StackHashMap.h

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/*
 * MIT License
 *
 * Copyright (c) 2026 nfx
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
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 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
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 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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 * SOFTWARE.
 */

 
#pragma once
 
#include "nfx/containers/FastHashMap.h"
 
#include <array>
#include <cstddef>
#include <functional>
#include <initializer_list>
#include <memory>
#include <optional>
#include <utility>
 
namespace nfx::containers
{
    //=====================================================================
    // StackHashMap class
    //=====================================================================

    template <typename TKey,
        typename TValue,
        size_t N = 8,
        typename KeyEqual = std::equal_to<>>
    class StackHashMap final
    {
    public:
        //----------------------------------------------
        // STL-compatible type aliases
        //----------------------------------------------

        using key_type = TKey;

        using mapped_type = TValue;

        using value_type = std::pair<const TKey, TValue>;

        using size_type = size_t;

        using difference_type = std::ptrdiff_t;

        using key_equal = KeyEqual;
 
        //----------------------------------------------
        // Construction
        //----------------------------------------------

        inline StackHashMap();

        inline StackHashMap( std::initializer_list<std::pair<TKey, TValue>> init );

        template <typename InputIt>
        inline StackHashMap( InputIt first, InputIt last );
 
        //----------------------------------------------
        // Capacity
        //----------------------------------------------

        [[nodiscard]] inline bool isEmpty() const noexcept;

        [[nodiscard]] inline size_t size() const noexcept;

        [[nodiscard]] static constexpr size_t stackCapacity() noexcept { return N; }
 
        //----------------------------------------------
        // Element access
        //----------------------------------------------

        inline TValue& at( const TKey& key );

        inline const TValue& at( const TKey& key ) const;

        inline TValue& operator[]( const TKey& key );

        inline TValue& operator[]( TKey&& key );
 
        //----------------------------------------------
        // Modifiers
        //----------------------------------------------

        inline std::pair<value_type*, bool> insert( const std::pair<TKey, TValue>& value );

        inline std::pair<value_type*, bool> insert( std::pair<TKey, TValue>&& value );

        template <typename... Args>
        inline std::pair<value_type*, bool> emplace( Args&&... args );

        inline void insertOrAssign( const TKey& key, const TValue& value );

        inline void insertOrAssign( const TKey& key, TValue&& value );

        inline void insertOrAssign( TKey&& key, TValue&& value );

        inline size_t erase( const TKey& key );

        inline void clear() noexcept;

        [[nodiscard]] inline std::optional<std::pair<TKey, TValue>> extract( const TKey& key );

        inline void merge( StackHashMap& other );

        inline void merge( StackHashMap&& other );
 
        //----------------------------------------------
        // Lookup
        //----------------------------------------------

        [[nodiscard]] inline TValue* find( const TKey& key ) noexcept;

        [[nodiscard]] inline const TValue* find( const TKey& key ) const noexcept;

        [[nodiscard]] inline size_t count( const TKey& key ) const;

        [[nodiscard]] inline bool contains( const TKey& key ) const;

        template <typename K>
        [[nodiscard]] inline bool contains( const K& key ) const
            requires requires( KeyEqual eq, const K& k, const TKey& t ) { eq( k, t ); };
 
        //----------------------------------------------
        // Iteration
        //----------------------------------------------

        template <typename Func>
        inline void forEach( Func&& func );

        template <typename Func>
        inline void forEach( Func&& func ) const;
 
    private:
        //----------------------------------------------
        // Internal storage
        //----------------------------------------------

        struct StackEntry
        {
            std::optional<std::pair<TKey, TValue>> data; 
        };

        std::array<StackEntry, N> m_stack;

        size_t m_stackSize;

        std::unique_ptr<FastHashMap<TKey, TValue>> m_heap;

        [[nodiscard]] inline bool isOnStack() const noexcept;

        inline void transitionToHeap();
    };
} // namespace nfx::containers
 
#include "nfx/detail/containers/StackHashMap.inl"