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/*
* Copyright (C) 2024 Apple Inc. All Rights Reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
* OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#pragma once
#include <variant>
#include <wtf/HashMap.h>
#include <wtf/ScopedLambda.h>
#include <wtf/StdLibExtras.h>
namespace WTF {
// This is a map optimized for holding 0 or 1 items with no hashing or allocations in those cases.
template<typename Key, typename Value>
class SmallMap {
public:
using Pair = KeyValuePair<Key, Value>;
using Map = UncheckedKeyHashMap<Key, Value>;
using Storage = std::variant<std::monostate, Pair, Map>;
static_assert(sizeof(Pair) <= 4 * sizeof(uint64_t), "Don't use SmallMap with large types. It probably wastes memory.");
Value& ensure(const Key& key, const auto& functor)
{
ASSERT(Map::isValidKey(key));
if (std::holds_alternative<std::monostate>(m_storage)) {
m_storage = Pair { key, functor() };
return std::get<Pair>(m_storage).value;
}
if (auto* pair = std::get_if<Pair>(&m_storage)) {
if (pair->key == key)
return pair->value;
Map map;
map.add(WTFMove(pair->key), WTFMove(pair->value));
m_storage = WTFMove(map);
return std::get<Map>(m_storage).add(key, functor()).iterator->value;
}
return std::get<Map>(m_storage).ensure(key, functor).iterator->value;
}
void remove(const Key& key)
{
ASSERT(Map::isValidKey(key));
if (auto* pair = std::get_if<Pair>(&m_storage)) {
if (pair->key == key)
m_storage = std::monostate { };
} else if (auto* map = std::get_if<Map>(&m_storage))
map->remove(key);
}
const Value* get(const Key& key) const
{
ASSERT(Map::isValidKey(key));
if (auto* pair = std::get_if<Pair>(&m_storage)) {
if (pair->key == key)
return std::addressof(pair->value);
} else if (auto* map = std::get_if<Map>(&m_storage)) {
if (auto it = map->find(key); it != map->end())
return std::addressof(it->value);
}
return nullptr;
}
void forEach(const auto& callback) const
{
switchOn(m_storage, [&] (const std::monostate&) {
}, [&] (const Pair& pair) {
callback(pair.key, pair.value);
}, [&] (const Map& map) {
for (auto& [key, value] : map)
callback(key, value);
});
}
size_t size() const
{
return switchOn(m_storage, [&] (const std::monostate&) {
return 0u;
}, [&] (const Pair&) {
return 1u;
}, [&] (const Map& map) {
return map.size();
});
}
const Storage& rawStorage() const { return m_storage; }
private:
Storage m_storage;
};
} // namespace WTF
using WTF::SmallMap;
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