Getting confused with Structs

[Mateo_Mazzini]

Im starting to getting a bit confused with the way structs are managed in c++. In the bulls and cows part, we learnt that we can initialize structs like so:

struct BullsNCows{
int32 Bulls;
Int32 Cows;
};
// then

BullsNCows Points = {10, 5};

In this case we will have a Points struct of the type BullsNCows that has 10 bulls and 5 cows.
Now in this lecture I see that the teacher is calling another struct like this:

FCollisionQueryParams TraceParams(FName(TEXT("")), false, GetOwner());

I have the impression that it should’ve been

FCollisionQueryParams TraceParams{FName(TEXT("")), false, GetOwner()};

or

FCollisionQueryParams TraceParams = {FName(TEXT("")), false, GetOwner()};

are all of these options valid an in C++ the use of () or {} is almost interchangeable, or am I missing something here?

Another thing I don’t understand, I thought when you create an if statement with the name of a variable as a condition you were testing if the variable was a boolean returning true, but in this lecture the teacher writes:

if (ActorHit)

in this case ActorHit is an AActor, so what is the evaluation the if statement does?

Thanks!

[DanM]

@Mateo_Mazzini

are all of these options valid an in C++

They should be. Initialisation syntax in C++ is, by all accounts, insane
https://blog.tartanllama.xyz/initialization-is-bonkers/

@Mateo_Mazzini

in C++ the use of () or {} is almost interchangeable

Not quite. {} prefers constructors that take a std::initializer_list

#include <initializer_list>

class Example
{
public:
    Example(int); // 1
    Example(std::initializer_list<int>); // 2
};

int main()
{
    Example E1(1); // 1 gets called
    Example E2{ 1 }; // 2 gets called
}

I recommend only using {} when you need the one taking initializer_list, personally.
std::initializer_list is what’s being used here

TArray<int32> Bob{ 1, 2, 3, 4 };

Also personally, I never use = for initialising variables other than the primitive types.

@Mateo_Mazzini

in this case ActorHit is an AActor, so what is the evaluation the if statement does?

if (Pointer) is the same as if (Pointer != nullptr).
From the standard:

A prvalue of arithmetic, unscoped enumeration, pointer, or pointer-to-member type can be converted to a prvalue of type bool.

A zero value, null pointer value, or null member pointer value is converted to false; any other value is converted to true.

- (emph, mine) https://eel.is/c++draft/conv.bool

[Mateo_Mazzini]

Thank you so much for taking the time to go through all these question, really thorough!