Unreal engine and C++/Blueprints - Interfaces
I've been spending some more time familiarizing myself with parts of unreal and while I was working on an interface in C++ I came across some stuff in the docs that sent me down a rabit hole
Here's the docs to avoid my explanation of how I discovered it works
Reference to creating and implementing interfaces.
This wiki article was originally written by Rama and received contributions from HuntaKiller, DarkGaze, and Ruhrpottpatiot.
For interfaces specifically it is possible to make an interface that can be overwritten in either C++ or blueprints. In order to make that work they have changed the way you would create said interface.
So normally if you were creating a C++ only interface, you'd probably define a function something along the lines of:
virtual bool MyInterfaceFunction() = 0;
and then where ever you then inherit from said interface, you'd then do
bool MyInterfaceFunction() override;
and then you'd do your implementation in a .cpp file
However this is NOT how unreal want you to do overrides if you want to be able to have the option to override in C++ OR Blueprints.
Instead in your interface itself you have the following:
your interface class would have the following decorator:
UINTERFACE(BlueprintType)
you would then define the function you want to override like so:
UFUNCTION(BlueprintCallable, BlueprintNativeEvent, Category="Blueprint/C++ Implementable")
bool MyInterfaceFunction();
then wherever you inherit this interface you would then put
Category="Blueprint/C++ Implementable")
bool MyInterfaceFunction();
and then to override in C++ you'd do this:
bool MyInterfaceFunction_Implementation() override;
which is a signature that Unreal will generate for your interface class when you compile it.
and then according to the docs if you then ever access an instance of this interface to call this method, you will need to call this function instead
myInterfaceInstance->Execute_MyInterfaceFunction();
Which again is generated by unreal for your blueprint class and will be "Execute_" followed by the name of your function with a matching signature.
I just thought this was really interesting as I assume this is how they allow the C++ call to not care whether this interface function calls a C++ implementation or a blueprint one.
And it was a little confusing before I got my head round why they would want to do it this way.
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