EM_Task/CoreUObject/Public/UObject/ConstructorHelpers.h

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

/*=============================================================================
        ConstructorHelpers.h: Constructor helper templates
=============================================================================*/

#pragma once

#include "CoreMinimal.h"
#include "Templates/SubclassOf.h"
#include "UObject/Package.h"
#include "UObject/GCObject.h"

namespace ConstructorHelpersInternal
{
template <typename T>
inline T* FindOrLoadObject(FString& PathName, uint32 LoadFlags)
{
    // If there is no dot, add a dot and repeat the object name.
    int32 PackageDelimPos = INDEX_NONE;
    PathName.FindChar(TCHAR('.'), PackageDelimPos);
    if (PackageDelimPos == INDEX_NONE)
    {
        int32 ObjectNameStart = INDEX_NONE;
        PathName.FindLastChar(TCHAR('/'), ObjectNameStart);
        if (ObjectNameStart != INDEX_NONE)
        {
            const FString ObjectName = PathName.Mid(ObjectNameStart + 1);
            PathName += TCHAR('.');
            PathName += ObjectName;
        }
    }

    UClass* Class = T::StaticClass();
    Class->GetDefaultObject();  // force the CDO to be created if it hasn't already
    T* ObjectPtr = LoadObject<T>(NULL, *PathName, nullptr, LoadFlags);
    if (ObjectPtr)
    {
        ObjectPtr->AddToRoot();
    }
    return ObjectPtr;
}

template <>
inline UPackage* FindOrLoadObject<UPackage>(FString& PathName, uint32 LoadFlags)
{
    // If there is a dot, remove it.
    int32 PackageDelimPos = INDEX_NONE;
    PathName.FindChar(TCHAR('.'), PackageDelimPos);
    if (PackageDelimPos != INDEX_NONE)
    {
        PathName.RemoveAt(PackageDelimPos, 1, false);
    }

    // Find the package in memory.
    UPackage* PackagePtr = FindPackage(nullptr, *PathName);
    if (!PackagePtr)
    {
        // If it is not in memory, try to load it.
        PackagePtr = LoadPackage(nullptr, *PathName, LoadFlags);
    }
    if (PackagePtr)
    {
        PackagePtr->AddToRoot();
    }
    return PackagePtr;
}

inline UClass* FindOrLoadClass(FString& PathName, UClass* BaseClass)
{
    // If there is no dot, add ".<object_name>_C"
    int32 PackageDelimPos = INDEX_NONE;
    PathName.FindChar(TCHAR('.'), PackageDelimPos);
    if (PackageDelimPos == INDEX_NONE)
    {
        int32 ObjectNameStart = INDEX_NONE;
        PathName.FindLastChar(TCHAR('/'), ObjectNameStart);
        if (ObjectNameStart != INDEX_NONE)
        {
            const FString ObjectName = PathName.Mid(ObjectNameStart + 1);
            PathName += TCHAR('.');
            PathName += ObjectName;
            PathName += TCHAR('_');
            PathName += TCHAR('C');
        }
    }
    UClass* LoadedClass = StaticLoadClass(BaseClass, NULL, *PathName);
    if (LoadedClass)
    {
        LoadedClass->AddToRoot();
    }
    return LoadedClass;
}
}  // namespace ConstructorHelpersInternal

struct COREUOBJECT_API ConstructorHelpers
{
public:
    template <class T>
    struct FObjectFinder: public FGCObject
    {
        T* Object;
        FObjectFinder(const TCHAR* ObjectToFind, uint32 InLoadFlags = LOAD_None)
        {
            CheckIfIsInConstructor(ObjectToFind);
            FString PathName(ObjectToFind);
            StripObjectClass(PathName, true);

            Object = ConstructorHelpersInternal::FindOrLoadObject<T>(PathName, InLoadFlags);
            ValidateObject(Object, PathName, ObjectToFind);
        }
        bool Succeeded() const
        {
            return !!Object;
        }

        virtual void AddReferencedObjects(FReferenceCollector& Collector) override
        {
            Collector.AddReferencedObject(Object);
        }

        virtual FString GetReferencerName() const override
        {
            return TEXT("FObjectFinder");
        }
    };

    template <class T>
    struct FObjectFinderOptional: public FGCObject
    {
    private:
        T* Object;
        const TCHAR* ObjectToFind;
        uint32 LoadFlags;

    public:
        FObjectFinderOptional(const TCHAR* InObjectToFind, uint32 InLoadFlags = LOAD_None)
            : Object(nullptr), ObjectToFind(InObjectToFind), LoadFlags(InLoadFlags)
        {
        }
        T* Get()
        {
            if (!Object && ObjectToFind)
            {
                CheckIfIsInConstructor(ObjectToFind);
                FString PathName(ObjectToFind);
                StripObjectClass(PathName, true);

                Object           = ConstructorHelpersInternal::FindOrLoadObject<T>(PathName, LoadFlags);

                bool WarnMissing = (LoadFlags & (LOAD_Quiet | LOAD_NoWarn)) == 0;

                if (Object || WarnMissing)
                {
                    ValidateObject(Object, PathName, ObjectToFind);
                }

                ObjectToFind = nullptr;  // don't try to look again
            }
            return Object;
        }
        bool Succeeded()
        {
            return !!Get();
        }

        virtual void AddReferencedObjects(FReferenceCollector& Collector) override
        {
            Collector.AddReferencedObject(Object);
        }

        virtual FString GetReferencerName() const override
        {
            return TEXT("FObjectFinderOptional");
        }
    };

    template <class T>
    struct FClassFinder: public FGCObject
    {
        TSubclassOf<T> Class;
        FClassFinder(const TCHAR* ClassToFind)
        {
            CheckIfIsInConstructor(ClassToFind);
            FString PathName(ClassToFind);
            StripObjectClass(PathName, true);
            Class = ConstructorHelpersInternal::FindOrLoadClass(PathName, T::StaticClass());
            ValidateObject(*Class, PathName, *PathName);
        }
        bool Succeeded()
        {
            return !!*Class;
        }

        virtual void AddReferencedObjects(FReferenceCollector& Collector) override
        {
            UClass* ReferencedClass = Class.Get();
            Collector.AddReferencedObject(ReferencedClass);
            Class = ReferencedClass;
        }

        virtual FString GetReferencerName() const override
        {
            return TEXT("FClassFinder");
        }
    };

public:
    /** If there is an object class, strips it off. */
    static void StripObjectClass(FString& PathName, bool bAssertOnBadPath = false);

private:
    static void ValidateObject(UObject* Object, const FString& PathName, const TCHAR* ObjectToFind)
    {
        if (!Object)
        {
            FailedToFind(ObjectToFind);
        }
#if UE_BUILD_DEBUG
        else
        {
            CheckFoundViaRedirect(Object, PathName, ObjectToFind);
        }
#endif
    }

    static void FailedToFind(const TCHAR* ObjectToFind);
    static void CheckFoundViaRedirect(UObject* Object, const FString& PathName, const TCHAR* ObjectToFind);
    static void CheckIfIsInConstructor(const TCHAR* ObjectToFind);
};