UE4 C++ Create Background task with using Async() function

Question

I want to create a background task with using Async function: (Async | Unreal Engine Documentation) I read and follow the documentation but i’ve got an compile error. This is the code:

int32 TestFunc()
{
    GEngine->AddOnScreenDebugMessage(0,5,FColor::Red,TEXT("This is an async task"));
    return 123;
}

TUniqueFunction<int32()> Task = TestFunc;


// Called when the game starts or when spawned
void ATempActor::BeginPlay()
{
    Super::BeginPlay();
    auto Result = Async(EAsyncExecution::Thread,Task);
}

There is no intellisense error. And the compile error is :

Async.h(297): [C2280] ‘TUniqueFunction<int32 (void)>::TUniqueFunction(const TUniqueFunction<int32 (void)> &)’: attempting to reference a deleted function

How can i use Async() function corectly? Thx a lot in advance.