EM_Task/CoreUObject/Public/UObject/StructOnScope.h

// Copyright Epic Games, Inc. All Rights Reserved.

#pragma once

#include "CoreMinimal.h"
#include "UObject/Class.h"
#include "UObject/WeakObjectPtr.h"
#include "UObject/Package.h"
#include "Templates/Casts.h"
#include "Templates/RemoveReference.h"

class FStructOnScope
{
protected:
    TWeakObjectPtr<const UStruct> ScriptStruct;
    uint8* SampleStructMemory;
    TWeakObjectPtr<UPackage> Package;
    /** Whether the struct memory is owned by this instance. */
    bool OwnsMemory;

    virtual void Initialize()
    {
        if (const UStruct* ScriptStructPtr = ScriptStruct.Get())
        {
            SampleStructMemory = (uint8*)FMemory::Malloc(ScriptStructPtr->GetStructureSize() ? ScriptStructPtr->GetStructureSize() : 1);
            ScriptStructPtr->InitializeStruct(SampleStructMemory);
            OwnsMemory = true;
        }
    }

public:
    FStructOnScope()
        : SampleStructMemory(nullptr), OwnsMemory(false)
    {
    }

    FStructOnScope(const UStruct* InScriptStruct)
        : ScriptStruct(InScriptStruct), SampleStructMemory(nullptr), OwnsMemory(false)
    {
        Initialize();
    }

    FStructOnScope(const UStruct* InScriptStruct, uint8* InData)
        : ScriptStruct(InScriptStruct), SampleStructMemory(InData), OwnsMemory(false)
    {
    }

    FStructOnScope(FStructOnScope&& InOther)
    {
        ScriptStruct       = InOther.ScriptStruct;
        SampleStructMemory = InOther.SampleStructMemory;
        OwnsMemory         = InOther.OwnsMemory;

        InOther.OwnsMemory = false;
        InOther.Reset();
    }

    FStructOnScope& operator=(FStructOnScope&& InOther)
    {
        if (this != &InOther)
        {
            Reset();

            ScriptStruct       = InOther.ScriptStruct;
            SampleStructMemory = InOther.SampleStructMemory;
            OwnsMemory         = InOther.OwnsMemory;

            InOther.OwnsMemory = false;
            InOther.Reset();
        }
        return *this;
    }

    FStructOnScope(const FStructOnScope&)            = delete;
    FStructOnScope& operator=(const FStructOnScope&) = delete;

    virtual bool OwnsStructMemory() const
    {
        return OwnsMemory;
    }

    virtual uint8* GetStructMemory()
    {
        return SampleStructMemory;
    }

    virtual const uint8* GetStructMemory() const
    {
        return SampleStructMemory;
    }

    virtual const UStruct* GetStruct() const
    {
        return ScriptStruct.Get();
    }

    virtual UPackage* GetPackage() const
    {
        return Package.Get();
    }

    virtual void SetPackage(UPackage* InPackage)
    {
        Package = InPackage;
    }

    virtual bool IsValid() const
    {
        return ScriptStruct.IsValid() && SampleStructMemory;
    }

    virtual void Destroy()
    {
        if (!OwnsMemory)
        {
            return;
        }

        if (const UStruct* ScriptStructPtr = ScriptStruct.Get())
        {
            if (SampleStructMemory)
            {
                ScriptStructPtr->DestroyStruct(SampleStructMemory);
            }
            ScriptStruct = nullptr;
        }

        if (SampleStructMemory)
        {
            FMemory::Free(SampleStructMemory);
            SampleStructMemory = nullptr;
        }
    }

    virtual void Reset()
    {
        Destroy();

        ScriptStruct       = nullptr;
        SampleStructMemory = nullptr;
        OwnsMemory         = false;
    }

    virtual ~FStructOnScope()
    {
        Destroy();
    }

    /** Re-initializes the scope with a specified UStruct */
    void Initialize(TWeakObjectPtr<const UStruct> InScriptStruct)
    {
        Destroy();
        ScriptStruct = InScriptStruct;
        Initialize();
    }
};

/**
 * Typed FStructOnScope that exposes type-safe access to the wrapped struct
 * @note The second template argument is there to restrict to type that are actually USTRUCT.
 *		It will be replaced to a static_assert with a better compiler error with a "is ustruct" type trait
 */
template <typename T, typename = decltype(TBaseStructure<T>::Get())>
class TStructOnScope final: public FStructOnScope
{
public:
    TStructOnScope()                                    = default;
    virtual ~TStructOnScope()                           = default;

    TStructOnScope(TStructOnScope&& InOther)            = default;
    TStructOnScope& operator=(TStructOnScope&& InOther) = default;

    template <typename U, typename = typename TEnableIf<TIsDerivedFrom<typename TRemoveReference<U>::Type, T>::IsDerived, void>::Type>
    explicit TStructOnScope(U&& InStruct)
        : FStructOnScope(TBaseStructure<typename TRemoveReference<U>::Type>::Get())
    {
        if (const UScriptStruct* ScriptStructPtr = ::Cast<UScriptStruct>(ScriptStruct.Get()))
        {
            ScriptStructPtr->CopyScriptStruct(SampleStructMemory, &InStruct);
        }
    }

    template <typename U, typename = typename TEnableIf<TIsDerivedFrom<typename TRemoveReference<U>::Type, T>::IsDerived, void>::Type>
    TStructOnScope& operator=(U&& InStruct)
    {
        Initialize(TBaseStructure<typename TRemoveReference<U>::Type>::Get());
        if (const UScriptStruct* ScriptStructPtr = ::Cast<UScriptStruct>(ScriptStruct.Get()))
        {
            ScriptStructPtr->CopyScriptStruct(SampleStructMemory, &InStruct);
        }
        return *this;
    }

    /**
     * Initialize the TStructOnScope as a struct of type U which needs to derive from T
     * @params InArgs The arguments to pass to the constructor of type U
     */
    template <typename U, typename = typename TEnableIf<TIsDerivedFrom<typename TRemoveReference<U>::Type, T>::IsDerived, void>::Type, typename... TArgs>
    void InitializeAs(TArgs&&... InArgs)
    {
        Destroy();
        if (UScriptStruct* ScriptStructPtr = TBaseStructure<U>::Get())
        {
            ScriptStruct       = ScriptStructPtr;
            SampleStructMemory = (uint8*)FMemory::Malloc(ScriptStructPtr->GetStructureSize() ? ScriptStructPtr->GetStructureSize() : 1);
            new (SampleStructMemory) U(Forward<TArgs>(InArgs)...);
            OwnsMemory = true;
        }
    }

    /**
     * Initialize the TStructOnScope from a FStructOnScope containing data that derives from T
     * @params InOther The FStructOnScope to initialize from
     * @return True if the conversion was successful, false otherwise
     */
    bool InitializeFrom(const FStructOnScope& InOther)
    {
        if (const UScriptStruct* ScriptStructPtr = ::Cast<const UScriptStruct>(InOther.GetStruct()))
        {
            if (ScriptStructPtr->IsChildOf(TBaseStructure<T>::Get()))
            {
                Initialize(ScriptStructPtr);
                ScriptStructPtr->CopyScriptStruct(SampleStructMemory, InOther.GetStructMemory());
                return true;
            }
        }
        else
        {
            Destroy();
            return true;
        }
        return false;
    }

    /**
     * Initialize the TStructOnScope from a FStructOnScope containing data that derives from T
     * @params InOther The FStructOnScope to initialize from
     * @return True if the conversion was successful, false otherwise
     */
    bool InitializeFrom(FStructOnScope&& InOther)
    {
        if (this == &InOther)
        {
            return true;
        }
        if (const UScriptStruct* ScriptStructPtr = ::Cast<const UScriptStruct>(InOther.GetStruct()))
        {
            if (ScriptStructPtr->IsChildOf(TBaseStructure<T>::Get()) && InOther.OwnsStructMemory())
            {
                *static_cast<FStructOnScope*>(this) = MoveTemp(InOther);
                return true;
            }
        }
        else
        {
            Destroy();
            return true;
        }
        return false;
    }

    /**
     * Initialize the TStructOnScope from a FStructOnScope containing data that derives from T
     * @params InOther The FStructOnScope to initialize from (will assert if it contains an invalid type to store for T)
     */
    void InitializeFromChecked(const FStructOnScope& InOther)
    {
        if (!InitializeFrom(InOther))
        {
            UE_LOG(LogClass, Fatal, TEXT("Initialize of %s to %s failed"), *InOther.GetStruct()->GetName(), *TBaseStructure<T>::Get()->GetName());
        }
    }

    /**
     * Initialize the TStructOnScope from a FStructOnScope containing data that derives from T
     * @params InOther The FStructOnScope to initialize from (will assert if it contains an invalid type to store for T)
     */
    void InitializeFromChecked(FStructOnScope&& InOther)
    {
        if (!InitializeFrom(MoveTemp(InOther)))
        {
            UE_LOG(LogClass, Fatal, TEXT("Initialize of %s failed"), *TBaseStructure<T>::Get()->GetName());
        }
    }

    T* Get() const
    {
        return reinterpret_cast<T*>(SampleStructMemory);
    }

    T* operator->() const
    {
        return Get();
    }

    explicit operator bool() const
    {
        return IsValid();
    }

    template <typename U>
    U* Cast()
    {
        if (GetStruct()->IsChildOf(TBaseStructure<U>::Get()))
        {
            return reinterpret_cast<U*>(SampleStructMemory);
        }
        return nullptr;
    }

    template <typename U>
    const U* Cast() const
    {
        return const_cast<TStructOnScope*>(this)->Cast<U>();
    }

    template <typename U>
    U* CastChecked()
    {
        U* Result = nullptr;
        if (!IsValid())
        {
            UE_LOG(LogClass, Fatal, TEXT("Cast of nullptr to %s failed"), *TBaseStructure<U>::Get()->GetName());
            return Result;
        }

        Result = Cast<U>();
        if (!Result)
        {
            UE_LOG(LogClass, Fatal, TEXT("Cast of %s to %s failed"), *TBaseStructure<T>::Get()->GetName(), *TBaseStructure<U>::Get()->GetName());
        }
        return Result;
    }

    template <typename U>
    const U* CastChecked() const
    {
        return const_cast<TStructOnScope*>(this)->CastChecked<U>();
    }

    friend FArchive& operator<<(FArchive& Ar, TStructOnScope& InStruct)
    {
        if (Ar.IsLoading())
        {
            FString StructPath;
            Ar << StructPath;
            if (!StructPath.IsEmpty())
            {
                UScriptStruct* ScriptStructPtr = FindObject<UScriptStruct>(nullptr, *StructPath, false);
                if (ScriptStructPtr == nullptr || !ScriptStructPtr->IsChildOf(TBaseStructure<T>::Get()))
                {
                    Ar.SetError();
                    return Ar;
                }
                InStruct.ScriptStruct = ScriptStructPtr;
                InStruct.Initialize();
                ScriptStructPtr->SerializeItem(Ar, InStruct.SampleStructMemory, nullptr);
            }
        }
        // Saving
        else
        {
            FString StructPath;
            if (UScriptStruct* ScriptStructPtr = const_cast<UScriptStruct*>(::Cast<UScriptStruct>(InStruct.ScriptStruct.Get())))
            {
                StructPath = ScriptStructPtr->GetPathName();
                Ar << StructPath;
                ScriptStructPtr->SerializeItem(Ar, InStruct.SampleStructMemory, nullptr);
            }
            else
            {
                Ar << StructPath;
            }
        }

        return Ar;
    }

private:
    using FStructOnScope::Destroy;
    using FStructOnScope::GetPackage;
    using FStructOnScope::GetStructMemory;
    using FStructOnScope::Initialize;
    using FStructOnScope::OwnsStructMemory;
    using FStructOnScope::SetPackage;
};

/**
 * Allocates a new struct of type U with the given arguments and returns it as a Typed StructOnScope of type T.
 *
 * @param Args The arguments to pass to the constructor of U.
 *
 * @return A TStructOnScope<T> which holds a struct to a newly-constructed U with the specified Args.
 */
template <typename T, typename U = T, typename... TArgs>
FORCEINLINE TStructOnScope<T> MakeStructOnScope(TArgs&&... Args)
{
    TStructOnScope<T> Struct;
    Struct.template InitializeAs<U>(Forward<TArgs>(Args)...);
    return Struct;
}