home/src/interned_string.hh

#ifndef interned_string_hh_INCLUDED
#define interned_string_hh_INCLUDED

#include "string.hh"
#include "utils.hh"

#include <unordered_map>

namespace Kakoune
{

class InternedString;

class StringRegistry : public Singleton<StringRegistry>
{
private:
    friend class InternedString;

    InternedString acquire(StringView str);
    void acquire(size_t slot);
    void release(size_t slot) noexcept;

    std::unordered_map<StringView, size_t> m_slot_map;
    std::vector<size_t> m_free_slots;
    using DataAndRefCount = std::pair<std::vector<char>, int>;
    std::vector<DataAndRefCount> m_storage;
};

class InternedString : public StringView
{
public:
    InternedString() = default;

    InternedString(const InternedString& str) : InternedString(str, str.m_slot)
    {
        if (m_slot != -1)
            StringRegistry::instance().acquire(m_slot);
    }

    InternedString(InternedString&& str) noexcept : StringView(str)
    {
        m_slot = str.m_slot;
        str.m_slot = -1;
    }

    InternedString(const char* str) : StringView() { acquire_ifn(str); }
    InternedString(StringView str) : StringView() { acquire_ifn(str); }

    InternedString& operator=(const InternedString& str)
    {
        if (str.data() == data() and str.length() == length())
            return *this;
        static_cast<StringView&>(*this) = str;
        if (str.m_slot != m_slot)
        {
            release_ifn();
            m_slot = str.m_slot;
            if (str.m_slot != -1)
                StringRegistry::instance().acquire(str.m_slot);
        }

        return *this;
    }

    InternedString& operator=(InternedString&& str) noexcept
    {
        release_ifn();

        static_cast<StringView&>(*this) = str;
        m_slot = str.m_slot;
        str.m_slot = -1;
        return *this;
    }

    ~InternedString()
    {
        release_ifn();
    }

    InternedString acquire_substr(ByteCount from, ByteCount length = INT_MAX) const
    {
        if (m_slot == -1)
            return InternedString{};
        StringRegistry::instance().acquire(m_slot);
        return InternedString{StringView::substr(from, length), m_slot};
    }
    InternedString acquire_substr(CharCount from, CharCount length = INT_MAX) const
    {
        if (m_slot == -1)
            return InternedString{};
        StringRegistry::instance().acquire(m_slot);
        return InternedString{StringView::substr(from, length), m_slot};
    }

private:
    friend class StringRegistry;

    InternedString(StringView str, size_t slot)
        : StringView(str), m_slot(slot) {}

    void acquire_ifn(StringView str)
    {
        if (str.empty())
        {
            static_cast<StringView&>(*this) = StringView{};
            m_slot = -1;
        }
        else
            *this = StringRegistry::instance().acquire(str);
    }

    void release_ifn() noexcept
    {
        if (m_slot != -1)
            StringRegistry::instance().release(m_slot);
    }

    size_t m_slot = -1;
};

}

namespace std
{
    template<>
    struct hash<Kakoune::InternedString>
    {
        size_t operator()(const Kakoune::InternedString& str) const
        {
            return Kakoune::hash_data(str.data(), (int)str.length());
        }
    };
}

#endif // interned_string_hh_INCLUDED