Accepted answer (in UE4 answerhub) to: "How can I create Blueprints with multiple exec output pins in C++?" Does not work for multi exec + data?

Development Programming & Scripting C++
1

I am trying to add a “better for loop” in my blueprint function library.
I came across the question in the title, and implemented the following psuedo-code from the answer from that question:

 // .h
 
 UENUM(BlueprintType)
 enum class EMyEnum : uint8
 {
     BranchA,
     BranchB
 };
 
 UFUNCTION(BlueprintCallable, Category = "Stuff", Meta = (ExpandEnumAsExecs = "Branches"))
 void DoSomeBranch(int32 SomeInput, EMyEnum& Branches)
 
 
 // .cpp
 
 void AMyClass::DoSomeBranch(int32 SomeInput, EMyEnum& Branches)
 {
     if (SomeInput == 1)
     {
         Branches = EMyEnum::BranchA;
     }
     else
     {
         Branches = EMyEnum::BranchB;
     }
 }

It works perfectly, however when I tried to implement it as a “better for loop” like so:

// .h

UENUM(BlueprintType)
enum class EmultiExecutionHandler : uint8
{
	Loop_Body,
	Completed
};

UFUNCTION(BlueprintCallable, meta = (ExpandEnumAsExecs = handled, Category = "Utilities|Flow Control", DefaultToSelf, HideSelfPin, DisplayName = "MEH_Cfor", KeyWords = "m,me,meh,mehc,mehcf,mehcfo,mehcfor,cfor,for,loop"))
void mehCfor(int32 iterStart, int32& index, int32 comparison, int32 iterEnd, bool positive, int32 amount, EmultiExecutionHandler& handled);


// .cpp

void UMyBlueprintFunctionLibrary::mehCfor(int32 iterStart, int32& index, const int32 comparison, const int32 iterEnd, const bool positive, const int32 amount, EmultiExecutionHandler& handled)
{
	if(positive)
	{
		if(comparison == 0)
			for(iterStart; iterStart == iterEnd; iterStart += amount) {
				if(iterStart != iterEnd)
				{
					index = iterStart;
					handled = EmultiExecutionHandler::Loop_Body;
				}
				if(iterStart == iterEnd)
				{
					index = iterStart;
					handled = EmultiExecutionHandler::Completed;
				}
			}
		if(comparison == 1)
			for(iterStart; iterStart <= iterEnd; iterStart += amount) {
				if(iterStart > iterEnd)
				{
					index = iterStart;
					handled = EmultiExecutionHandler::Loop_Body;
				}
				else
				{
					index = iterStart;
					handled = EmultiExecutionHandler::Completed;
				}
			}
		if(comparison == 2)
			for(iterStart; iterStart >= iterEnd; iterStart += amount) {
				if(iterStart < iterEnd)
				{
					index = iterStart;
					handled = EmultiExecutionHandler::Loop_Body;
				}
				else
				{
					index = iterStart;
					handled = EmultiExecutionHandler::Completed;
				}
			}
		if(comparison == 3)
			for(iterStart; iterStart < iterEnd; iterStart += amount) {
				if(iterStart >= iterEnd)
				{
					index = iterStart;
					handled = EmultiExecutionHandler::Loop_Body;
				}
				else
				{
					index = iterStart;
					handled = EmultiExecutionHandler::Completed;
				}
			}
		if(comparison == 4)
			for(iterStart; iterStart > iterEnd; iterStart += amount) {
				if(iterStart <= iterEnd)
				{
					index = iterStart;
					handled = EmultiExecutionHandler::Loop_Body;
				}
				else
				{
					index = iterStart;
					handled = EmultiExecutionHandler::Completed;
				}
			}
		if(comparison == 5)
			for(iterStart; iterStart != iterEnd; iterStart += amount) {
				if(iterStart == iterEnd)
				{
					index = iterStart;
					handled = EmultiExecutionHandler::Loop_Body;
				}
				else
				{
					index = iterStart;
					handled = EmultiExecutionHandler::Completed;
				}
			}
	}
	else
	{
		if(comparison == 0)
			for(iterStart; iterStart == iterEnd; iterStart -= amount) {
				if(iterStart != iterEnd)
				{
					index = iterStart;
					handled = EmultiExecutionHandler::Loop_Body;
				}
				else
				{
					index = iterStart;
					handled = EmultiExecutionHandler::Completed;
				}
			}
		if(comparison == 1)
			for(iterStart; iterStart <= iterEnd; iterStart -= amount) {
				if(iterStart > iterEnd)
				{
					index = iterStart;
					handled = EmultiExecutionHandler::Loop_Body;
				}
				else
				{
					index = iterStart;
					handled = EmultiExecutionHandler::Completed;
				}
			}
		if(comparison == 2)
			for(iterStart; iterStart >= iterEnd; iterStart -= amount) {
				if(iterStart < iterEnd)
				{
					index = iterStart;
					handled = EmultiExecutionHandler::Loop_Body;
				}
				else
				{
					index = iterStart;
					handled = EmultiExecutionHandler::Completed;
				}
			}
		if(comparison == 3)
			for(iterStart; iterStart < iterEnd; iterStart -= amount) {
				if(iterStart >= iterEnd)
				{
					index = iterStart;
					handled = EmultiExecutionHandler::Loop_Body;
				}
				else
				{
					index = iterStart;
					handled = EmultiExecutionHandler::Completed;
				}
			}
		if(comparison == 4)
			for(iterStart; iterStart > iterEnd; iterStart -= amount) {
				if(iterStart <= iterEnd)
				{
					index = iterStart;
					handled = EmultiExecutionHandler::Loop_Body;
				}
				else
				{
					index = iterStart;
					handled = EmultiExecutionHandler::Completed;
				}
			}
		if(comparison == 5)
			for(iterStart; iterStart != iterEnd; iterStart -= amount) {
				if(iterStart == iterEnd)
				{
					index = iterStart;
					handled = EmultiExecutionHandler::Loop_Body;
				}
				else
				{
					index = iterStart;
					handled = EmultiExecutionHandler::Completed;
				}
			}
	}
}

It seems to either loop always on zero if zero is within the range, or it never resolves to “handled = EmultiExecutionHandler::Loop_Body;” and instead always returns with “handled = EmultiExecutionHandler::Completed;” even when used like the standard for loop.

Any help much appreciated!

2

The issue that you’ve encountered is because functions are only ever evaluated once. Even when they have multiple exec outs like your first example, the best a function can do is choose one to activate and then be done. They have no way to to be re-executed and choose a different output.

If you look at the macro used for loops, you’ll notice that they involve a physical loop in the exec at some point to return control back to the loop after the body has been completed. You just can’t do that from within a single function.

That’s the bad news. The good news is that there is a C++ solution should you be so inclined and that is Custom K2 Nodes. There’s two flavors of them, the easier one basically allows you to create node macros from C++ and do all sorts of amazing things. I built a For-Each node that worked for Maps (the container, not the asset) which was basically impossible to do from the blueprint macro editor.

Early this year I wrote a tutorial Improving UE4 Blueprint Usability with Custom Nodes that tried to explain most of the knowledge I had gleaned since the existing docs and tutorials were basically non-existent.

I would be curious to know what you feel needs to be improved with the for-loop. It’s never really struck me as a node that has any real problems.

3

Thank you so much for the quick, informative reply!

Unfortunately I am in a bit of a time crunch right now, and I’ve found a different way to accomplish what I want, but in a short while I will have more time to go over what you’ve written regarding K2 nodes, because I believe it will be a more elegant solution.
As far as I know there is no way to have the default blueprint node for loop handle decrementing, which is what I need in this case.

Thanks to your comment I did just realize that I can copy the blueprint for loop macro and just edit it, that is probably the easiest solution in my case!