How to pass Enum Bitflags as parameter of UFUNCTION with default value

Development Programming & Scripting
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1

Hello everyone,

I’m stuck on a pretty weird thing and in fact I think I’m missing something.

I Made an enum class as a bitflags enum like this :

/**
 * test Bitflags
 */
UENUM(BlueprintType, meta=(Bitflags, UseEnumValuesAsMaskValuesInEditor=true))
enum class EThingFilter : uint8
{
	None				= 0b000000 UMETA(DisplayName="None"),
	IgnoreNullId		= 0b000001 UMETA(DisplayName="IgnoreNullId"),
	OnlyNullId			= 0b000010 UMETA(DisplayName="OnlyNullId"),
	EvenId				= 0b000100 UMETA(DisplayName="EvenId"),
	OddId				= 0b001000 UMETA(DisplayName="OddId"),
	OnlyAlphaName		= 0b010000 UMETA(DisplayName="OnlyAlphaName"),
	OnlyNumericName		= 0b100000 UMETA(DisplayName="OnlyNumericName")
};
ENUM_CLASS_FLAGS(EThingFilter);

And then in a test UObject, I’m trying to implement a UFUNCTION like this :

UCLASS(BlueprintType, Blueprintable)
class TESTDIVERS_API UThingArrayStorage : public UObject
{
	GENERATED_BODY()
public:
	
	UPROPERTY()
	TArray<UThing*> Things;

	UPROPERTY(BlueprintGetter=GetInstanceName, BlueprintSetter=SetInstanceName)
	FString Name;


	UFUNCTION(BlueprintCallable, Category="Test")
	TArray<UThing*> FilterThings(UPARAM(meta = (Bitmask, BitmaskEnum = "EThingFilter")) int32 Filter );
};

I want to be able to pass something like EThingFilter::OddId & EThingFilter::OnlyAlphaName to this parameter. And when I do this, the code won’t compile.
Is it possible ? Or Am I in the wrong direction ?

Thanks.

PS: Note that if I pass an integer it compiles.

2

You’ve not shown the actual code that doesn’t compile and the actual error that is thrown as a starting point but I will go ahead and assume that you are not using the correct operator when passing the flags. :wink:

The proper operator in this case is bitwise or (|) not bitwise and (&);

Try FilterThings( EThingFilter::OddId | EThingFilter::OnlyAlphaName ); and tell how it went.

3

Thanks for your answer,

In fact I’ve posted the entire code, and I get an error when I try to put default values to the ufunction definition

tUCLASS(BlueprintType, Blueprintable)
class TESTDIVERS_API UThingArrayStorage : public UObject
{
	GENERATED_BODY()
public:
	
	UPROPERTY()
	TArray<UThing*> Things;

	UPROPERTY(BlueprintGetter=GetInstanceName, BlueprintSetter=SetInstanceName)
	FString Name;


	UFUNCTION(BlueprintCallable, Category="Test")
	TArray<UThing*> FilterThings(UPARAM(meta = (Bitmask, BitmaskEnum = "EThingFilter")) int32 Filter =   EThingFilter::OddId | EThingFilter::OnlyAlphaName );
};

And in fact I wanted to use, but maybe I’m wrong, FilterThing with Id that are Odd and Name with only alphaNum. That’s why I used & bitwise (&). It’s only a silly test to try to understant Bitflags.
But The real problem is that When I try the code above The compiler complains.
But again thank you for your answer.

4

Hm… Is it possible it doesn’t want to make the implicit int conversion?
Also can you remove the UPARAM stuff in cast that’s doing something strange.

TArray<UThing*> FilterThings(uint8 Filter = EThingFilter::OddId | EThingFilter::OnlyAlphaName );

Does this produce the same error or not? Also what’s the text of the error exactly?

5

I think you pointed out.
To answer your question the error I get was :

Cannot initialize parameter 'Filter' of type int32 with EThingFilter

And When I try Your code I’ve got :

Cannot initialize parameter 'Filter' of type uint8 with EThingFilter

So You’ve pointed out the thing.

it doesn’t want to make the implicit int conversion

And now if I do :

uint8 Filter = StaticCast<uint8>(EThingFilter::OddId | EThingFilter::OnlyAlphaName)

UHT complains that :

C++ Default parameter not parsed: Filter 'StaticCast<uint8>(EThingFilter::OddId | EThingFilter::OnlyAlphaName)' [UnrealHeaderTool Error

So I tried to StaticCast to uint8 with :

UFUNCTION(BlueprintCallable, Category="DTFluxTest")
	TArray<UDTFluxThing*> FilterThings(UPARAM(meta = (Bitmask, BitmaskEnum = "EThingFilter")) int32 Filter = StaticCast<uint8>(EThingFilter::OddId | EThingFilter::OnlyAlphaName));

Resulting in the same error.
And then I removed the exposition to blueprint like so :

UFUNCTION()
	TArray<UDTFluxThing*> FilterThings(UPARAM(meta = (Bitmask, BitmaskEnum = "EThingFilter")) int32 Filter = StaticCast<uint8>(EThingFilter::OddId | EThingFilter::OnlyAlphaName));

And then it compiles. But can’t test it has it’s not exposed in BP… But Maybe it can help understand.