UE4 C++ Custom MACRO

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A macro is just a dumb text replacement that happens before compilation happens. It would only cause a crash if the expanded code would crash.

They’re best avoid precisely because they’re just a dumb text replacement. You can’t debug them, the compiler can’t tell you if you messed up as it will only see what the macro expanded to, etc.

I suggest you read the answer for this SO post

c++ - Why are preprocessor macros evil and what are the alternatives? - Stack Overflow

Well if you have a base class that has SetupWidget then you can just use that base class and make it a normal function

UUMGBase* Foo::Setup(TSubclassOf<UUMGBase> StoreUIClass)
{
    UUMGBase* StoreUI = CreateWidget<UUMGBase>(GetWorld(), StoreUIClass);
    if (StoreUI)
        StoreUI->SetupWidget();
    return StoreUI;
}

void Foo::Bar()
{
    UUMGBase* Thing = Setup(UIClass);
    if (Thing)
    {
        //use Thing
    }
}

Edit: Oh and you can do what the engine does and provide a template version that calls the other i.e. if you need a derived type you would do

UDerivedUMG* Thing = Cast<UDerivedUMG>(Setup(UIClass));
if (Thing)
{
    // use Thing
}

which is too much typing for our delicate hands. If you create a template that does

template<class T>
T* Setup(Blah)
{
    return Cast<T>(Setup(Blah));
}

You can then just write

UDerivedUMG* Thing = Setup<UDerivedUMG>(UIClass);
if (Thing)
{
    // use Thing
}

So this would just be syntactic sugar for C++ code. The first should still work for BP. This is actually what the templated versions of GetController, GetPawn, GetOwner et al. do

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