Custom C++ UStruct or UClass Used Inside a Math Expression Node

Development Programming & Scripting Blueprint
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1

Is there a method of defining a UStruct or UClass such that you can reference them inside blueprint math expression nodes? Or does the math expression node not utilize reflection in this way?

2

I guess the answer is no.

3

I know this question is a few months old but hopefully this will be beneficial to someone.

tl:dr

Give your UFUNCTION a CompactNodeTitle of the operator or function name that you want to use, e.g.

UFUNCTION(BlueprintPure, meta = (CompactNodeTitle = "/", Keywords = "/ divide quotient"), Category = "Math|Vector3")

Alternatively, use DisplayName instead:

UFUNCTION(BlueprintPure, meta = (DisplayName = "*", Keywords = "* multiply times product"), Category = "Math|Vector3")

How it works

I also wanted to use functions and mathematical operators on a custom USTRUCT. So I looked into the Unreal codebase. As of 4.12.5 Editor/BlueprintGraph/Private/K2Node_MathExpression.cpp is what you’re after. Around line 804 we see:

if (TestFunction->HasMetaData(FBlueprintMetadata::MD_CompactNodeTitle))
{
	FunctionName = TestFunction->GetMetaData(FBlueprintMetadata::MD_CompactNodeTitle);
}
else if (TestFunction->HasMetaData(FBlueprintMetadata::MD_DisplayName))
{
	FunctionName = TestFunction->GetMetaData(FBlueprintMetadata::MD_DisplayName);
}
Add(FunctionName, TestFunction);

So, it’ll use CompactNodeTitle if present, otherwise it’ll use DisplayName. In the above examples, this allowed me to write *(V1, V2), and also the infix style V1 * V2 (I assume because it’s a recognised operator, see line 2172 onward of K2Node_MathExpression.cpp).

My concern was mainly with mathematical operators but the functional style should work for any function name. See also Runtime/Engine/Classes/Kismet/KismetMathLibrary.h for how unreal declares mathematical operations for its built-in types.