// Copyright 2017 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef BASE_CONTAINERS_FLAT_MAP_H_
#define BASE_CONTAINERS_FLAT_MAP_H_
#include <functional>
#include <tuple>
#include <utility>
#include "base/containers/flat_tree.h"
#include "base/logging.h"
#include "base/template_util.h"
namespace base {
namespace internal {
// An implementation of the flat_tree GetKeyFromValue template parameter that
// extracts the key as the first element of a pair.
template <class Key, class Mapped>
struct GetKeyFromValuePairFirst {
const Key& operator()(const std::pair<Key, Mapped>& p) const {
return p.first;
}
};
} // namespace internal
// flat_map is a container with a std::map-like interface that stores its
// contents in a sorted vector.
//
// Please see //base/containers/README.md for an overview of which container
// to select.
//
// PROS
//
// - Good memory locality.
// - Low overhead, especially for smaller maps.
// - Performance is good for more workloads than you might expect (see
// overview link above).
// - Supports C++14 map interface.
//
// CONS
//
// - Inserts and removals are O(n).
//
// IMPORTANT NOTES
//
// - Iterators are invalidated across mutations.
// - If possible, construct a flat_map in one operation by inserting into
// a std::vector and moving that vector into the flat_map constructor.
//
// QUICK REFERENCE
//
// Most of the core functionality is inherited from flat_tree. Please see
// flat_tree.h for more details for most of these functions. As a quick
// reference, the functions available are:
//
// Constructors (inputs need not be sorted):
// flat_map(InputIterator first, InputIterator last,
// FlatContainerDupes = KEEP_FIRST_OF_DUPES,
// const Compare& compare = Compare());
// flat_map(const flat_map&);
// flat_map(flat_map&&);
// flat_map(std::vector<value_type>,
// FlatContainerDupes = KEEP_FIRST_OF_DUPES,
// const Compare& compare = Compare()); // Re-use storage.
// flat_map(std::initializer_list<value_type> ilist,
// FlatContainerDupes = KEEP_FIRST_OF_DUPES,
// const Compare& comp = Compare());
//
// Assignment functions:
// flat_map& operator=(const flat_map&);
// flat_map& operator=(flat_map&&);
// flat_map& operator=(initializer_list<value_type>);
//
// Memory management functions:
// void reserve(size_t);
// size_t capacity() const;
// void shrink_to_fit();
//
// Size management functions:
// void clear();
// size_t size() const;
// size_t max_size() const;
// bool empty() const;
//
// Iterator functions:
// iterator begin();
// const_iterator begin() const;
// const_iterator cbegin() const;
// iterator end();
// const_iterator end() const;
// const_iterator cend() const;
// reverse_iterator rbegin();
// const reverse_iterator rbegin() const;
// const_reverse_iterator crbegin() const;
// reverse_iterator rend();
// const_reverse_iterator rend() const;
// const_reverse_iterator crend() const;
//
// Insert and accessor functions:
// mapped_type& operator[](const key_type&);
// mapped_type& operator[](key_type&&);
// pair<iterator, bool> insert(const value_type&);
// pair<iterator, bool> insert(value_type&&);
// iterator insert(const_iterator hint, const value_type&);
// iterator insert(const_iterator hint, value_type&&);
// void insert(InputIterator first, InputIterator last,
// FlatContainerDupes = KEEP_FIRST_OF_DUPES);
// pair<iterator, bool> insert_or_assign(K&&, M&&);
// iterator insert_or_assign(const_iterator hint, K&&, M&&);
// pair<iterator, bool> emplace(Args&&...);
// iterator emplace_hint(const_iterator, Args&&...);
// pair<iterator, bool> try_emplace(K&&, Args&&...);
// iterator try_emplace(const_iterator hint, K&&, Args&&...);
//
// Erase functions:
// iterator erase(iterator);
// iterator erase(const_iterator);
// iterator erase(const_iterator first, const_iterator& last);
// template <class K> size_t erase(const K& key);
//
// Comparators (see std::map documentation).
// key_compare key_comp() const;
// value_compare value_comp() const;
//
// Search functions:
// template <typename K> size_t count(const K&) const;
// template <typename K> iterator find(const K&);
// template <typename K> const_iterator find(const K&) const;
// template <typename K> pair<iterator, iterator> equal_range(const K&);
// template <typename K> iterator lower_bound(const K&);
// template <typename K> const_iterator lower_bound(const K&) const;
// template <typename K> iterator upper_bound(const K&);
// template <typename K> const_iterator upper_bound(const K&) const;
//
// General functions:
// void swap(flat_map&&);
//
// Non-member operators:
// bool operator==(const flat_map&, const flat_map);
// bool operator!=(const flat_map&, const flat_map);
// bool operator<(const flat_map&, const flat_map);
// bool operator>(const flat_map&, const flat_map);
// bool operator>=(const flat_map&, const flat_map);
// bool operator<=(const flat_map&, const flat_map);
//
template <class Key, class Mapped, class Compare = std::less<>>
class flat_map : public ::base::internal::flat_tree<
Key,
std::pair<Key, Mapped>,
::base::internal::GetKeyFromValuePairFirst<Key, Mapped>,
Compare> {
private:
using tree = typename ::base::internal::flat_tree<
Key,
std::pair<Key, Mapped>,
::base::internal::GetKeyFromValuePairFirst<Key, Mapped>,
Compare>;
public:
using key_type = typename tree::key_type;
using mapped_type = Mapped;
using value_type = typename tree::value_type;
using iterator = typename tree::iterator;
using const_iterator = typename tree::const_iterator;
// --------------------------------------------------------------------------
// Lifetime and assignments.
//
// Note: we could do away with these constructors, destructor and assignment
// operator overloads by inheriting |tree|'s, but this breaks the GCC build
// due to https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84782 (see
// https://crbug.com/837221).
flat_map() = default;
explicit flat_map(const Compare& comp);
template <class InputIterator>
flat_map(InputIterator first,
InputIterator last,
FlatContainerDupes dupe_handling = KEEP_FIRST_OF_DUPES,
const Compare& comp = Compare());
flat_map(const flat_map&) = default;
flat_map(flat_map&&) noexcept = default;
flat_map(std::vector<value_type> items,
FlatContainerDupes dupe_handling = KEEP_FIRST_OF_DUPES,
const Compare& comp = Compare());
flat_map(std::initializer_list<value_type> ilist,
FlatContainerDupes dupe_handling = KEEP_FIRST_OF_DUPES,
const Compare& comp = Compare());
~flat_map() = default;
flat_map& operator=(const flat_map&) = default;
flat_map& operator=(flat_map&&) = default;
// Takes the first if there are duplicates in the initializer list.
flat_map& operator=(std::initializer_list<value_type> ilist);
// --------------------------------------------------------------------------
// Map-specific insert operations.
//
// Normal insert() functions are inherited from flat_tree.
//
// Assume that every operation invalidates iterators and references.
// Insertion of one element can take O(size).
mapped_type& operator[](const key_type& key);
mapped_type& operator[](key_type&& key);
template <class K, class M>
std::pair<iterator, bool> insert_or_assign(K&& key, M&& obj);
template <class K, class M>
iterator insert_or_assign(const_iterator hint, K&& key, M&& obj);
template <class K, class... Args>
std::enable_if_t<std::is_constructible<key_type, K&&>::value,
std::pair<iterator, bool>>
try_emplace(K&& key, Args&&... args);
template <class K, class... Args>
std::enable_if_t<std::is_constructible<key_type, K&&>::value, iterator>
try_emplace(const_iterator hint, K&& key, Args&&... args);
// --------------------------------------------------------------------------
// General operations.
//
// Assume that swap invalidates iterators and references.
void swap(flat_map& other) noexcept;
friend void swap(flat_map& lhs, flat_map& rhs) noexcept { lhs.swap(rhs); }
};
// ----------------------------------------------------------------------------
// Lifetime.
template <class Key, class Mapped, class Compare>
flat_map<Key, Mapped, Compare>::flat_map(const Compare& comp) : tree(comp) {}
template <class Key, class Mapped, class Compare>
template <class InputIterator>
flat_map<Key, Mapped, Compare>::flat_map(InputIterator first,
InputIterator last,
FlatContainerDupes dupe_handling,
const Compare& comp)
: tree(first, last, dupe_handling, comp) {}
template <class Key, class Mapped, class Compare>
flat_map<Key, Mapped, Compare>::flat_map(std::vector<value_type> items,
FlatContainerDupes dupe_handling,
const Compare& comp)
: tree(std::move(items), dupe_handling, comp) {}
template <class Key, class Mapped, class Compare>
flat_map<Key, Mapped, Compare>::flat_map(
std::initializer_list<value_type> ilist,
FlatContainerDupes dupe_handling,
const Compare& comp)
: flat_map(std::begin(ilist), std::end(ilist), dupe_handling, comp) {}
// ----------------------------------------------------------------------------
// Assignments.
template <class Key, class Mapped, class Compare>
auto flat_map<Key, Mapped, Compare>::operator=(
std::initializer_list<value_type> ilist) -> flat_map& {
// When https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84782 gets fixed, we
// need to remember to inherit tree::operator= to prevent
// flat_map<...> x;
// x = {...};
// from first creating a flat_map and then move assigning it. This most
// likely would be optimized away but still affects our debug builds.
tree::operator=(ilist);
return *this;
}
// ----------------------------------------------------------------------------
// Insert operations.
template <class Key, class Mapped, class Compare>
auto flat_map<Key, Mapped, Compare>::operator[](const key_type& key)
-> mapped_type& {
iterator found = tree::lower_bound(key);
if (found == tree::end() || tree::key_comp()(key, found->first))
found = tree::unsafe_emplace(found, key, mapped_type());
return found->second;
}
template <class Key, class Mapped, class Compare>
auto flat_map<Key, Mapped, Compare>::operator[](key_type&& key)
-> mapped_type& {
iterator found = tree::lower_bound(key);
if (found == tree::end() || tree::key_comp()(key, found->first))
found = tree::unsafe_emplace(found, std::move(key), mapped_type());
return found->second;
}
template <class Key, class Mapped, class Compare>
template <class K, class M>
auto flat_map<Key, Mapped, Compare>::insert_or_assign(K&& key, M&& obj)
-> std::pair<iterator, bool> {
auto result =
tree::emplace_key_args(key, std::forward<K>(key), std::forward<M>(obj));
if (!result.second)
result.first->second = std::forward<M>(obj);
return result;
}
template <class Key, class Mapped, class Compare>
template <class K, class M>
auto flat_map<Key, Mapped, Compare>::insert_or_assign(const_iterator hint,
K&& key,
M&& obj) -> iterator {
auto result = tree::emplace_hint_key_args(hint, key, std::forward<K>(key),
std::forward<M>(obj));
if (!result.second)
result.first->second = std::forward<M>(obj);
return result.first;
}
template <class Key, class Mapped, class Compare>
template <class K, class... Args>
auto flat_map<Key, Mapped, Compare>::try_emplace(K&& key, Args&&... args)
-> std::enable_if_t<std::is_constructible<key_type, K&&>::value,
std::pair<iterator, bool>> {
return tree::emplace_key_args(
key, std::piecewise_construct,
std::forward_as_tuple(std::forward<K>(key)),
std::forward_as_tuple(std::forward<Args>(args)...));
}
template <class Key, class Mapped, class Compare>
template <class K, class... Args>
auto flat_map<Key, Mapped, Compare>::try_emplace(const_iterator hint,
K&& key,
Args&&... args)
-> std::enable_if_t<std::is_constructible<key_type, K&&>::value, iterator> {
return tree::emplace_hint_key_args(
hint, key, std::piecewise_construct,
std::forward_as_tuple(std::forward<K>(key)),
std::forward_as_tuple(std::forward<Args>(args)...))
.first;
}
// ----------------------------------------------------------------------------
// General operations.
template <class Key, class Mapped, class Compare>
void flat_map<Key, Mapped, Compare>::swap(flat_map& other) noexcept {
tree::swap(other);
}
} // namespace base
#endif // BASE_CONTAINERS_FLAT_MAP_H_