I know it is possible to cast thing in Unreal using Cast Keyword
Cast<Object>(object...)
But I was wondering if we could use:
I created a Interface (pure virtual class), but I saw some problems when doing reinterpret_cast with it.
E.g.
I can have:
class IMyInterface {
void doSomething() = 0;
};
UCLASS()
class MYTEST_API My_Character : public ACharacter, public IMyInterface
{
GENERATED_BODY()
But when I do reinterpret_cast<IMyInterface*> my object is not fully loaded and sometimes the program crashes.
Is there any restrictions doing these common c++ cast in Unreal Engine?
But I was wondering if we could use:
- static_cast
- dynamic_cast
- reinterpret_cast
Yes, of course you can use these. However, there are some restrictions and do's and don'ts here.
First off, the only casts you'll probably need are the Cast<T>() and StaticCast<T> which Unreal provides. Cast<T>() uses reflection to determine the passed in type and the templated type and try to match them, returning a nullptr on failure. Note that, because of the nature of Unreals reflection, Cast<T>() only works on types that are USTRUCTs or UCLASSes. You can look into its inner workings here in the source.
StaticCast<T>() is internally just the static_cast<T>() that you are used to. But there are reasons why it exists:
This exists to avoid a Visual Studio bug where using a cast to forward an rvalue reference array argument to a pointer parameter will cause bad code generation. Wrapping the cast in a function causes the correct code to be generated.
Using a reinterpret_cast on an UObject is most definitely the wrong approach. Did you know that you can just define UINTERFACE implementations and cast typesafe using Cast<T>()?
A major issue with that is that holding a reference to an interface does not guarantee the lifetime of the object. So, if you want to keep it alive, you probably want to store the UObject* of the interface as a reference, either in a TStrongObjectPtr or as a UPROPERTY() in another UCLASS().