robin_map.h

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/**
 * 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 PXR_TSL_ROBIN_MAP_H
#define PXR_TSL_ROBIN_MAP_H

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

#include "robin_hash.h"

// Pixar modification, modify namespace for isolation.
#include "pxr/pxr.h"

PXR_NAMESPACE_OPEN_SCOPE

namespace pxr_tsl {

/**
 * Implementation of a hash map using open-addressing and the robin hood hashing
 * algorithm with backward shift deletion.
 *
 * For operations modifying the hash map (insert, erase, rehash, ...), the
 * strong exception guarantee is only guaranteed when the expression
 * `std::is_nothrow_swappable<std::pair<Key, T>>::value &&
 * std::is_nothrow_move_constructible<std::pair<Key, T>>::value` is true,
 * otherwise if an exception is thrown during the swap or the move, the hash map
 * may end up in a undefined state. Per the standard a `Key` or `T` with a
 * noexcept copy constructor and no move constructor also satisfies the
 * `std::is_nothrow_move_constructible<std::pair<Key, T>>::value` criterion (and
 * will thus guarantee the strong exception for the map).
 *
 * When `StoreHash` is true, 32 bits of the hash are stored alongside the
 * values. It can improve the performance during lookups if the `KeyEqual`
 * function takes time (if it engenders a cache-miss for example) as we then
 * compare the stored hashes before comparing the keys. When
 * `pxr_tsl::rh::power_of_two_growth_policy` is used as `GrowthPolicy`, it may also
 * speed-up the rehash process as we can avoid to recalculate the hash. When it
 * is detected that storing the hash will not incur any memory penalty due to
 * alignment (i.e. `sizeof(pxr_tsl::detail_robin_hash::bucket_entry<ValueType,
 * true>) == sizeof(pxr_tsl::detail_robin_hash::bucket_entry<ValueType, false>)`)
 * and `pxr_tsl::rh::power_of_two_growth_policy` is used, the hash will be stored
 * even if `StoreHash` is false so that we can speed-up the rehash (but it will
 * not be used on lookups unless `StoreHash` is true).
 *
 * `GrowthPolicy` defines how the map grows and consequently how a hash value is
 * mapped to a bucket. By default the map uses
 * `pxr_tsl::rh::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 `pxr_tsl::rh::power_of_two_growth_policy` for the
 * interface.
 *
 * `std::pair<Key, T>` must be swappable.
 *
 * `Key` and `T` must be copy and/or move 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>>,
          bool StoreHash = false,
          class GrowthPolicy = pxr_tsl::rh::power_of_two_growth_policy<2>>
class robin_map {
 private:
  template <typename U>
  using has_is_transparent = pxr_tsl::detail_robin_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_robin_hash::robin_hash<std::pair<Key, T>, KeySelect,
                                           ValueSelect, Hash, KeyEqual,
                                           Allocator, StoreHash, GrowthPolicy>;

 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
   */
  robin_map() : robin_map(ht::DEFAULT_INIT_BUCKETS_SIZE) {}

  explicit robin_map(size_type bucket_count, const Hash& hash = Hash(),
                     const KeyEqual& equal = KeyEqual(),
                     const Allocator& alloc = Allocator())
      : m_ht(bucket_count, hash, equal, alloc) {}

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

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

  explicit robin_map(const Allocator& alloc)
      : robin_map(ht::DEFAULT_INIT_BUCKETS_SIZE, alloc) {}

  template <class InputIt>
  robin_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())
      : robin_map(bucket_count, hash, equal, alloc) {
    insert(first, last);
  }

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

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

  robin_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())
      : robin_map(init.begin(), init.end(), bucket_count, hash, equal, alloc) {}

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

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

  robin_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); }

  /**
   * Erase the element at position 'pos'. In contrast to the regular erase()
   * function, erase_fast() does not return an iterator. This allows it to be
   * faster especially in hash tables with a low load factor, where finding the
   * next nonempty bucket would be costly.
   */
  void erase_fast(iterator pos) { return m_ht.erase_fast(pos); }

  /**
   * 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(robin_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 min_load_factor() const { return m_ht.min_load_factor(); }
  float max_load_factor() const { return m_ht.max_load_factor(); }

  /**
   * Set the `min_load_factor` to `ml`. When the `load_factor` of the map goes
   * below `min_load_factor` after some erase operations, the map will be
   * shrunk when an insertion occurs. The erase method itself never shrinks
   * the map.
   *
   * The default value of `min_load_factor` is 0.0f, the map never shrinks by
   * default.
   */
  void min_load_factor(float ml) { m_ht.min_load_factor(ml); }
  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::int16_t`, `std::uint32_t`, `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 call:
   *  - `template<typename U> U operator()();` where the types `std::int16_t`,
   * `std::uint32_t`, `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 and the StoreHash must have the same value. 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 `robin_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 robin_map deserialize(Deserializer& deserializer,
                               bool hash_compatible = false) {
    robin_map map(0);
    map.m_ht.deserialize(deserializer, hash_compatible);

    return map;
  }

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

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

 private:
  ht m_ht;
};

/**
 * Same as `pxr_tsl::robin_map<Key, T, Hash, KeyEqual, Allocator, StoreHash,
 * pxr_tsl::rh::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>>,
          bool StoreHash = false>
using robin_pg_map = robin_map<Key, T, Hash, KeyEqual, Allocator, StoreHash,
                               pxr_tsl::rh::prime_growth_policy>;

}  // end namespace pxr_tsl

PXR_NAMESPACE_CLOSE_SCOPE

#endif