linked_hash_map.h
#ifndef LINKED_HASH_MAP_H_
#define LINKED_HASH_MAP_H_
#include <unordered_map>
#include <list>
#include "basic_macro.h"
#include "logging.h"
// This holds a list of pair<Key, Value> items. This list is what gets
// traversed, and it's iterators from this list that we return from
// begin/end/find.
//
// We also keep a map<Key, list::iterator> for find. Since std::list is a
// doubly-linked list, the iterators should remain stable.
template <class Key, class Value, class Hash = std::hash<Key>>
class linked_hash_map
{
private:
typedef std::list<std::pair<Key, Value>> ListType;
typedef std::unordered_map<Key, typename ListType::iterator, Hash> MapType;
public:
typedef typename ListType::iterator iterator;
typedef typename ListType::reverse_iterator reverse_iterator;
typedef typename ListType::const_iterator const_iterator;
typedef typename ListType::const_reverse_iterator const_reverse_iterator;
typedef typename MapType::key_type key_type;
typedef typename ListType::value_type value_type;
typedef typename ListType::size_type size_type;
linked_hash_map() = default;
explicit linked_hash_map(size_type bucket_count) : map_(bucket_count) {}
linked_hash_map(linked_hash_map &&other) = default;
linked_hash_map &operator=(linked_hash_map &&other) = default;
// Returns an iterator to the first (insertion-ordered) element. Like a map,
// this can be dereferenced to a pair<Key, Value>.
iterator begin()
{
return list_.begin();
}
const_iterator begin() const
{
return list_.begin();
}
// Returns an iterator beyond the last element.
iterator end()
{
return list_.end();
}
const_iterator end() const
{
return list_.end();
}
// Returns an iterator to the last (insertion-ordered) element. Like a map,
// this can be dereferenced to a pair<Key, Value>.
reverse_iterator rbegin()
{
return list_.rbegin();
}
const_reverse_iterator rbegin() const
{
return list_.rbegin();
}
// Returns an iterator beyond the first element.
reverse_iterator rend()
{
return list_.rend();
}
const_reverse_iterator rend() const
{
return list_.rend();
}
// Front and back accessors common to many stl containers.
// Returns the earliest-inserted element
const value_type &front() const
{
return list_.front();
}
// Returns the earliest-inserted element.
value_type &front()
{
return list_.front();
}
// Returns the most-recently-inserted element.
const value_type &back() const
{
return list_.back();
}
// Returns the most-recently-inserted element.
value_type &back()
{
return list_.back();
}
// Clears the map of all values.
void clear()
{
map_.clear();
list_.clear();
}
// Returns true iff the map is empty.
bool empty() const
{
return list_.empty();
}
// Removes the first element from the list.
void pop_front() { erase(begin()); }
// Erases values with the provided key. Returns the number of elements
// erased. In this implementation, this will be 0 or 1.
size_type erase(const Key &key)
{
typename MapType::iterator found = map_.find(key);
if (found == map_.end())
return 0;
list_.erase(found->second);
map_.erase(found);
return 1;
}
// Erases the item that 'position' points to. Returns an iterator that points
// to the item that comes immediately after the deleted item in the list, or
// end().
// If the provided iterator is invalid or there is inconsistency between the
// map and list, a CHECK() error will occur.
iterator erase(iterator position)
{
typename MapType::iterator found = map_.find(position->first);
if(found->second != position){
DLOG(FATAL)<<"Inconsisent iterator for map and list, or the iterator is invalid.";
}
map_.erase(found);
return list_.erase(position);
}
// Erases all the items in the range [first, last). Returns an iterator that
// points to the item that comes immediately after the last deleted item in
// the list, or end().
iterator erase(iterator first, iterator last)
{
while (first != last && first != end())
{
first = erase(first);
}
return first;
}
// Finds the element with the given key. Returns an iterator to the
// value found, or to end() if the value was not found. Like a map, this
// iterator points to a pair<Key, Value>.
iterator find(const Key &key)
{
typename MapType::iterator found = map_.find(key);
if (found == map_.end())
{
return end();
}
return found->second;
}
const_iterator find(const Key &key) const
{
typename MapType::const_iterator found = map_.find(key);
if (found == map_.end())
{
return end();
}
return found->second;
}
// Returns the bounds of a range that includes all the elements in the
// container with a key that compares equal to x.
std::pair<iterator, iterator> equal_range(const key_type &key)
{
std::pair<typename MapType::iterator, typename MapType::iterator> eq_range =
map_.equal_range(key);
return std::make_pair(eq_range.first->second, eq_range.second->second);
}
std::pair<const_iterator, const_iterator> equal_range(
const key_type &key) const
{
std::pair<typename MapType::const_iterator,
typename MapType::const_iterator>
eq_range =
map_.equal_range(key);
const const_iterator &start_iter = eq_range.first != map_.end() ? eq_range.first->second : end();
const const_iterator &end_iter = eq_range.second != map_.end() ? eq_range.second->second : end();
return std::make_pair(start_iter, end_iter);
}
// Returns the value mapped to key, or an inserted iterator to that position
// in the map.
Value &operator[](const key_type &key)
{
return (*((this->insert(std::make_pair(key, Value()))).first)).second;
}
// Inserts an element into the map
std::pair<iterator, bool> insert(const std::pair<Key, Value> &pair)
{
// First make sure the map doesn't have a key with this value. If it does,
// return a pair with an iterator to it, and false indicating that we
// didn't insert anything.
typename MapType::iterator found = map_.find(pair.first);
if (found != map_.end())
return std::make_pair(found->second, false);
// Otherwise, insert into the list first.
list_.push_back(pair);
// Obtain an iterator to the newly added element. We do -- instead of -
// since list::iterator doesn't implement operator-().
typename ListType::iterator last = list_.end();
--last;
map_.insert(std::make_pair(pair.first, last));
return std::make_pair(last, true);
}
size_type size() const
{
return list_.size();
}
template <typename... Args>
std::pair<iterator, bool> emplace(Args &&... args)
{
ListType node_donor;
auto node_pos =
node_donor.emplace(node_donor.end(), std::forward<Args>(args)...);
const auto &k = node_pos->first;
auto ins = map_.insert({k, node_pos});
if (!ins.second)
return {ins.first->second, false};
list_.splice(list_.end(), node_donor, node_pos);
return {ins.first->second, true};
}
void swap(linked_hash_map &other)
{
map_.swap(other.map_);
list_.swap(other.list_);
}
private:
// The map component, used for speedy lookups
MapType map_;
// The list component, used for maintaining insertion order
ListType list_;
// |map_| contains iterators to |list_|, therefore a default copy constructor
// or copy assignment operator would result in an inconsistent state.
DISALLOW_COPY_AND_ASSIGN(linked_hash_map);
};
#endif
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