Mapping.inl

/*
 * Copyright(c) Sophist Solutions, Inc. 1990-2026.  All rights reserved
 */
 
/*
 ********************************************************************************
 ***************************** Implementation Details ***************************
 ********************************************************************************
 */
#include "Stroika/Foundation/Containers/Factory/Mapping_Factory.h"
#include "Stroika/Foundation/Debug/Assertions.h"
#include "Stroika/Foundation/Debug/Cast.h"
#include "Stroika/Foundation/Traversal/Generator.h"
 
namespace Stroika::Foundation::Containers {
 
    /*
     ********************************************************************************
     ******************** Mapping<KEY_TYPE, MAPPED_VALUE_TYPE> **********************
     ********************************************************************************
     */
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    inline Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::Mapping ()
        requires (IEqualsComparer<equal_to<KEY_TYPE>, KEY_TYPE>)
        : Mapping{equal_to<KEY_TYPE>{}}
    {
        _AssertRepValidType ();
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    template <IEqualsComparer<KEY_TYPE> KEY_EQUALS_COMPARER>
    inline Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::Mapping (KEY_EQUALS_COMPARER&& keyEqualsComparer)
        : inherited{Factory::Mapping_Factory<KEY_TYPE, MAPPED_VALUE_TYPE, remove_cvref_t<KEY_EQUALS_COMPARER>>::Default () (
              forward<KEY_EQUALS_COMPARER> (keyEqualsComparer))}
    {
        _AssertRepValidType ();
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    inline Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::Mapping (const initializer_list<KeyValuePair<KEY_TYPE, MAPPED_VALUE_TYPE>>& src)
        requires (IEqualsComparer<equal_to<KEY_TYPE>, KEY_TYPE>)
        : Mapping{}
    {
        AddAll (src);
        _AssertRepValidType ();
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    template <IEqualsComparer<KEY_TYPE> KEY_EQUALS_COMPARER>
    inline Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::Mapping (KEY_EQUALS_COMPARER&& keyEqualsComparer,
                                                          const initializer_list<KeyValuePair<KEY_TYPE, MAPPED_VALUE_TYPE>>& src)
        : Mapping{forward<KEY_EQUALS_COMPARER> (keyEqualsComparer)}
    {
        AddAll (src);
        _AssertRepValidType ();
    }
#if !qCompilerAndStdLib_RequiresNotMatchInlineOutOfLineForTemplateClassBeingDefined_Buggy
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    template <IIterableOfTo<KeyValuePair<KEY_TYPE, MAPPED_VALUE_TYPE>> ITERABLE_OF_ADDABLE>
    inline Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::Mapping (ITERABLE_OF_ADDABLE&& src)
        requires (IEqualsComparer<equal_to<KEY_TYPE>, KEY_TYPE> and
                  not derived_from<remove_cvref_t<ITERABLE_OF_ADDABLE>, Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>>)
        : Mapping{}
    {
        AddAll (forward<ITERABLE_OF_ADDABLE> (src));
        _AssertRepValidType ();
    }
#endif
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    template <IEqualsComparer<KEY_TYPE> KEY_EQUALS_COMPARER, IIterableOfTo<KeyValuePair<KEY_TYPE, MAPPED_VALUE_TYPE>> ITERABLE_OF_ADDABLE>
    inline Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::Mapping (KEY_EQUALS_COMPARER&& keyEqualsComparer, ITERABLE_OF_ADDABLE&& src)
        : Mapping{forward<KEY_EQUALS_COMPARER> (keyEqualsComparer)}
    {
        AddAll (forward<ITERABLE_OF_ADDABLE> (src));
        _AssertRepValidType ();
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    template <IInputIterator<KeyValuePair<KEY_TYPE, MAPPED_VALUE_TYPE>> ITERATOR_OF_ADDABLE, sentinel_for<remove_cvref_t<ITERATOR_OF_ADDABLE>> ITERATOR_OF_ADDABLE2>
    Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::Mapping (ITERATOR_OF_ADDABLE&& start, ITERATOR_OF_ADDABLE2&& end)
        requires (IEqualsComparer<equal_to<KEY_TYPE>, KEY_TYPE>)
        : Mapping{}
    {
        AddAll (forward<ITERATOR_OF_ADDABLE> (start), forward<ITERATOR_OF_ADDABLE2> (end));
        _AssertRepValidType ();
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    template <IEqualsComparer<KEY_TYPE> KEY_EQUALS_COMPARER, IInputIterator<KeyValuePair<KEY_TYPE, MAPPED_VALUE_TYPE>> ITERATOR_OF_ADDABLE,
              sentinel_for<remove_cvref_t<ITERATOR_OF_ADDABLE>> ITERATOR_OF_ADDABLE2>
    Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::Mapping (KEY_EQUALS_COMPARER&& keyEqualsComparer, ITERATOR_OF_ADDABLE&& start, ITERATOR_OF_ADDABLE2&& end)
        : Mapping{forward<KEY_EQUALS_COMPARER> (keyEqualsComparer)}
    {
        AddAll (forward<ITERATOR_OF_ADDABLE> (start), forward<ITERATOR_OF_ADDABLE2> (end));
        _AssertRepValidType ();
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    inline Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::Mapping (const shared_ptr<_IRep>& rep) noexcept
        : inherited{rep}
    {
        RequireNotNull (rep);
        _AssertRepValidType ();
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    inline Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::Mapping (shared_ptr<_IRep>&& rep) noexcept
        : inherited{(RequireExpression (rep != nullptr), move (rep))}
    {
        _AssertRepValidType ();
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    inline auto Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::GetKeyEqualsComparer () const -> KeyEqualsCompareFunctionType
    {
        return _SafeReadRepAccessor<_IRep>{this}._ConstGetRep ().GetKeyEqualsComparer ();
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    inline Iterable<KEY_TYPE> Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::Keys () const
    {
        return this->template Map<Iterable<KEY_TYPE>> ([] (const KeyValuePair<KEY_TYPE, MAPPED_VALUE_TYPE>& kvp) { return kvp.fKey; });
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    inline Iterable<MAPPED_VALUE_TYPE> Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::MappedValues () const
    {
        return this->template Map<Iterable<MAPPED_VALUE_TYPE>> (
            [] (const KeyValuePair<KEY_TYPE, MAPPED_VALUE_TYPE>& kvp) { return kvp.fValue; });
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    inline bool Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::Lookup (ArgByValueType<key_type> key, mapped_type* item) const
    {
        if (item == nullptr) {
            return _SafeReadRepAccessor<_IRep>{this}._ConstGetRep ().Lookup (key, nullptr);
        }
        else {
            optional<mapped_type> tmp;
            if (_SafeReadRepAccessor<_IRep>{this}._ConstGetRep ().Lookup (key, &tmp)) {
                *item = *tmp;
                return true;
            }
            return false;
        }
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    inline bool Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::Lookup (ArgByValueType<key_type> key, optional<mapped_type>* item) const
    {
        return _SafeReadRepAccessor<_IRep>{this}._ConstGetRep ().Lookup (key, item);
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    inline optional<MAPPED_VALUE_TYPE> Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::Lookup (ArgByValueType<key_type> key) const
    {
        optional<MAPPED_VALUE_TYPE> r;
        [[maybe_unused]] bool       result = _SafeReadRepAccessor<_IRep>{this}._ConstGetRep ().Lookup (key, &r);
        Ensure (result == r.has_value ());
        return r;
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    inline bool Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::Lookup (ArgByValueType<key_type> key, nullptr_t) const
    {
        return _SafeReadRepAccessor<_IRep>{this}._ConstGetRep ().Lookup (key, nullptr);
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    template <typename THROW_IF_MISSING>
    inline MAPPED_VALUE_TYPE Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::LookupChecked (ArgByValueType<key_type> key, const THROW_IF_MISSING& throwIfMissing) const
    {
        if (optional<MAPPED_VALUE_TYPE> r{Lookup (key)}) [[likely]] {
            return *r;
        }
        Execution::Throw (throwIfMissing);
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    inline MAPPED_VALUE_TYPE Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::LookupValue (ArgByValueType<key_type> key, ArgByValueType<mapped_type> defaultValue) const
    {
        optional<MAPPED_VALUE_TYPE> r{Lookup (key)};
        return r.has_value () ? *r : defaultValue;
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    inline auto Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::operator[] (ArgByValueType<key_type> key) const -> add_const_t<mapped_type>
    {
        return *Lookup (key);
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    inline bool Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::ContainsKey (ArgByValueType<key_type> key) const
    {
        return _SafeReadRepAccessor<_IRep>{this}._ConstGetRep ().Lookup (key, nullptr);
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    template <typename VALUE_EQUALS_COMPARER>
    inline bool Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::ContainsMappedValue (ArgByValueType<mapped_type> v, VALUE_EQUALS_COMPARER&& valueEqualsComparer) const
    {
        return this->Find ([&valueEqualsComparer, &v] (const auto& t) { return valueEqualsComparer (t.fValue, v); }) != nullptr;
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    inline bool Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::Add (ArgByValueType<key_type> key, ArgByValueType<mapped_type> newElt, AddReplaceMode addReplaceMode)
    {
        return _SafeReadWriteRepAccessor<_IRep>{this}._GetWriteableRep ().Add (key, newElt, addReplaceMode);
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    inline bool Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::Add (ArgByValueType<value_type> p, AddReplaceMode addReplaceMode)
    {
        return _SafeReadWriteRepAccessor<_IRep>{this}._GetWriteableRep ().Add (p.fKey, p.fValue, addReplaceMode);
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    template <IInputIterator<KeyValuePair<KEY_TYPE, MAPPED_VALUE_TYPE>> ITERATOR_OF_ADDABLE, sentinel_for<remove_cvref_t<ITERATOR_OF_ADDABLE>> ITERATOR_OF_ADDABLE2>
    unsigned int Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::AddAll (ITERATOR_OF_ADDABLE&& start, ITERATOR_OF_ADDABLE2&& end, AddReplaceMode addReplaceMode)
    {
        unsigned int cntAdded{};
        for (auto i = forward<ITERATOR_OF_ADDABLE> (start); i != forward<ITERATOR_OF_ADDABLE2> (end); ++i) {
            if (Add (*i, addReplaceMode)) {
                ++cntAdded;
            }
        }
        return cntAdded;
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    template <IIterableOfTo<KeyValuePair<KEY_TYPE, MAPPED_VALUE_TYPE>> ITERABLE_OF_ADDABLE>
    inline unsigned int Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::AddAll (ITERABLE_OF_ADDABLE&& items, AddReplaceMode addReplaceMode)
    {
        if constexpr (std::is_convertible_v<remove_cvref_t<ITERABLE_OF_ADDABLE>*, Iterable<value_type>*>) {
            // very rare corner case
            if (static_cast<const Iterable<value_type>*> (this) == static_cast<const Iterable<value_type>*> (&items)) [[unlikely]] {
                vector<value_type> copy{std::begin (items), Iterator<value_type>{std::end (items)}}; // because you can not iterate over a container while modifying it
                return AddAll (std::begin (copy), std::end (copy), addReplaceMode);
            }
        }
        return AddAll (std::begin (items), std::end (items), addReplaceMode);
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    inline void Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::Remove (ArgByValueType<key_type> key)
    {
        Verify (_SafeReadWriteRepAccessor<_IRep>{this}._GetWriteableRep ().RemoveIf (key)); // use RemoveIf () if key may not exist
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    inline void Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::Remove (const Iterator<value_type>& i, Iterator<value_type>* nextI)
    {
        Require (not i.AtEnd ());
        auto [writerRep, patchedIterator] = _GetWritableRepAndPatchAssociatedIterator (i);
        writerRep->Remove (patchedIterator, nextI);
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    inline bool Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::RemoveIf (ArgByValueType<key_type> key)
    {
        return _SafeReadWriteRepAccessor<_IRep>{this}._GetWriteableRep ().RemoveIf (key);
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    inline void Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::RemoveAll ()
    {
        _SafeReadRepAccessor<_IRep> accessor{this}; // important to use READ not WRITE accessor, because write accessor would have already cloned the data
        if (not accessor._ConstGetRep ().empty ()) {
            this->_fRep = accessor._ConstGetRep ().CloneEmpty ();
        }
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    template <typename ITERABLE_OF_KEY_OR_ADDABLE>
    size_t Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::RemoveAll (const ITERABLE_OF_KEY_OR_ADDABLE& items)
        requires (IIterableOfTo<ITERABLE_OF_KEY_OR_ADDABLE, KeyValuePair<KEY_TYPE, MAPPED_VALUE_TYPE>> or
                  IIterableOfTo<ITERABLE_OF_KEY_OR_ADDABLE, pair<KEY_TYPE, MAPPED_VALUE_TYPE>> or IIterableOfTo<ITERABLE_OF_KEY_OR_ADDABLE, KEY_TYPE>)
    {
        using ITEM_T = ranges::range_value_t<ITERABLE_OF_KEY_OR_ADDABLE>;
        static_assert (is_convertible_v<ITEM_T, key_type> or is_convertible_v<ITEM_T, pair<key_type, mapped_type>> or
                       is_convertible_v<ITEM_T, KeyValuePair<key_type, mapped_type>>);
        if constexpr (convertible_to<const Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>*, const ITERABLE_OF_KEY_OR_ADDABLE*>) {
            if (this == &items) { // avoid modifying container while iterating over it
                size_t result = this->size ();
                RemoveAll ();
                return result;
            }
        }
        return this->RemoveAll (begin (items), end (items));
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    template <typename ITERATOR_OF_KEY_OR_ADDABLE, sentinel_for<remove_cvref_t<ITERATOR_OF_KEY_OR_ADDABLE>> ITERATOR_OF_KEY_OR_ADDABLE2>
    inline size_t Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::RemoveAll (ITERATOR_OF_KEY_OR_ADDABLE&& start, ITERATOR_OF_KEY_OR_ADDABLE2&& end)
    {
        using ITEM_T = iter_value_t<ITERATOR_OF_KEY_OR_ADDABLE>;
        static_assert (is_convertible_v<ITEM_T, key_type> or is_convertible_v<ITEM_T, pair<key_type, mapped_type>> or
                       is_convertible_v<ITEM_T, KeyValuePair<key_type, mapped_type>>);
        size_t cnt{};
        for (auto i = start; i != end; ++i) {
            if constexpr (is_convertible_v<ITEM_T, key_type>) {
                if (RemoveIf (*i)) {
                    ++cnt;
                }
            }
            else if constexpr (is_convertible_v<ITEM_T, pair<key_type, mapped_type>>) {
                if (RemoveIf (i->first)) {
                    ++cnt;
                }
            }
            else if constexpr (is_convertible_v<ITEM_T, KeyValuePair<key_type, mapped_type>>) {
                if (RemoveIf (i->fKey)) {
                    ++cnt;
                }
            }
            else {
                AssertNotReached ();
            }
        }
        return cnt;
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    template <predicate<KeyValuePair<KEY_TYPE, MAPPED_VALUE_TYPE>> PREDICATE>
    size_t Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::RemoveAll (PREDICATE&& p)
    {
        size_t nRemoved{};
        for (Iterator<KeyValuePair<KEY_TYPE, MAPPED_VALUE_TYPE>> i = this->begin (); i != this->end ();) {
            if (p (*i)) {
                Remove (i, &i);
                ++nRemoved;
            }
            else {
                ++i;
            }
        }
        return nRemoved;
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    inline void Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::Update (const Iterator<value_type>& i, ArgByValueType<mapped_type> newValue,
                                                              Iterator<value_type>* nextI)
    {
        Require (not i.AtEnd ());
        auto [writerRep, patchedIterator] = _GetWritableRepAndPatchAssociatedIterator (i);
        writerRep->Update (patchedIterator, newValue, nextI);
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    template <IIterableOfTo<KEY_TYPE> ITERABLE_OF_KEY_TYPE>
    void Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::RetainAll (const ITERABLE_OF_KEY_TYPE& items)
    {
        /*
         *  If items is smaller than this->size(), probably best to just remove one or two things from this 
         *  (small number of lookups, and maybe no changes).
         * 
         *  If items is large, probably best to just create the entire mapping anew (cuz probably
         *  producing much smaller map).
         * 
         *  And both approaches avoid needing to quickly search through items repeatedly (except
         *  when we know items is small so no cost).
         * 
         *  NOT too worried about optimizing this code - but really quite unsure about this analysis of which way is faster.
         *      --LGP 2025-04-01
         */
        size_t thisSize = this->size ();
 
        // Small case - just remove a few items
        bool fewerLookupsThanAdds = items.size () <= 2;
        if (fewerLookupsThanAdds) {
            // Algorithm COMP COMPLEXITY VERY ROUHLTY apx= (O(Items-N) * O(THIS_LEN-N)) bad estimate cuz ignores cost of erases
            auto keyEqualsComparer = this->GetKeyEqualsComparer ();
            using ITEMS_ITER_TYPE = decltype (items.begin ()); // because of new ranges (c++20) code - sentinel but find_if only templated on one iter parameter
            for (Iterator<value_type> i = this->begin (); i != this->end ();) {
                if (find_if<ITEMS_ITER_TYPE> (items.begin (), items.end (),
                                              [&] (const KEY_TYPE& k) { return keyEqualsComparer (i->fKey, k); }) == items.end ()) {
#if qStroika_Foundation_Debug_AssertionsChecked
                    [[maybe_unused]] size_t sz = this->size ();
#endif
                    i = this->erase (i);
#if qStroika_Foundation_Debug_AssertionsChecked
                    Assert (this->size () == sz - 1u);
#endif
                }
                else {
                    ++i;
                }
            }
        }
        else {
            // Algorithm COMP COMPLEXITY apx= O(Items-N) * O(LOG(THIS_LEN-N)) - assuming tree style org for map, or O(1) if hashtable - bad estimate ignores cost of adds
            // Fall thru, and just recreate the mapping
            Mapping result = Mapping{_SafeReadRepAccessor<_IRep>{this}._ConstGetRep ().CloneEmpty ()};
            size_t  nAdds{0};
            for (auto key2Keep : items) {
                if (auto l = this->Lookup (key2Keep)) {
                    result.Add (key2Keep, *l);
                    ++nAdds;
                }
            }
            // if nothing changed, we can just make no changes
            if (thisSize != nAdds) {
                *this = result;
            }
            else {
                if constexpr (equality_comparable<MAPPED_VALUE_TYPE>) {
                    Assert (*this == result); // so why assign?
                }
                else {
                    // @todo assert keys equal...
                }
            }
        }
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    template <typename RESULT_CONTAINER, invocable<KeyValuePair<KEY_TYPE, MAPPED_VALUE_TYPE>> ELEMENT_MAPPER>
    RESULT_CONTAINER Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::Map (ELEMENT_MAPPER&& elementMapper) const
        requires (convertible_to<invoke_result_t<ELEMENT_MAPPER, KeyValuePair<KEY_TYPE, MAPPED_VALUE_TYPE>>, typename RESULT_CONTAINER::value_type> or
                  convertible_to<invoke_result_t<ELEMENT_MAPPER, KeyValuePair<KEY_TYPE, MAPPED_VALUE_TYPE>>, optional<typename RESULT_CONTAINER::value_type>>)
    {
        if constexpr (same_as<RESULT_CONTAINER, Mapping>) {
            // clone the rep so we retain any ordering function/etc, rep type
            return inherited::template Map<RESULT_CONTAINER> (forward<ELEMENT_MAPPER> (elementMapper),
                                                              RESULT_CONTAINER{_SafeReadRepAccessor<_IRep>{this}._ConstGetRep ().CloneEmpty ()});
        }
        else {
            return inherited::template Map<RESULT_CONTAINER> (forward<ELEMENT_MAPPER> (elementMapper)); // default Iterable<> implementation then...
        }
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    template <derived_from<Iterable<KeyValuePair<KEY_TYPE, MAPPED_VALUE_TYPE>>> RESULT_CONTAINER, typename INCLUDE_PREDICATE>
    inline auto Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::Where (INCLUDE_PREDICATE&& includeIfTrue) const -> RESULT_CONTAINER
        requires (predicate<INCLUDE_PREDICATE, KEY_TYPE> or predicate<INCLUDE_PREDICATE, KeyValuePair<KEY_TYPE, MAPPED_VALUE_TYPE>>)
    {
        if constexpr (predicate<INCLUDE_PREDICATE, KEY_TYPE>) {
            // recurse once with a KVP predicate
            return Where<RESULT_CONTAINER> (
                [=] (const ArgByValueType<KeyValuePair<KEY_TYPE, MAPPED_VALUE_TYPE>>& kvp) { return includeIfTrue (kvp.fKey); });
        }
        else {
            if constexpr (same_as<RESULT_CONTAINER, Mapping>) {
                // clone the rep so we retain any ordering function/etc, rep type
                return inherited::template Where<RESULT_CONTAINER> (
                    forward<INCLUDE_PREDICATE> (includeIfTrue), RESULT_CONTAINER{_SafeReadRepAccessor<_IRep>{this}._ConstGetRep ().CloneEmpty ()});
            }
            else {
                return inherited::template Where<RESULT_CONTAINER> (forward<INCLUDE_PREDICATE> (includeIfTrue)); // default Iterable<> implementation then...
            }
        }
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    template <typename CONTAINER_OF_KEYS>
    inline auto Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::WithKeys (const CONTAINER_OF_KEYS& includeKeys) const -> ArchetypeContainerType
    {
        return Where ([=] (const key_type& key) -> bool { return includeKeys.Contains (key); });
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    inline auto Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::WithKeys (const initializer_list<key_type>& includeKeys) const -> ArchetypeContainerType
    {
        Iterable<key_type> ik{includeKeys};
        return inherited::Where ([=] (const ArgByValueType<value_type>& kvp) { return ik.Contains (kvp.fKey); }, ArchetypeContainerType{});
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    template <typename CONTAINER_OF_Key_T>
    inline CONTAINER_OF_Key_T Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::As () const
    {
        return As_<CONTAINER_OF_Key_T> ();
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    template <typename CONTAINER_OF_Key_T>
    CONTAINER_OF_Key_T Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::As_ () const
    {
        CONTAINER_OF_Key_T result;
        for (const auto& i : *this) {
            // the reason we use the overload with an extra result.end () here is so it will work with std::map<> or std::vector<>
            if constexpr (is_convertible_v<typename CONTAINER_OF_Key_T::value_type, pair<KEY_TYPE, MAPPED_VALUE_TYPE>>) {
                result.insert (result.end (), pair<KEY_TYPE, MAPPED_VALUE_TYPE>{i.fKey, i.fValue});
            }
            else {
                result.insert (result.end (), value_type{i.fKey, i.fValue});
            }
        }
        return result;
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    inline void Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::Accumulate (ArgByValueType<key_type> key, ArgByValueType<mapped_type> newValue,
                                                                  const function<mapped_type (ArgByValueType<mapped_type>, ArgByValueType<mapped_type>)>& f,
                                                                  mapped_type initialValue)
    {
        Add (key, f (LookupValue (key, initialValue), newValue));
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    inline void Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::insert (ArgByValueType<value_type> kvp)
    {
        Add (kvp.fKey, kvp.fValue);
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    inline void Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::erase (ArgByValueType<key_type> key)
    {
        Remove (key);
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    inline auto Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::erase (const Iterator<value_type>& i) -> Iterator<value_type>
    {
        Iterator<value_type> nextI{nullptr};
        Remove (i, &nextI);
        return nextI;
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    inline void Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::clear ()
    {
        RemoveAll ();
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    template <IIterableOfTo<KeyValuePair<KEY_TYPE, MAPPED_VALUE_TYPE>> ITERABLE_OF_ADDABLE>
    inline Mapping<KEY_TYPE, MAPPED_VALUE_TYPE> Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::operator+ (const ITERABLE_OF_ADDABLE& items) const
    {
        Mapping<KEY_TYPE, MAPPED_VALUE_TYPE> result = *this;
        result.AddAll (items);
        return result;
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    template <IIterableOfTo<KeyValuePair<KEY_TYPE, MAPPED_VALUE_TYPE>> ITERABLE_OF_ADDABLE>
    inline Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>& Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::operator+= (const ITERABLE_OF_ADDABLE& items)
    {
        AddAll (items);
        return *this;
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    template <typename ITERABLE_OF_KEY_OR_ADDABLE>
    inline Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>& Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::operator-= (const ITERABLE_OF_KEY_OR_ADDABLE& items)
    {
        RemoveAll (items);
        return *this;
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    auto Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::_GetWritableRepAndPatchAssociatedIterator (const Iterator<value_type>& i)
        -> tuple<_IRep*, Iterator<value_type>>
    {
        Require (not i.AtEnd ());
        using element_type                   = typename inherited::_SharedByValueRepType::element_type;
        Iterator<value_type> patchedIterator = i;
        element_type* writableRep = this->_fRep.rwget ([&] (const element_type& prevRepPtr) -> typename inherited::_SharedByValueRepType::shared_ptr_type {
            return Debug::UncheckedDynamicCast<const _IRep&> (prevRepPtr).CloneAndPatchIterator (&patchedIterator);
        });
        AssertNotNull (writableRep);
        return make_tuple (Debug::UncheckedDynamicCast<_IRep*> (writableRep), move (patchedIterator));
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    inline void Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::_AssertRepValidType () const
    {
        if constexpr (qStroika_Foundation_Debug_AssertionsChecked) {
            [[maybe_unused]] _SafeReadRepAccessor<_IRep> ignored{this};
        }
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    inline bool Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::operator== (const Mapping& rhs) const
        requires (equality_comparable<MAPPED_VALUE_TYPE>)
    {
        return EqualsComparer<>{}(*this, rhs);
    }
 
    /*
     ********************************************************************************
     ************ Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::EqualsComparer **************
     ********************************************************************************
     */
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    template <typename VALUE_EQUALS_COMPARER>
    constexpr Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::EqualsComparer<VALUE_EQUALS_COMPARER>::EqualsComparer (const VALUE_EQUALS_COMPARER& valueEqualsComparer)
        : fValueEqualsComparer{valueEqualsComparer}
    {
    }
    template <typename KEY_TYPE, typename MAPPED_VALUE_TYPE>
    template <typename VALUE_EQUALS_COMPARER>
    bool Mapping<KEY_TYPE, MAPPED_VALUE_TYPE>::EqualsComparer<VALUE_EQUALS_COMPARER>::operator() (const Mapping& lhs, const Mapping& rhs) const
    {
        /*
         *    @todo   THIS CODE IS TOO COMPLICATED, and COULD USE CLEANUP/CODE REVIEW - LGP 2014-06-11
         */
        _SafeReadRepAccessor<_IRep> lhsR{&lhs};
        _SafeReadRepAccessor<_IRep> rhsR{&rhs};
        if (&lhsR._ConstGetRep () == &rhsR._ConstGetRep ()) [[unlikely]] {
            // not such an unlikely test result since we use lazy copy, but this test is only an optimization and not logically required
            return true;
        }
        // Check length, so we don't need to check both iterators for end/done
        if (lhsR._ConstGetRep ().size () != rhsR._ConstGetRep ().size ()) [[likely]] {
            return false;
        }
        /*
         *  Two Mappings compare equal, if they have the same domain, and map each element of that domain to the same range.
         *  They need not be in the same order to compare equals. Still - they often are, and if they are, this algorithm is faster.
         *  If they miss, we need to fall back to a slower strategy.
         */
        auto li                = lhsR._ConstGetRep ().MakeIterator ();
        auto ri                = rhs.MakeIterator ();
        auto keyEqualsComparer = lhs.GetKeyEqualsComparer (); // arbitrarily select left side key equals comparer
        while (not li.AtEnd ()) {
            Assert (not ri.AtEnd ()); // cuz move at same time and same size
            bool keysEqual = keyEqualsComparer (li->fKey, ri->fKey);
            Require (keysEqual == rhs.GetKeyEqualsComparer () (li->fKey, ri->fKey)); // if fails, cuz rhs/lhs keys equals comparers disagree
            if (keysEqual) {
                // then we are doing in same order so can do quick impl
                if (not fValueEqualsComparer (li->fValue, ri->fValue)) {
                    return false;
                }
            }
            else {
                // check if li maps to right value in rhs
                auto o = rhs.Lookup (li->fKey);
                if (not o.has_value () or not fValueEqualsComparer (*o, li->fValue)) {
                    return false;
                }
                // if the keys were different, we must check the reverse direction too
                if (not lhsR._ConstGetRep ().Lookup (ri->fKey, &o) or not fValueEqualsComparer (*o, ri->fValue)) {
                    return false;
                }
            }
            // if we got this far, all compared OK so far, so keep going
            ++li;
            ++ri;
        }
        Assert (ri.AtEnd ()); // cuz LHS done and both sides iterate at same pace, and we checked both same size
        return true;
    }
 
}