HashBuilder.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "Concepts/GetTypeHashable.h"
#include "Containers/Map.h"
#include "Containers/UnrealString.h"
#include "Hash/CityHash.h"
 
class FHashBuilder
{
public:
    explicit FHashBuilder(uint32 InHash = 0)
        : Hash(~InHash)
    {}
 
    inline FHashBuilder& AppendRaw(const void* Data, int64 Num)
    {
        Hash = HashCombineFast(Hash, GetTypeHash(CityHash64(static_cast<const char*>(Data),  static_cast<int32>(Num))));
        return *this;
    }
 
    template <typename T>
    UE_FORCEINLINE_HINT typename TEnableIf<TIsPODType<T>::Value, FHashBuilder&>::Type AppendRaw(const T& InData)
    {
        return AppendRaw(&InData, sizeof(T));
    }
 
    template <typename T>
    inline FHashBuilder& Append(const T& InData)
    {
        if constexpr (TModels_V<CGetTypeHashable, T>)
        {
            Hash = HashCombineFast(Hash, GetTypeHash(InData));
            return *this;
        }
        else
        {
            return AppendRaw(InData);
        }
    }
 
    template <typename T>
    inline FHashBuilder& Append(const TArray<T>& InArray)
    {
        for (const T& Value: InArray)
        {
            Append(Value);
        }
        return *this;
    }
 
    template <typename T>
    inline FHashBuilder& Append(const TSet<T>& InSet)
    {
        for (const T& Value: InSet)
        {
            Append(Value);
        }
        return *this;
    }
 
    template <typename T, typename U>
    inline FHashBuilder& Append(const TMap<T, U>& InMap)
    {
        for (const TPair<T, U>& Value: InMap)
        {
            Append(Value.Key);
            Append(Value.Value);
        }
        return *this;
    }
 
    template <typename T>
    UE_FORCEINLINE_HINT FHashBuilder& operator<<(const T& InData)
    {
        return Append(InData);
    }
 
    UE_FORCEINLINE_HINT uint32 GetHash() const
    {
        return ~Hash;
    }
 
private:
    uint32 Hash;
};