Source/WTF/wtf/WeakHashCountedSet.h

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#pragma once

#include <wtf/WeakHashMap.h>

namespace WTF {

template<typename Value, typename Counter = EmptyCounter>
class WeakHashCountedSet {
    WTF_MAKE_FAST_ALLOCATED;
private:
    using ImplType = WeakHashMap<Value, unsigned, Counter>;
public:
    using ValueType = Value;
    using iterator = typename ImplType::iterator;
    using const_iterator = typename ImplType::const_iterator;
    using AddResult = typename ImplType::AddResult;

    // Iterators iterate over pairs of values and counts.
    iterator begin() { return m_impl.begin(); }
    iterator end() { return m_impl.end(); }
    const_iterator begin() const { return m_impl.begin(); }
    const_iterator end() const { return m_impl.end(); }

    iterator find(const ValueType& value) { return m_impl.find(value); }
    const_iterator find(const ValueType& value) const { return m_impl.find(value); }
    bool contains(const ValueType& value) const { return m_impl.contains(value); }

    unsigned computeSize() const { return m_impl.computeSize(); }

    // Increments the count if an equal value is already present.
    // The return value includes both an iterator to the value's location,
    // and an isNewEntry bool that indicates whether it is a new or existing entry.
    AddResult add(const ValueType&);
    AddResult add(ValueType&&);

    // Decrements the count of the value, and removes it if count goes down to zero.
    // Returns true if the value is removed.
    bool remove(const ValueType&);
    bool remove(iterator);

    // Clears the whole set.
    void clear() { m_impl.clear(); }

private:
    WeakHashMap<Value, unsigned, Counter> m_impl;
};

template<typename Value, typename Counter>
inline auto WeakHashCountedSet<Value, Counter>::add(const ValueType &value) -> AddResult
{
    auto result = m_impl.add(value, 0);
    ++result.iterator->value;
    return result;
}

template<typename Value, typename Counter>
inline auto WeakHashCountedSet<Value, Counter>::add(ValueType&& value) -> AddResult
{
    auto result = m_impl.add(std::forward<Value>(value), 0);
    ++result.iterator->value;
    return result;
}

template<typename Value, typename Counter>
inline bool WeakHashCountedSet<Value, Counter>::remove(const ValueType& value)
{
    return remove(find(value));
}

template<typename Value, typename Counter>
inline bool WeakHashCountedSet<Value, Counter>::remove(iterator it)
{
    if (it == end())
        return false;

    unsigned oldVal = it->value;
    ASSERT(oldVal);
    unsigned newVal = oldVal - 1;
    if (newVal) {
        it->value = newVal;
        return false;
    }

    m_impl.remove(it);
    return true;
}

} // namespace WTF

using WTF::WeakHashCountedSet;