RunOnce Delegate in Unreal Engine

RunOnce.cpp

#include "CoreMinimal.h"

class FRunOnce
{
public:
	FORCEINLINE FRunOnce() : bHasRan(false) {}
	FORCEINLINE explicit FRunOnce(const bool bStartClosed) : bHasRan(bStartClosed) {}
	FORCEINLINE bool Execute() { return bHasRan ? false : bHasRan = true; }
	FORCEINLINE void Reset() { bHasRan = false; }
private:
	bool bHasRan;
};


template <typename... T>
class TRunOnce : TDelegate<void(T...)>
{
public:
	FORCEINLINE TRunOnce() : RunOnce(MakeShared<FRunOnce>(false)) {}
	FORCEINLINE explicit TRunOnce(const bool bStartClosed) : RunOnce(MakeShared<FRunOnce>(bStartClosed)) {}

	FORCEINLINE bool ExecuteOnce(T... Args)
	{
		return RunOnce->Execute() ? TDelegate<void(T...)>::ExecuteIfBound(Args...) : false;
	}

	FORCEINLINE void Reset()
	{
		RunOnce->Reset();
	}
	
	template<typename FunctorType, typename... VarTypes>
	FORCEINLINE void BindLambda(FunctorType&& Functor, VarTypes&&... Vars)
	{
		TDelegate<void(T...)>::BindLambda(MoveTemp(Functor), MoveTemp(Vars)...);
	}
	
private:
	TSharedPtr<FRunOnce> RunOnce;
};


class FSandboxUtilitiesModule : public IModuleInterface
{
public:
	/** IModuleInterface implementation */
	virtual void StartupModule() override;
	virtual void ShutdownModule() override;

private:
	TSharedPtr<TRunOnce<FString>> RunOnceDelegate;
};

void FSandboxUtilitiesModule::StartupModule()
{
	RunOnceDelegate = MakeShared<TRunOnce<FString>>();
	
	RunOnceDelegate->BindLambda([] (const FString& Message)
	{
		UE_LOG(LogTemp, Warning, TEXT("Hello from SandboxUtilitiesModule: %s"), *Message);
	});

  // Should only run twice total, one for each loop before and after reset.
  
	for (int i = 0; i < 10; ++i)
	{
		RunOnceDelegate->ExecuteOnce(FString(TEXT("Testing RunOnceDelegate")));
	}
  
	RunOnceDelegate->Reset();
  
	for (int i = 0; i < 10; ++i)
	{
		RunOnceDelegate->ExecuteOnce(FString(TEXT("Testing RunOnceDelegate")));
	}
}

void FSandboxUtilitiesModule::ShutdownModule()
{
	// This function may be called during shutdown to clean up your module.  For modules that support dynamic reloading,
	// we call this function before unloading the module.
}