pilotclient/src/misc/memotable.h

// SPDX-FileCopyrightText: Copyright (C) 2016 swift Project Community / Contributors
// SPDX-License-Identifier: GPL-3.0-or-later OR LicenseRef-swift-pilot-client-1

//! \file

#ifndef SWIFT_MISC_MEMOTABLE_H
#define SWIFT_MISC_MEMOTABLE_H

#include "misc/dictionary.h"
#include "misc/sequence.h"

namespace swift::misc
{
    /*!
     * A data memoization pattern useful for compressing JSON representations of containers.
     */
    template <typename T>
    class CMemoTable
    {
    public:
        //! Return the index of a value, inserting it if it is not already in the table.
        int getIndex(const T &value)
        {
            int &index = m_dict[value];
            if (!index)
            {
                m_list.push_back(value);
                index = m_list.size();
            }
            return index - 1;
        }

        //! Return the values in the table as a flat list.
        const CSequence<T> &getTable() const { return m_list; }

    private:
        CSequence<T> m_list;
        CDictionary<T, int, QMap> m_dict;
    };

    /*!
     * Helper class for memoizing members of a value object.
     */
    template <typename... Ts>
    struct CMemoHelper
    {
        //! Memoizer for Ts. Other types are passed through.
        class CMemoizer : private CMemoTable<Ts>...
        {
        public:
            //! If T is in Ts, return the index of member in the memo table. Otherwise, return member.
            template <typename T>
            decltype(auto) maybeMemoize(const T &member)
            {
                if constexpr ((std::is_same_v<T, Ts> || ...)) { return this->CMemoTable<T>::getIndex(member); }
                else { return std::as_const(member); }
            }

            //! Return the values in the T table as a flat list.
            template <typename T>
            const CSequence<T> &getTable() const
            {
                return this->CMemoTable<T>::getTable();
            }
        };

        //! Unmemoizer for Ts. Other types are passed through.
        class CUnmemoizer : private CSequence<Ts>...
        {
        public:
            //! Return reference to the flat list T table.
            template <typename T>
            CSequence<T> &getTable()
            {
                return *this;
            }

            //! If T is in Ts, return proxy that will assign to member through the value at the given index in the flat
            //! list. Otherwise, return member as std::reference_wrapper.
            template <typename T>
            auto maybeUnmemoize(T &member) const
            {
                if constexpr ((std::is_same_v<T, Ts> || ...))
                {
                    struct Memo // clazy:exclude=rule-of-three
                    {
                        int index;
                        T &member;
                        const CSequence<T> &list;
                        int &get() { return index; }
                        ~Memo()
                        {
                            if (index >= 0) { member = list[index]; }
                        }
                    };
                    return Memo { -1, member, static_cast<const CSequence<T> &>(*this) };
                }
                else { return std::ref(member); }
            }
        };
    };
} // namespace swift::misc

#endif