LEANN/packages/leann-backend-diskann/third_party/DiskANN/include/tsl/sparse_map.h

/**
 * MIT License
 *
 * Copyright (c) 2017 Thibaut Goetghebuer-Planchon <tessil@gmx.com>
 *
 * 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_SPARSE_MAP_H
#define TSL_SPARSE_MAP_H

#include <cstddef>
#include <functional>
#include <initializer_list>
#include <memory>
#include <type_traits>
#include <utility>

#include "sparse_hash.h"

namespace tsl {

/**
 * Implementation of a sparse hash map using open-addressing with quadratic
 * probing. The goal on the hash map is to be the most memory efficient
 * possible, even at low load factor, while keeping reasonable performances.
 *
 * `GrowthPolicy` defines how the map grows and consequently how a hash value is
 * mapped to a bucket. By default the map uses
 * `tsl::sh::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. Other growth policies are available and you may define
 * your own growth policy, check `tsl::sh::power_of_two_growth_policy` for the
 * interface.
 *
 * `ExceptionSafety` defines the exception guarantee provided by the class. By
 * default only the basic exception safety is guaranteed which mean that all
 * resources used by the hash map will be freed (no memory leaks) but the hash
 * map may end-up in an undefined state if an exception is thrown (undefined
 * here means that some elements may be missing). This can ONLY happen on rehash
 * (either on insert or if `rehash` is called explicitly) and will occur if the
 * Allocator can't allocate memory (`std::bad_alloc`) or if the copy constructor
 * (when a nothrow move constructor is not available) throws an exception. This
 * can be avoided by calling `reserve` beforehand. This basic guarantee is
 * similar to the one of `google::sparse_hash_map` and `spp::sparse_hash_map`.
 * It is possible to ask for the strong exception guarantee with
 * `tsl::sh::exception_safety::strong`, the drawback is that the map will be
 * slower on rehashes and will also need more memory on rehashes.
 *
 * `Sparsity` defines how much the hash set will compromise between insertion
 * speed and memory usage. A high sparsity means less memory usage but longer
 * insertion times, and vice-versa for low sparsity. The default
 * `tsl::sh::sparsity::medium` sparsity offers a good compromise. It doesn't
 * change the lookup speed.
 *
 * `Key` and `T` must be nothrow move constructible and/or copy constructible.
 *
 * If the destructor of `Key` or `T` throws an exception, the 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.
 *  - erase: always invalidate the iterators.
 */
template <class Key, class T, class Hash = std::hash<Key>,
          class KeyEqual = std::equal_to<Key>,
          class Allocator = std::allocator<std::pair<Key, T>>,
          class GrowthPolicy = tsl::sh::power_of_two_growth_policy<2>,
          tsl::sh::exception_safety ExceptionSafety =
              tsl::sh::exception_safety::basic,
          tsl::sh::sparsity Sparsity = tsl::sh::sparsity::medium>
class sparse_map {
 private:
  template <typename U>
  using has_is_transparent = tsl::detail_sparse_hash::has_is_transparent<U>;

  class KeySelect {
   public:
    using key_type = Key;

    const key_type &operator()(
        const std::pair<Key, T> &key_value) const noexcept {
      return key_value.first;
    }

    key_type &operator()(std::pair<Key, T> &key_value) noexcept {
      return key_value.first;
    }
  };

  class ValueSelect {
   public:
    using value_type = T;

    const value_type &operator()(
        const std::pair<Key, T> &key_value) const noexcept {
      return key_value.second;
    }

    value_type &operator()(std::pair<Key, T> &key_value) noexcept {
      return key_value.second;
    }
  };

  using ht = detail_sparse_hash::sparse_hash<
      std::pair<Key, T>, KeySelect, ValueSelect, Hash, KeyEqual, Allocator,
      GrowthPolicy, ExceptionSafety, Sparsity, tsl::sh::probing::quadratic>;

 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;

 public:
  /*
   * Constructors
   */
  sparse_map() : sparse_map(ht::DEFAULT_INIT_BUCKET_COUNT) {}

  explicit sparse_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) {}

  sparse_map(size_type bucket_count, const Allocator &alloc)
      : sparse_map(bucket_count, Hash(), KeyEqual(), alloc) {}

  sparse_map(size_type bucket_count, const Hash &hash, const Allocator &alloc)
      : sparse_map(bucket_count, hash, KeyEqual(), alloc) {}

  explicit sparse_map(const Allocator &alloc)
      : sparse_map(ht::DEFAULT_INIT_BUCKET_COUNT, alloc) {}

  template <class InputIt>
  sparse_map(InputIt first, InputIt last,
             size_type bucket_count = ht::DEFAULT_INIT_BUCKET_COUNT,
             const Hash &hash = Hash(), const KeyEqual &equal = KeyEqual(),
             const Allocator &alloc = Allocator())
      : sparse_map(bucket_count, hash, equal, alloc) {
    insert(first, last);
  }

  template <class InputIt>
  sparse_map(InputIt first, InputIt last, size_type bucket_count,
             const Allocator &alloc)
      : sparse_map(first, last, bucket_count, Hash(), KeyEqual(), alloc) {}

  template <class InputIt>
  sparse_map(InputIt first, InputIt last, size_type bucket_count,
             const Hash &hash, const Allocator &alloc)
      : sparse_map(first, last, bucket_count, hash, KeyEqual(), alloc) {}

  sparse_map(std::initializer_list<value_type> init,
             size_type bucket_count = ht::DEFAULT_INIT_BUCKET_COUNT,
             const Hash &hash = Hash(), const KeyEqual &equal = KeyEqual(),
             const Allocator &alloc = Allocator())
      : sparse_map(init.begin(), init.end(), bucket_count, hash, equal, alloc) {
  }

  sparse_map(std::initializer_list<value_type> init, size_type bucket_count,
             const Allocator &alloc)
      : sparse_map(init.begin(), init.end(), bucket_count, Hash(), KeyEqual(),
                   alloc) {}

  sparse_map(std::initializer_list<value_type> init, size_type bucket_count,
             const Hash &hash, const Allocator &alloc)
      : sparse_map(init.begin(), init.end(), bucket_count, hash, KeyEqual(),
                   alloc) {}

  sparse_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.emplace(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(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.emplace_hint(hint, std::forward<P>(value));
  }

  iterator insert(const_iterator hint, value_type &&value) {
    return m_ht.insert_hint(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(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(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)`, otherwise the
   * behaviour is undefined. Useful to speed-up the lookup 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)`, otherwise the
   * behaviour is undefined. 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 erase(const K &key, std::size_t precalculated_hash) {
    return m_ht.erase(key, precalculated_hash);
  }

  void swap(sparse_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)`, otherwise the
   * behaviour is undefined. 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)`, otherwise the
   * behaviour is undefined. 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)`, otherwise the
   * behaviour is undefined. 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)`, otherwise the
   * behaviour is undefined. 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)`, otherwise the
   * behaviour is undefined. 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)`, otherwise the
   * behaviour is undefined. 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)`, otherwise the
   * behaviour is undefined. 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)`, otherwise the
   * behaviour is undefined. 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)`, otherwise the
   * behaviour is undefined. 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);
  }

  /**
   * Serialize the map through the `serializer` parameter.
   *
   * The `serializer` parameter must be a function object that supports the
   * following call:
   *  - `template<typename U> void operator()(const U& value);` where the types
   * `std::uint64_t`, `float` and `std::pair<Key, T>` must be supported for U.
   *
   * The implementation leaves binary compatibility (endianness, IEEE 754 for
   * floats, ...) of the types it serializes in the hands of the `Serializer`
   * function object if compatibility is required.
   */
  template <class Serializer>
  void serialize(Serializer &serializer) const {
    m_ht.serialize(serializer);
  }

  /**
   * Deserialize a previously serialized map through the `deserializer`
   * parameter.
   *
   * The `deserializer` parameter must be a function object that supports the
   * following calls:
   *  - `template<typename U> U operator()();` where the types `std::uint64_t`,
   * `float` and `std::pair<Key, T>` must be supported for U.
   *
   * If the deserialized hash map type is hash compatible with the serialized
   * map, the deserialization process can be sped up by setting
   * `hash_compatible` to true. To be hash compatible, the Hash, KeyEqual and
   * GrowthPolicy must behave the same way than the ones used on the serialized
   * map. The `std::size_t` must also be of the same size as the one on the
   * platform used to serialize the map. If these criteria are not met, the
   * behaviour is undefined with `hash_compatible` sets to true.
   *
   * The behaviour is undefined if the type `Key` and `T` of the `sparse_map`
   * are not the same as the types used during serialization.
   *
   * The implementation leaves binary compatibility (endianness, IEEE 754 for
   * floats, size of int, ...) of the types it deserializes in the hands of the
   * `Deserializer` function object if compatibility is required.
   */
  template <class Deserializer>
  static sparse_map deserialize(Deserializer &deserializer,
                                bool hash_compatible = false) {
    sparse_map map(0);
    map.m_ht.deserialize(deserializer, hash_compatible);

    return map;
  }

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

  friend void swap(sparse_map &lhs, sparse_map &rhs) { lhs.swap(rhs); }

 private:
  ht m_ht;
};

/**
 * Same as `tsl::sparse_map<Key, T, Hash, KeyEqual, Allocator,
 * tsl::sh::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>>>
using sparse_pg_map =
    sparse_map<Key, T, Hash, KeyEqual, Allocator, tsl::sh::prime_growth_policy>;

}  // end namespace tsl

#endif