C++-style Singletons in Unreal Engine

Coming from other C++-based game dev, you might be used to having singletons that are globally-accessible. With Unreal it requires a bit more work.

How to set up a vanilla C++ singleton

Don't.

Seriously in Unreal you will cause more problems than you solve.

• Easy to leave instances hanging around between using Run Game in the Editor
• Easy to create instances from the Class Default Object being loaded, or viewing a Blueprint subclass in-editor
• Nightmare for automated testing.

No but seriously, how do I do it?

Have you considered some of the many alternatives?

Add your code to some of the easily-accessible classes like AGameState, APlayerState, and use UGameplayStatics helper functions to get access to them.

You could use subsystems, a more Unreal but decoupled way of making something globally-accessible.

What about making a plugin of your code, and accessing the code through that?

Hey kid, over here….

OK so you really want to know? Here's the gross hacky way to do it.

UBUIMyEvilSingleton* UBUIMyEvilSingleton::Instance = nullptr;

UBUIMyEvilSingleton::UBUIMyEvilSingleton( const FObjectInitializer& ObjectInitializer )
	: Super( ObjectInitializer )
{
	// Don't set up Singleton instance in CDO constructor
	// or other Unreal-style constructors
	if ( !HasAnyFlags( RF_ClassDefaultObject
		| RF_NeedLoad
		| RF_NeedPostLoad
		| RF_NeedPostLoadSubobjects ) )
	{
		ensureMsgf( pInstance == nullptr, TEXT( "Uh-oh two singletons!" ) );
		pInstance = this;
	}
}

UBUIMyEvilSingleton::BeginDestroy()
{
	if ( pSingleton != nullptr )
	{
		if ( ensureMsgf( pSingleton == this, TEXT( "We have a singleton that isn't this!" ) )
		{
			pInstance = nullptr;
		}
	}
}