hopscotch_map.h

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/**
 * MIT License
 *
 * Copyright (c) 2017 Tessil
 *
 * 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 TSL_HOPSCOTCH_MAP_H
#define TSL_HOPSCOTCH_MAP_H
 
#include "hopscotch_hash.h"
#include <algorithm>
#include <cstddef>
#include <functional>
#include <initializer_list>
#include <list>
#include <memory>
#include <type_traits>
#include <utility>
 
namespace tsl {
 
  /**
   * Implementation of a hash map using the hopscotch hashing algorithm.
   *
   * The Key and the value T must be either nothrow move-constructible, copy-constuctible or both.
   *
   * The size of the neighborhood (NeighborhoodSize) must be > 0 and <= 62 if StoreHash is false.
   * When StoreHash is true, 32-bits of the hash will be stored alongside the neighborhood limiting
   * the NeighborhoodSize to <= 30. There is no memory usage difference between
   * 'NeighborhoodSize 62; StoreHash false' and 'NeighborhoodSize 30; StoreHash true'.
   *
   * Storing the hash may improve performance on insert during the rehash process if the hash takes
   * time to compute. It may also improve read performance if the KeyEqual function takes time (or
   * incurs a cache-miss). If used with simple Hash and KeyEqual it may slow things down.
   *
   * StoreHash can only be set if the GrowthPolicy is set to tsl::power_of_two_growth_policy.
   *
   * GrowthPolicy defines how the map grows and consequently how a hash value is mapped to a bucket.
   * By default the map uses tsl::power_of_two_growth_policy. This policy keeps the number of
   * buckets to a power of two and uses a mask to map the hash to a bucket instead of the slow
   * modulo. You may define your own growth policy, check tsl::power_of_two_growth_policy for the
   * interface.
   *
   * If the destructors of Key or T throw an exception, behaviour of the class is undefined.
   *
   * Iterators invalidation:
   *  - clear, operator=, reserve, rehash: always invalidate the iterators.
   *  - insert, emplace, emplace_hint, operator[]: if there is an effective insert, invalidate the
   * iterators if a displacement is needed to resolve a collision (which mean that most of the time,
   *    insert will invalidate the iterators). Or if there is a rehash.
   *  - erase: iterator on the erased element is the only one which become invalid.
   */
  template <class Key, class T, class Hash = std::hash<Key>, class KeyEqual = std::equal_to<Key>,
            class Allocator = std::allocator<std::pair<Key, T>>, unsigned int NeighborhoodSize = 62,
            bool StoreHash = false, class GrowthPolicy = tsl::hh::power_of_two_growth_policy<2>>
  class hopscotch_map
  {
  private:
    template <typename U>
    using has_is_transparent = tsl::detail_hopscotch_hash::has_is_transparent<U>;
 
    class KeySelect
    {
    public:
      using key_type = Key;
 
      const key_type &operator()(const std::pair<Key, T> &key_value) const
      {
        return key_value.first;
      }
 
      key_type &operator()(std::pair<Key, T> &key_value) { return key_value.first; }
    };
 
    class ValueSelect
    {
    public:
      using value_type = T;
 
      const value_type &operator()(const std::pair<Key, T> &key_value) const
      {
        return key_value.second;
      }
 
      value_type &operator()(std::pair<Key, T> &key_value) { return key_value.second; }
    };
 
    using overflow_container_type = std::list<std::pair<Key, T>, Allocator>;
    using ht =
        detail_hopscotch_hash::hopscotch_hash<std::pair<Key, T>, KeySelect, ValueSelect, Hash,
                                              KeyEqual, Allocator, NeighborhoodSize, StoreHash,
                                              GrowthPolicy, overflow_container_type>;
 
  public:
    using key_type        = typename ht::key_type;
    using mapped_type     = T;
    using value_type      = typename ht::value_type;
    using size_type       = typename ht::size_type;
    using difference_type = typename ht::difference_type;
    using hasher          = typename ht::hasher;
    using key_equal       = typename ht::key_equal;
    using allocator_type  = typename ht::allocator_type;
    using reference       = typename ht::reference;
    using const_reference = typename ht::const_reference;
    using pointer         = typename ht::pointer;
    using const_pointer   = typename ht::const_pointer;
    using iterator        = typename ht::iterator;
    using const_iterator  = typename ht::const_iterator;
 
    /*
     * Constructors
     */
    hopscotch_map() : hopscotch_map(ht::DEFAULT_INIT_BUCKETS_SIZE) {}
 
    explicit hopscotch_map(size_type bucket_count, const Hash &hash = Hash(),
                           const KeyEqual &equal = KeyEqual(), const Allocator &alloc = Allocator())
        : m_ht(bucket_count, hash, equal, alloc, ht::DEFAULT_MAX_LOAD_FACTOR)
    {
    }
 
    hopscotch_map(size_type bucket_count, const Allocator &alloc)
        : hopscotch_map(bucket_count, Hash(), KeyEqual(), alloc)
    {
    }
 
    hopscotch_map(size_type bucket_count, const Hash &hash, const Allocator &alloc)
        : hopscotch_map(bucket_count, hash, KeyEqual(), alloc)
    {
    }
 
    explicit hopscotch_map(const Allocator &alloc)
        : hopscotch_map(ht::DEFAULT_INIT_BUCKETS_SIZE, alloc)
    {
    }
 
    template <class InputIt>
    hopscotch_map(InputIt first, InputIt last,
                  size_type bucket_count = ht::DEFAULT_INIT_BUCKETS_SIZE, const Hash &hash = Hash(),
                  const KeyEqual &equal = KeyEqual(), const Allocator &alloc = Allocator())
        : hopscotch_map(bucket_count, hash, equal, alloc)
    {
      insert(first, last);
    }
 
    template <class InputIt>
    hopscotch_map(InputIt first, InputIt last, size_type bucket_count, const Allocator &alloc)
        : hopscotch_map(first, last, bucket_count, Hash(), KeyEqual(), alloc)
    {
    }
 
    template <class InputIt>
    hopscotch_map(InputIt first, InputIt last, size_type bucket_count, const Hash &hash,
                  const Allocator &alloc)
        : hopscotch_map(first, last, bucket_count, hash, KeyEqual(), alloc)
    {
    }
 
    hopscotch_map(std::initializer_list<value_type> init,
                  size_type bucket_count = ht::DEFAULT_INIT_BUCKETS_SIZE, const Hash &hash = Hash(),
                  const KeyEqual &equal = KeyEqual(), const Allocator &alloc = Allocator())
        : hopscotch_map(init.begin(), init.end(), bucket_count, hash, equal, alloc)
    {
    }
 
    hopscotch_map(std::initializer_list<value_type> init, size_type bucket_count,
                  const Allocator &alloc)
        : hopscotch_map(init.begin(), init.end(), bucket_count, Hash(), KeyEqual(), alloc)
    {
    }
 
    hopscotch_map(std::initializer_list<value_type> init, size_type bucket_count, const Hash &hash,
                  const Allocator &alloc)
        : hopscotch_map(init.begin(), init.end(), bucket_count, hash, KeyEqual(), alloc)
    {
    }
 
    hopscotch_map &operator=(std::initializer_list<value_type> ilist)
    {
      m_ht.clear();
 
      m_ht.reserve(ilist.size());
      m_ht.insert(ilist.begin(), ilist.end());
 
      return *this;
    }
 
    allocator_type get_allocator() const { return m_ht.get_allocator(); }
 
    /*
     * Iterators
     */
    iterator       begin() noexcept { return m_ht.begin(); }
    const_iterator begin() const noexcept { return m_ht.begin(); }
    const_iterator cbegin() const noexcept { return m_ht.cbegin(); }
 
    iterator       end() noexcept { return m_ht.end(); }
    const_iterator end() const noexcept { return m_ht.end(); }
    const_iterator cend() const noexcept { return m_ht.cend(); }
 
    /*
     * Capacity
     */
    bool      empty() const noexcept { return m_ht.empty(); }
    size_type size() const noexcept { return m_ht.size(); }
    size_type max_size() const noexcept { return m_ht.max_size(); }
 
    /*
     * Modifiers
     */
    void clear() noexcept { m_ht.clear(); }
 
    std::pair<iterator, bool> insert(const value_type &value) { return m_ht.insert(value); }
 
    template <class P, typename std::enable_if<std::is_constructible<value_type, P &&>::value>::type
                           * = nullptr>
    std::pair<iterator, bool> insert(P &&value)
    {
      return m_ht.insert(std::forward<P>(value));
    }
 
    std::pair<iterator, bool> insert(value_type &&value) { return m_ht.insert(std::move(value)); }
 
    iterator insert(const_iterator hint, const value_type &value)
    {
      return m_ht.insert(hint, value);
    }
 
    template <class P, typename std::enable_if<std::is_constructible<value_type, P &&>::value>::type
                           * = nullptr>
    iterator insert(const_iterator hint, P &&value)
    {
      return m_ht.insert(hint, std::forward<P>(value));
    }
 
    iterator insert(const_iterator hint, value_type &&value)
    {
      return m_ht.insert(hint, std::move(value));
    }
 
    template <class InputIt> void insert(InputIt first, InputIt last) { m_ht.insert(first, last); }
 
    void insert(std::initializer_list<value_type> ilist)
    {
      m_ht.insert(ilist.begin(), ilist.end());
    }
 
    template <class M> std::pair<iterator, bool> insert_or_assign(const key_type &k, M &&obj)
    {
      return m_ht.insert_or_assign(k, std::forward<M>(obj));
    }
 
    template <class M> std::pair<iterator, bool> insert_or_assign(key_type &&k, M &&obj)
    {
      return m_ht.insert_or_assign(std::move(k), std::forward<M>(obj));
    }
 
    template <class M> iterator insert_or_assign(const_iterator hint, const key_type &k, M &&obj)
    {
      return m_ht.insert_or_assign(hint, k, std::forward<M>(obj));
    }
 
    template <class M> iterator insert_or_assign(const_iterator hint, key_type &&k, M &&obj)
    {
      return m_ht.insert_or_assign(hint, std::move(k), std::forward<M>(obj));
    }
 
    /**
     * Due to the way elements are stored, emplace will need to move or copy the key-value once.
     * The method is equivalent to insert(value_type(std::forward<Args>(args)...));
     *
     * Mainly here for compatibility with the std::unordered_map interface.
     */
    template <class... Args> std::pair<iterator, bool> emplace(Args &&... args)
    {
      return m_ht.emplace(std::forward<Args>(args)...);
    }
 
    /**
     * Due to the way elements are stored, emplace_hint will need to move or copy the key-value
     * once. The method is equivalent to insert(hint, value_type(std::forward<Args>(args)...));
     *
     * Mainly here for compatibility with the std::unordered_map interface.
     */
    template <class... Args> iterator emplace_hint(const_iterator hint, Args &&... args)
    {
      return m_ht.emplace_hint(hint, std::forward<Args>(args)...);
    }
 
    template <class... Args>
    std::pair<iterator, bool> try_emplace(const key_type &k, Args &&... args)
    {
      return m_ht.try_emplace(k, std::forward<Args>(args)...);
    }
 
    template <class... Args> std::pair<iterator, bool> try_emplace(key_type &&k, Args &&... args)
    {
      return m_ht.try_emplace(std::move(k), std::forward<Args>(args)...);
    }
 
    template <class... Args>
    iterator try_emplace(const_iterator hint, const key_type &k, Args &&... args)
    {
      return m_ht.try_emplace(hint, k, std::forward<Args>(args)...);
    }
 
    template <class... Args>
    iterator try_emplace(const_iterator hint, key_type &&k, Args &&... args)
    {
      return m_ht.try_emplace(hint, std::move(k), std::forward<Args>(args)...);
    }
 
    iterator  erase(iterator pos) { return m_ht.erase(pos); }
    iterator  erase(const_iterator pos) { return m_ht.erase(pos); }
    iterator  erase(const_iterator first, const_iterator last) { return m_ht.erase(first, last); }
    size_type erase(const key_type &key) { return m_ht.erase(key); }
 
    /**
     * Use the hash value 'precalculated_hash' instead of hashing the key. The hash value should be
     * the same as hash_function()(key). Useful to speed-up the lookup to the value if you already
     * have the hash.
     */
    size_type erase(const key_type &key, std::size_t precalculated_hash)
    {
      return m_ht.erase(key, precalculated_hash);
    }
 
    /**
     * This overload only participates in the overload resolution if the typedef
     * KeyEqual::is_transparent exists. If so, K must be hashable and comparable to Key.
     */
    template <class K, class KE = KeyEqual,
              typename std::enable_if<has_is_transparent<KE>::value>::type * = nullptr>
    size_type erase(const K &key)
    {
      return m_ht.erase(key);
    }
 
    /**
     * @copydoc erase(const K& key)
     *
     * Use the hash value 'precalculated_hash' instead of hashing the key. The hash value should be
     * the same as hash_function()(key). Useful to speed-up the lookup to the value if you already
     * have the hash.
     */
    template <class K, class KE = KeyEqual,
              typename std::enable_if<has_is_transparent<KE>::value>::type * = nullptr>
    size_type erase(const K &key, std::size_t precalculated_hash)
    {
      return m_ht.erase(key, precalculated_hash);
    }
 
    void swap(hopscotch_map &other) { other.m_ht.swap(m_ht); }
 
    /*
     * Lookup
     */
    T &at(const Key &key) { return m_ht.at(key); }
 
    /**
     * Use the hash value 'precalculated_hash' instead of hashing the key. The hash value should be
     * the same as hash_function()(key). Useful to speed-up the lookup if you already have the
     * hash.
     */
    T &at(const Key &key, std::size_t precalculated_hash)
    {
      return m_ht.at(key, precalculated_hash);
    }
 
    const T &at(const Key &key) const { return m_ht.at(key); }
 
    /**
     * @copydoc at(const Key& key, std::size_t precalculated_hash)
     */
    const T &at(const Key &key, std::size_t precalculated_hash) const
    {
      return m_ht.at(key, precalculated_hash);
    }
 
    /**
     * This overload only participates in the overload resolution if the typedef
     * KeyEqual::is_transparent exists. If so, K must be hashable and comparable to Key.
     */
    template <class K, class KE = KeyEqual,
              typename std::enable_if<has_is_transparent<KE>::value>::type * = nullptr>
    T &at(const K &key)
    {
      return m_ht.at(key);
    }
 
    /**
     * @copydoc at(const K& key)
     *
     * Use the hash value 'precalculated_hash' instead of hashing the key. The hash value should be
     * the same as hash_function()(key). Useful to speed-up the lookup if you already have the
     * hash.
     */
    template <class K, class KE = KeyEqual,
              typename std::enable_if<has_is_transparent<KE>::value>::type * = nullptr>
    T &at(const K &key, std::size_t precalculated_hash)
    {
      return m_ht.at(key, precalculated_hash);
    }
 
    /**
     * @copydoc at(const K& key)
     */
    template <class K, class KE = KeyEqual,
              typename std::enable_if<has_is_transparent<KE>::value>::type * = nullptr>
    const T &at(const K &key) const
    {
      return m_ht.at(key);
    }
 
    /**
     * @copydoc at(const K& key, std::size_t precalculated_hash)
     */
    template <class K, class KE = KeyEqual,
              typename std::enable_if<has_is_transparent<KE>::value>::type * = nullptr>
    const T &at(const K &key, std::size_t precalculated_hash) const
    {
      return m_ht.at(key, precalculated_hash);
    }
 
    T &operator[](const Key &key) { return m_ht[key]; }
    T &operator[](Key &&key) { return m_ht[std::move(key)]; }
 
    size_type count(const Key &key) const { return m_ht.count(key); }
 
    /**
     * Use the hash value 'precalculated_hash' instead of hashing the key. The hash value should be
     * the same as hash_function()(key). Useful to speed-up the lookup if you already have the
     * hash.
     */
    size_type count(const Key &key, std::size_t precalculated_hash) const
    {
      return m_ht.count(key, precalculated_hash);
    }
 
    /**
     * This overload only participates in the overload resolution if the typedef
     * KeyEqual::is_transparent exists. If so, K must be hashable and comparable to Key.
     */
    template <class K, class KE = KeyEqual,
              typename std::enable_if<has_is_transparent<KE>::value>::type * = nullptr>
    size_type count(const K &key) const
    {
      return m_ht.count(key);
    }
 
    /**
     * @copydoc count(const K& key) const
     *
     * Use the hash value 'precalculated_hash' instead of hashing the key. The hash value should be
     * the same as hash_function()(key). Useful to speed-up the lookup if you already have the
     * hash.
     */
    template <class K, class KE = KeyEqual,
              typename std::enable_if<has_is_transparent<KE>::value>::type * = nullptr>
    size_type count(const K &key, std::size_t precalculated_hash) const
    {
      return m_ht.count(key, precalculated_hash);
    }
 
    iterator find(const Key &key) { return m_ht.find(key); }
 
    /**
     * Use the hash value 'precalculated_hash' instead of hashing the key. The hash value should be
     * the same as hash_function()(key). Useful to speed-up the lookup if you already have the
     * hash.
     */
    iterator find(const Key &key, std::size_t precalculated_hash)
    {
      return m_ht.find(key, precalculated_hash);
    }
 
    const_iterator find(const Key &key) const { return m_ht.find(key); }
 
    /**
     * @copydoc find(const Key& key, std::size_t precalculated_hash)
     */
    const_iterator find(const Key &key, std::size_t precalculated_hash) const
    {
      return m_ht.find(key, precalculated_hash);
    }
 
    /**
     * This overload only participates in the overload resolution if the typedef
     * KeyEqual::is_transparent exists. If so, K must be hashable and comparable to Key.
     */
    template <class K, class KE = KeyEqual,
              typename std::enable_if<has_is_transparent<KE>::value>::type * = nullptr>
    iterator find(const K &key)
    {
      return m_ht.find(key);
    }
 
    /**
     * @copydoc find(const K& key)
     *
     * Use the hash value 'precalculated_hash' instead of hashing the key. The hash value should be
     * the same as hash_function()(key). Useful to speed-up the lookup if you already have the
     * hash.
     */
    template <class K, class KE = KeyEqual,
              typename std::enable_if<has_is_transparent<KE>::value>::type * = nullptr>
    iterator find(const K &key, std::size_t precalculated_hash)
    {
      return m_ht.find(key, precalculated_hash);
    }
 
    /**
     * @copydoc find(const K& key)
     */
    template <class K, class KE = KeyEqual,
              typename std::enable_if<has_is_transparent<KE>::value>::type * = nullptr>
    const_iterator find(const K &key) const
    {
      return m_ht.find(key);
    }
 
    /**
     * @copydoc find(const K& key)
     *
     * Use the hash value 'precalculated_hash' instead of hashing the key. The hash value should be
     * the same as hash_function()(key). Useful to speed-up the lookup if you already have the
     * hash.
     */
    template <class K, class KE = KeyEqual,
              typename std::enable_if<has_is_transparent<KE>::value>::type * = nullptr>
    const_iterator find(const K &key, std::size_t precalculated_hash) const
    {
      return m_ht.find(key, precalculated_hash);
    }
 
    bool contains(const Key &key) const { return m_ht.contains(key); }
 
    /**
     * Use the hash value 'precalculated_hash' instead of hashing the key. The hash value should be
     * the same as hash_function()(key). Useful to speed-up the lookup if you already have the
     * hash.
     */
    bool contains(const Key &key, std::size_t precalculated_hash) const
    {
      return m_ht.contains(key, precalculated_hash);
    }
 
    /**
     * This overload only participates in the overload resolution if the typedef
     * KeyEqual::is_transparent exists. If so, K must be hashable and comparable to Key.
     */
    template <class K, class KE = KeyEqual,
              typename std::enable_if<has_is_transparent<KE>::value>::type * = nullptr>
    bool contains(const K &key) const
    {
      return m_ht.contains(key);
    }
 
    /**
     * @copydoc contains(const K& key) const
     *
     * Use the hash value 'precalculated_hash' instead of hashing the key. The hash value should be
     * the same as hash_function()(key). Useful to speed-up the lookup if you already have the
     * hash.
     */
    template <class K, class KE = KeyEqual,
              typename std::enable_if<has_is_transparent<KE>::value>::type * = nullptr>
    bool contains(const K &key, std::size_t precalculated_hash) const
    {
      return m_ht.contains(key, precalculated_hash);
    }
 
    std::pair<iterator, iterator> equal_range(const Key &key) { return m_ht.equal_range(key); }
 
    /**
     * Use the hash value 'precalculated_hash' instead of hashing the key. The hash value should be
     * the same as hash_function()(key). Useful to speed-up the lookup if you already have the
     * hash.
     */
    std::pair<iterator, iterator> equal_range(const Key &key, std::size_t precalculated_hash)
    {
      return m_ht.equal_range(key, precalculated_hash);
    }
 
    std::pair<const_iterator, const_iterator> equal_range(const Key &key) const
    {
      return m_ht.equal_range(key);
    }
 
    /**
     * @copydoc equal_range(const Key& key, std::size_t precalculated_hash)
     */
    std::pair<const_iterator, const_iterator> equal_range(const Key & key,
                                                          std::size_t precalculated_hash) const
    {
      return m_ht.equal_range(key, precalculated_hash);
    }
 
    /**
     * This overload only participates in the overload resolution if the typedef
     * KeyEqual::is_transparent exists. If so, K must be hashable and comparable to Key.
     */
    template <class K, class KE = KeyEqual,
              typename std::enable_if<has_is_transparent<KE>::value>::type * = nullptr>
    std::pair<iterator, iterator> equal_range(const K &key)
    {
      return m_ht.equal_range(key);
    }
 
    /**
     * @copydoc equal_range(const K& key)
     *
     * Use the hash value 'precalculated_hash' instead of hashing the key. The hash value should be
     * the same as hash_function()(key). Useful to speed-up the lookup if you already have the
     * hash.
     */
    template <class K, class KE = KeyEqual,
              typename std::enable_if<has_is_transparent<KE>::value>::type * = nullptr>
    std::pair<iterator, iterator> equal_range(const K &key, std::size_t precalculated_hash)
    {
      return m_ht.equal_range(key, precalculated_hash);
    }
 
    /**
     * @copydoc equal_range(const K& key)
     */
    template <class K, class KE = KeyEqual,
              typename std::enable_if<has_is_transparent<KE>::value>::type * = nullptr>
    std::pair<const_iterator, const_iterator> equal_range(const K &key) const
    {
      return m_ht.equal_range(key);
    }
 
    /**
     * @copydoc equal_range(const K& key, std::size_t precalculated_hash)
     */
    template <class K, class KE = KeyEqual,
              typename std::enable_if<has_is_transparent<KE>::value>::type * = nullptr>
    std::pair<const_iterator, const_iterator> equal_range(const K &   key,
                                                          std::size_t precalculated_hash) const
    {
      return m_ht.equal_range(key, precalculated_hash);
    }
 
    /*
     * Bucket interface
     */
    size_type bucket_count() const { return m_ht.bucket_count(); }
    size_type max_bucket_count() const { return m_ht.max_bucket_count(); }
 
    /*
     *  Hash policy
     */
    float load_factor() const { return m_ht.load_factor(); }
    float max_load_factor() const { return m_ht.max_load_factor(); }
    void  max_load_factor(float ml) { m_ht.max_load_factor(ml); }
 
    void rehash(size_type count_) { m_ht.rehash(count_); }
    void reserve(size_type count_) { m_ht.reserve(count_); }
 
    /*
     * Observers
     */
    hasher    hash_function() const { return m_ht.hash_function(); }
    key_equal key_eq() const { return m_ht.key_eq(); }
 
    /*
     * Other
     */
 
    /**
     * Convert a const_iterator to an iterator.
     */
    iterator mutable_iterator(const_iterator pos) { return m_ht.mutable_iterator(pos); }
 
    size_type overflow_size() const noexcept { return m_ht.overflow_size(); }
 
    friend bool operator==(const hopscotch_map &lhs, const hopscotch_map &rhs)
    {
      if (lhs.size() != rhs.size()) {
        return false;
      }
 
      for (const auto &element_lhs : lhs) {
        const auto it_element_rhs = rhs.find(element_lhs.first);
        if (it_element_rhs == rhs.cend() || element_lhs.second != it_element_rhs->second) {
          return false;
        }
      }
 
      return true;
    }
 
    friend bool operator!=(const hopscotch_map &lhs, const hopscotch_map &rhs)
    {
      return !operator==(lhs, rhs);
    }
 
    friend void swap(hopscotch_map &lhs, hopscotch_map &rhs) { lhs.swap(rhs); }
 
  private:
    ht m_ht;
  };
 
  /**
   * Same as `tsl::hopscotch_map<Key, T, Hash, KeyEqual, Allocator, NeighborhoodSize, StoreHash,
   * tsl::hh::prime_growth_policy>`.
   */
  template <class Key, class T, class Hash = std::hash<Key>, class KeyEqual = std::equal_to<Key>,
            class Allocator = std::allocator<std::pair<Key, T>>, unsigned int NeighborhoodSize = 62,
            bool StoreHash = false>
  using hopscotch_pg_map = hopscotch_map<Key, T, Hash, KeyEqual, Allocator, NeighborhoodSize,
                                         StoreHash, tsl::hh::prime_growth_policy>;
 
} // end namespace tsl
 
#endif