CommutativeAssociativeBinaryOperator and const reference parameters

Development Programming & Scripting Blueprint
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1

Have been experiencing an issue where using const reference parameters in a function marked with the CommutativeAssociativeBinaryOperator metadata property declared like this

UFUNCTION(BlueprintPure, meta = (DisplayName = "SpecialStruct + SpecialStruct", CompactNodeTitle = "+", Keywords = "+ add plus", CommutativeAssociativeBinaryOperator = "true"), Category = "Math|Special")
	static void AddSpecialStructs(const FSpecialStruct& A, const FSpecialStruct& B, FSpecialStruct& Result);

has been producing the following error :

LogOutputDevice:Error: Ensure condition failed: InputType == Pin->PinType [File:D:\Build++UE4+Release-4.15+Compile\Sync\Engine\Source\Editor\BlueprintGraph\Private\K2Node_CommutativeAssociativeBinaryOperator.cpp] [Line: 128]

This happens whenever a blueprint with this operator is opened or that operator is placed within a blueprint.

A cursory look at the differences between the pin types are the same only that the InputType is const and a reference and Pin->PinType is not. Any subsequent pins beyond the two default pins that are added using the small ‘+’ in the lower right corner of the node also appear to use the small diamond input pin style usually reserved for references.

2

JackMorgan, did you fix it? 4.19 has the same behavior…

UFUNCTION(BlueprintPure, Category = "FABRIK|test", meta = (DisplayName = "AppendIntArrays", CommutativeAssociativeBinaryOperator = "true"))
static TArray<int32> BP_Append_IntArray(const TArray<int32>& A, const TArray<int32>& B)
{
	TArray<int32> out =A;
	out.Append(B);
	return out;
}

[2018.04.29-06.19.57:292][355]LogBlueprintUserMessages:
[NewBlueprint1_C_0] 1.0
[2018.04.29-06.19.57:296][355]LogSlate: Took 0.000187 seconds to synchronously
load lazily loaded font
‘…/…/…/Engine/Content/Slate/Fonts/Roboto-BoldCondensed.ttf’
(158K)
[2018.04.29-06.19.59:848][555]LogOutputDevice:
Error: Ensure condition failed:
InputType == Pin->PinType
[File:D:\Build++UE4+Release-4.19+Compile\Sync\Engine\Source\Editor\BlueprintGraph\Private\K2Node_CommutativeAssociativeBinaryOperator.cpp]
[Line: 127]

[2018.04.29-06.19.59:848][555]LogStats: FDebug::EnsureFailed - 0.000 s
UE4Editor.exe has triggered a
breakpoint.

if you continue the work then the function works as expected

3

I can confirm that this still behaves as described in 4.20; I’m seeing the same thing. K2Node_CommutativeAssociativeBinaryOperator.cpp:127:
ensure(InputType == Pin->PinType);

The Input type is the same as the pin type. However the PinType, named “ReturnValue” is non-const as it is a new value. The fault also occurs if the return pin is a value and the parameter pins are a reference:
/** Returns the maximum value of A and B */
UFUNCTION(BlueprintPure, meta=(DisplayName = “Max (BigInt)”, CompactNodeTitle = “MAX”, CommutativeAssociativeBinaryOperator = “true”), Category=“Math|BigInt”)
static const FBigInt Max(const FBigInt& A, const FBigInt& B);

4

I can confirm that this still behaves as described in 4.20; I’m seeing the same thing. K2Node_CommutativeAssociativeBinaryOperator.cpp:127:
ensure(InputType == Pin->PinType);

The Input type is the same as the pin type. However the PinType, named “ReturnValue” is non-const as it is a new value. The fault also occurs if the return pin is a value and the parameter pins are a reference:
/** Returns the maximum value of A and B */
UFUNCTION(BlueprintPure, meta=(DisplayName = “Max (BigInt)”, CompactNodeTitle = “MAX”, CommutativeAssociativeBinaryOperator = “true”), Category=“Math|BigInt”)
static const FBigInt Max(const FBigInt& A, const FBigInt& B);