StackHashSet.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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 */

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

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

        using key_type = TKey;

        using value_type = TKey;

        using size_type = size_t;

        using difference_type = std::ptrdiff_t;

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

        inline StackHashSet();

        inline StackHashSet( std::initializer_list<TKey> init );

        template <typename InputIt>
        inline StackHashSet( 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; }
 
        //----------------------------------------------
        // Modifiers
        //----------------------------------------------

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

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

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

        inline size_t erase( const TKey& key );

        inline void clear() noexcept;

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

        inline void merge( StackHashSet& other );

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

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

        [[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 ); };

        inline const TKey& at( const TKey& key ) const;
 
        //----------------------------------------------
        // 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<TKey> data; 
        };

        std::array<StackEntry, N> m_stack;

        size_t m_stackSize;

        std::unique_ptr<FastHashSet<TKey>> m_heap;

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

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