
    const_iterator find(key_parameter_t key) const
    {
      const_iterator itr = lower_bound(key);

      if (itr != end())
      {
        if (!key_compare()(itr->first, key) && !key_compare()(key, itr->first))
        {
          return itr;
        }
        else
        {
          return end();
        }
      }

      return end();
    }

#if ETL_USING_CPP11
    //*********************************************************************
    template <typename K, typename KC = TKeyCompare, etl::enable_if_t<comparator_is_transparent<KC>::value, int> = 0>
    const_iterator find(const K& key) const
    {
      const_iterator itr = lower_bound(key);

      if (itr != end())
      {
        if (!key_compare()(itr->first, key) && !key_compare()(key, itr->first))
        {
          return itr;
        }
        else
        {
          return end();
        }
      }

      return end();
    }
#endif

    //*********************************************************************
    /// Counts an element.
    ///\param key The key to search for.
    ///\return 1 if the key exists, otherwise 0.
    //*********************************************************************
    size_t count(key_parameter_t key) const
    {
      ETL_OR_STD::pair<const_iterator, const_iterator> range = equal_range(key);

      return etl::distance(range.first, range.second);
    }

#if ETL_USING_CPP11
    //*********************************************************************
    template <typename K, typename KC = TKeyCompare, etl::enable_if_t<comparator_is_transparent<KC>::value, int> = 0>
    size_t count(const K& key) const
    {
      ETL_OR_STD::pair<const_iterator, const_iterator> range = equal_range(key);

      return etl::distance(range.first, range.second);
    }
#endif

    //*********************************************************************
    /// Finds the lower bound of a key
    ///\param key The key to search for.
    ///\return An iterator.
    //*********************************************************************
    iterator lower_bound(key_parameter_t key)
    {
      return etl::lower_bound(begin(), end(), key, compare);
    }

#if ETL_USING_CPP11
    //*********************************************************************
    template <typename K, typename KC = TKeyCompare, etl::enable_if_t<comparator_is_transparent<KC>::value, int> = 0>
    iterator lower_bound(const K& key)
    {
      return etl::lower_bound(begin(), end(), key, compare);
    }
#endif

    //*********************************************************************
    /// Finds the lower bound of a key
    ///\param key The key to search for.
    ///\return An iterator.
    //*********************************************************************
    const_iterator lower_bound(key_parameter_t key) const
    {
      return etl::lower_bound(cbegin(), cend(), key, compare);
    }

#if ETL_USING_CPP11
    //*********************************************************************
    template <typename K, typename KC = TKeyCompare, etl::enable_if_t<comparator_is_transparent<KC>::value, int> = 0>
    const_iterator lower_bound(const K& key) const
    {
      return etl::lower_bound(cbegin(), cend(), key, compare);
    }
#endif

    //*********************************************************************
    /// Finds the upper bound of a key
    ///\param key The key to search for.
    ///\return An iterator.
    //*********************************************************************
    iterator upper_bound(key_parameter_t key)
    {
      return etl::upper_bound(begin(), end(), key, compare);
    }

#if ETL_USING_CPP11
    //*********************************************************************
    template <typename K, typename KC = TKeyCompare, etl::enable_if_t<comparator_is_transparent<KC>::value, int> = 0>
    iterator upper_bound(const K& key)
    {
      return etl::upper_bound(begin(), end(), key, compare);
    }
#endif

    //*********************************************************************
    /// Finds the upper bound of a key
    ///\param key The key to search for.
    ///\return An iterator.
    //*********************************************************************
    const_iterator upper_bound(key_parameter_t key) const
    {
      return etl::upper_bound(begin(), end(), key, compare);
    }

#if ETL_USING_CPP11
    //*********************************************************************
    template <typename K, typename KC = TKeyCompare, etl::enable_if_t<comparator_is_transparent<KC>::value, int> = 0>
    const_iterator upper_bound(const K& key) const
    {
      return etl::upper_bound(begin(), end(), key, compare);
    }
#endif

    //*********************************************************************
    /// Finds the range of equal elements of a key
    ///\param key The key to search for.
    ///\return An iterator pair.
    //*********************************************************************
    ETL_OR_STD::pair<iterator, iterator> equal_range(key_parameter_t key)
    {
      iterator i_lower = etl::lower_bound(begin(), end(), key, compare);

      return ETL_OR_STD::make_pair(i_lower, etl::upper_bound(i_lower, end(), key, compare));
    }

#if ETL_USING_CPP11
    //*********************************************************************
    template <typename K, typename KC = TKeyCompare, etl::enable_if_t<comparator_is_transparent<KC>::value, int> = 0>
    ETL_OR_STD::pair<iterator, iterator> equal_range(const K& key)
    {
      iterator i_lower = etl::lower_bound(begin(), end(), key, compare);

      return ETL_OR_STD::make_pair(i_lower, etl::upper_bound(i_lower, end(), key, compare));
    }
#endif

    //*********************************************************************
    /// Finds the range of equal elements of a key
    ///\param key The key to search for.
    ///\return An iterator pair.
    //*********************************************************************
    ETL_OR_STD::pair<const_iterator, const_iterator> equal_range(key_parameter_t key) const
    {
      const_iterator i_lower = etl::lower_bound(cbegin(), cend(), key, compare);

      return ETL_OR_STD::make_pair(i_lower, etl::upper_bound(i_lower, cend(), key, compare));
    }

#if ETL_USING_CPP11
    //*********************************************************************
    template <typename K, typename KC = TKeyCompare, etl::enable_if_t<comparator_is_transparent<KC>::value, int> = 0>
    ETL_OR_STD::pair<const_iterator, const_iterator> equal_range(const K& key) const
    {
      const_iterator i_lower = etl::lower_bound(cbegin(), cend(), key, compare);

      return ETL_OR_STD::make_pair(i_lower, etl::upper_bound(i_lower, cend(), key, compare));
    }
#endif

    //*************************************************************************
    /// Check if the map contains the key.
    //*************************************************************************
    bool contains(const TKey& key) const
    {
      return find(key) != end();
    }

#if ETL_USING_CPP11
    //*************************************************************************
    template <typename K, typename KC = TKeyCompare, etl::enable_if_t<comparator_is_transparent<KC>::value, int> = 0>
    bool contains(const K& k) const
    {
      return find(k) != end();
    }
#endif

    //*************************************************************************
    /// Gets the current size of the flat_multiset.
    ///\return The current size of the flat_multiset.
    //*************************************************************************
    size_type size() const
    {
      return lookup.size();
    }

    //*************************************************************************
    /// Checks the 'empty' state of the flat_multiset.
    ///\return <b>true</b> if empty.
    //*************************************************************************
    bool empty() const
    {
      return lookup.empty();
    }

    //*************************************************************************
    /// Checks the 'full' state of the flat_multiset.
    ///\return <b>true</b> if full.
    //*************************************************************************
    bool full() const
    {
      return lookup.full();
    }

    //*************************************************************************
    /// Returns the capacity of the flat_multiset.
    ///\return The capacity of the flat_multiset.
    //*************************************************************************
    size_type capacity() const
    {
      return lookup.capacity();
    }

    //*************************************************************************
    /// Returns the maximum possible size of the flat_multiset.
    ///\return The maximum size of the flat_multiset.
    //*************************************************************************
    size_type max_size() const
    {
      return lookup.max_size();
    }

    //*************************************************************************
    /// Returns the remaining capacity.
    ///\return The remaining capacity.
    //*************************************************************************
    size_t available() const
    {
      return lookup.available();
    }

  protected:

    //*********************************************************************
    /// Constructor.
    //*********************************************************************
    ireference_flat_multimap(lookup_t& lookup_)
      : lookup(lookup_)
    {
    }

    //*********************************************************************
    /// Inserts a value to the reference_flat_multimap.
    ///\param i_element The place to insert.
    ///\param value     The value to insert.
    //*********************************************************************
    ETL_OR_STD::pair<iterator, bool> insert_at(iterator i_element, value_type& value)
    {
      ETL_OR_STD::pair<iterator, bool> result(end(), false);

      if (i_element == end())
      {
        // At the end.
        lookup.push_back(&value);
        result.first = --end();
        result.second = true;
      }
      else
      {
        // Not at the end.
        lookup.insert(i_element.ilookup, &value);
        result.first = i_element;
        result.second = true;
      }

      return result;
    }

  private:

    // Disable copy construction and assignment.
    ireference_flat_multimap(const ireference_flat_multimap&);
    ireference_flat_multimap& operator = (const ireference_flat_multimap&);

    lookup_t&  lookup;

    Compare compare;

    //*************************************************************************
    /// Destructor.
    //*************************************************************************
#if defined(ETL_POLYMORPHIC_REFERENCE_FLAT_MULTIMAP) || defined(ETL_POLYMORPHIC_CONTAINERS)
  public:
    virtual ~ireference_flat_multimap()
    {
    }
#else
  protected:
    ~ireference_flat_multimap()
    {
    }
#endif
  };

  //***************************************************************************
  /// Equal operator.
  ///\param lhs Reference to the first reference_flat_multimap.
  ///\param rhs Reference to the second reference_flat_multimap.
  ///\return <b>true</b> if the arrays are equal, otherwise <b>false</b>
  ///\ingroup reference_flat_multimap
  //***************************************************************************
  template <typename TKey, typename TMapped, typename TKeyCompare>
  bool operator ==(const etl::ireference_flat_multimap<TKey, TMapped, TKeyCompare>& lhs, const etl::ireference_flat_multimap<TKey, TMapped, TKeyCompare>& rhs)
  {
    return (lhs.size() == rhs.size()) && etl::equal(lhs.begin(), lhs.end(), rhs.begin());
  }

  //***************************************************************************
  /// Not equal operator.
  ///\param lhs Reference to the first reference_flat_multimap.
  ///\param rhs Reference to the second reference_flat_multimap.
  ///\return <b>true</b> if the arrays are not equal, otherwise <b>false</b>
  ///\ingroup reference_flat_multimap
  //***************************************************************************
  template <typename TKey, typename TMapped, typename TKeyCompare>
  bool operator !=(const etl::ireference_flat_multimap<TKey, TMapped, TKeyCompare>& lhs, const etl::ireference_flat_multimap<TKey, TMapped, TKeyCompare>& rhs)
  {
    return !(lhs == rhs);
  }

  //***************************************************************************
  /// A reference_flat_multimap implementation that uses a fixed size buffer.
  ///\tparam TKey     The key type.
  ///\tparam TValue   The value type.
  ///\tparam TCompare The type to compare keys. Default = etl::less<TKey>
  ///\tparam MAX_SIZE_ The maximum number of elements that can be stored.
  ///\ingroup reference_flat_multimap
  //***************************************************************************
  template <typename TKey, typename TValue, const size_t MAX_SIZE_, typename TCompare = etl::less<TKey> >
  class reference_flat_multimap : public ireference_flat_multimap<TKey, TValue, TCompare>
  {
  public:

    static ETL_CONSTANT size_t MAX_SIZE = MAX_SIZE_;

    //*************************************************************************
    /// Constructor.
    //*************************************************************************
    reference_flat_multimap()
      : ireference_flat_multimap<TKey, TValue, TCompare>(lookup)
    {
    }

    //*************************************************************************
    /// Copy constructor.
    //*************************************************************************
    reference_flat_multimap(const reference_flat_multimap& other)
      : ireference_flat_multimap<TKey, TValue, TCompare>(lookup)
    {
      ireference_flat_multimap<TKey, TValue, TCompare>::assign(other.cbegin(), other.cend());
    }

    //*************************************************************************
    /// Constructor, from an iterator range.
    ///\tparam TIterator The iterator type.
    ///\param first The iterator to the first element.
    ///\param last  The iterator to the last element + 1.
    //*************************************************************************
    template <typename TIterator>
    reference_flat_multimap(TIterator first, TIterator last)
      : ireference_flat_multimap<TKey, TValue, TCompare>(lookup)
    {
      ireference_flat_multimap<TKey, TValue, TCompare>::assign(first, last);
    }

    //*************************************************************************
    /// Destructor.
    //*************************************************************************
    ~reference_flat_multimap()
    {
      ireference_flat_multimap<TKey, TValue, TCompare>::clear();
    }

  private:

    typedef typename ireference_flat_multimap<TKey, TValue, TCompare>::value_type node_t;

    // The vector that stores pointers to the nodes.
    etl::vector<node_t*, MAX_SIZE> lookup;
  };

  template <typename TKey, typename TValue, const size_t MAX_SIZE_, typename TCompare>
  ETL_CONSTANT size_t reference_flat_multimap< TKey, TValue, MAX_SIZE_, TCompare>::MAX_SIZE;

  //*************************************************************************
  /// Template deduction guides.
  //*************************************************************************
#if ETL_USING_CPP17 && ETL_HAS_INITIALIZER_LIST
  template <typename... TPairs>
  reference_flat_multimap(TPairs...) -> reference_flat_multimap<typename etl::nth_type_t<0, TPairs...>::first_type,
                                                                typename etl::nth_type_t<0, TPairs...>::second_type,
                                                                sizeof...(TPairs)>;
#endif

  //*************************************************************************
  /// Make
  //*************************************************************************
#if ETL_USING_CPP11 && ETL_HAS_INITIALIZER_LIST
  template <typename TKey, typename TMapped, typename TKeyCompare = etl::less<TKey>, typename... TPairs>
  constexpr auto make_reference_flat_multimap(TPairs&&... pairs) -> etl::reference_flat_multimap<TKey, TMapped, sizeof...(TPairs), TKeyCompare>
  {
    return { etl::forward<TPairs>(pairs)... };
  }
#endif
}

#endif