Make Smart Pointers work with Forward Declarations

General Feedback & Requests
1

Currently, TWeakObjectPtr does not support forward declarations, which can be a bit of a nightmare when creating custom structs that you want to reuse. For example:

// This is a header file included by all classes in the game, container a series of enums, structs etc. Similar to Shootergame.
GESTypes.h



USTRUCT(BlueprintType)
struct FMissionTarget
{
	GENERATED_USTRUCT_BODY()

	// Component we're targeting
	UPROPERTY(BlueprintReadOnly, Category = "Target")
	TWeakObjectPtr<USceneComponent> TargetComponent;

	// Socket on the component we're targeting
	UPROPERTY(BlueprintReadOnly, Category = "Target")
	FName TargetSocket;

	// ID of the mission this target belongs to
	UPROPERTY(BlueprintReadOnly, Category = "Target")
	int32 TargetMissionID;

	// Cached Pointer to the Mission
	UPROPERTY()
	TWeakObjectPtr<const UActiveMission> TargetMissionPtr;

	FMissionTarget()
		: TargetComponent(NULL)
		, TargetSocket(NAME_None)
		, TargetMissionID(-1)
		, TargetMissionPtr(nullptr)
	{}
};

The above code does not allow compilation to occur, because it doesn’t know what ‘UActiveMission’ is (which is a custom UObject class). Using a forward declaration


TWeakObjectPtr<const class UActiveMission> TargetMissionPtr;

still prevents compilation, because it can’t determine the template type as a UObject.

UActiveMission already includes this file and needs to do so, which makes compilation impossible and creates circular dependencies.

2

Are you sure there isn’t something funkier going on? I’ve been able to forward declare weak object pointer types just fine, and searching for “TweakObjectPtr<class” shows plenty of examples in the engine.

3

You might need to move your constructor to the cpp since it’s probably expecting the definition there rather than the forward declaration in the TWeakObjectPtr part.

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