StructUtils.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "Templates/UnrealTypeTraits.h"
#include "UObject/Class.h"
 
namespace UE::StructUtils
{
    template <typename T>
    void CheckStructType()
    {
        static_assert(!TIsDerivedFrom<T, struct FInstancedStruct>::IsDerived &&
                      !TIsDerivedFrom<T, struct FStructView>::IsDerived &&
                      !TIsDerivedFrom<T, struct FConstStructView>::IsDerived &&
                      !TIsDerivedFrom<T, struct FSharedStruct>::IsDerived &&
                      !TIsDerivedFrom<T, struct FConstSharedStruct>::IsDerived, "It does not make sense to create wrapper over these types.");
    }
 
    template <typename T>
    void CheckWrapperType()
    {
        static_assert(TIsDerivedFrom<T, struct FInstancedStruct>::IsDerived
            || TIsDerivedFrom<T, struct FStructView>::IsDerived
            || TIsDerivedFrom<T, struct FConstStructView>::IsDerived
            || TIsDerivedFrom<T, struct FSharedStruct>::IsDerived
            || TIsDerivedFrom<T, struct FConstSharedStruct>::IsDerived, "This function is meant to compare contents of wrapped structs.");
    }
 
    template<typename T>
    T& GetStructRef(const UScriptStruct* ScriptStruct, void* StructMemory)
    {
        check(StructMemory != nullptr);
        check(ScriptStruct != nullptr);
        checkf(ScriptStruct == TBaseStructure<T>::Get() || ScriptStruct->IsChildOf(TBaseStructure<T>::Get()),
            TEXT("Incompatible struct types: Cannot cast '%s' to '%s'"),
            *ScriptStruct->GetPathName(),
            *TBaseStructure<T>::Get()->GetPathName());
        return *((T*)StructMemory);
    }
 
    template<typename T>
    T* GetStructPtr(const UScriptStruct* ScriptStruct, void* StructMemory)
    {
        if (StructMemory != nullptr 
            && ScriptStruct 
            && (ScriptStruct == TBaseStructure<T>::Get()
                || ScriptStruct->IsChildOf(TBaseStructure<T>::Get())))
        {
            return ((T*)StructMemory);
        }
        return nullptr;
    }
 
    template<typename T, typename BaseStructT>
    T* GetStructPtr(const UScriptStruct* ScriptStruct, void* StructMemory)
    {
        if constexpr (std::is_same_v<BaseStructT, std::decay_t<T>>)
        {
#if WITH_EDITOR || !UE_BUILD_SHIPPING
            if (StructMemory && ScriptStruct)
            {
                // An extra guard to verify that ScriptStruct is actually safe to cast to T
                if (ensureAlwaysMsgf(ScriptStruct == TBaseStructure<T>::Get() || ScriptStruct->IsChildOf(TBaseStructure<T>::Get()),
                    TEXT("Incompatible struct types: Cannot cast '%s' to '%s'. Falling back to return nullptr, but this may crash in shipping!"), *ScriptStruct->GetPathName(), *TBaseStructure<T>::Get()->GetPathName()))
                {
                    return ((T*)StructMemory);
                }
            }
            return nullptr;
#else
            return ((T*)StructMemory);
#endif
        }
        else
        {
            return GetStructPtr<T>(ScriptStruct, StructMemory);
        }
    }
 
    template<typename T>
    const T& GetStructRef(const UScriptStruct* ScriptStruct, const void* StructMemory)
    {
        return GetStructRef<T>(ScriptStruct, const_cast<void*>(StructMemory));
    }
 
    template<typename T>
    const T* GetStructPtr(const UScriptStruct* ScriptStruct, const void* StructMemory)
    {
        return GetStructPtr<T>(ScriptStruct, const_cast<void*>(StructMemory));
    }
 
    template<typename T, typename BaseStructT>
    const T* GetStructPtr(const UScriptStruct* ScriptStruct, const void* StructMemory)
    {
        return GetStructPtr<T, BaseStructT>(ScriptStruct, const_cast<void*>(StructMemory));
    }
 
    inline void CalcMidIndexAndCount(int32 ArrayNum, int32& InOutIndex, int32& InOutCount)
    {
        // Clamp minimum index at the start of the range, adjusting the length down if necessary
        const int32 NegativeIndexOffset = (InOutIndex < 0) ? InOutIndex : 0;
        InOutCount += NegativeIndexOffset;
        InOutIndex -= NegativeIndexOffset;
 
        // Clamp maximum index at the end of the range
        InOutIndex = (InOutIndex > ArrayNum) ? ArrayNum : InOutIndex;
 
        // Clamp count between 0 and the distance to the end of the range
        InOutCount = FMath::Clamp(InOutCount, 0, (ArrayNum - InOutIndex));
    }
}