12 — Diagnostics And Validation¶

Message Levels¶

FFuzzyDiagnostic has a Severity, text, and, if applicable, a RuleIndex.

Level	Meaning
`Info`	Useful information with no problem
`Warning`	The computation completed, but a fallback was used or something was skipped
`Error`	The system can't be considered correctly evaluated

ToString() and the Blueprint node Fuzzy Diagnostic To String return ready-to-display text like Error: unknown set (rule 3).

Data Asset Validation¶

UFuzzySystemAsset::IsDataValid is integrated into Unreal's standard content validation. Errors and warnings appear in the Message Log during content validation. In code and Blueprint, use Validate System.

Load Preset performs validation before changing the asset. Save To JSON also doesn't export a system with errors.

Common Errors¶

Invalid Range¶

Max must exceed Min, and both bounds must be finite. Fix the range before tuning the shapes.

Duplicate or Invalid Name¶

Variable and set names must be valid identifiers. Don't use spaces, hyphens, or the same name for an input and an output. Names are matched without regard to case, so Low and low on one variable count as a duplicate.

Reserved keywords (IF, IS, NOT, AND, OR, THEN, WITH) pass this check but cannot be referenced from a rule. If a rule fails with "Expected a variable name but found 'Or'", the problem is the variable's name, not the rule.

Unknown Variable or Set in a Rule¶

Check the spelling of authored names — case doesn't matter, but every other character does. The premise must reference an input, the consequence an output.

Mixed AND and OR¶

A single rule doesn't support both connectives. Split the logic into several rules.

No Rule for an Output¶

Add at least one rule whose consequence writes to every output you need.

No Rule Fired¶

This is a runtime warning, raised by every defuzzification method. The system returns the midpoint of the output range. Check the gaps between input sets and the scenario on the Inference tab.

Partial Preview¶

The editor can show results for rules that compiled successfully even when other rules have errors. Such a result is marked as a partial preview. It's needed for diagnostics, but bSuccess remains false.

Runtime Check¶

const FFuzzyInferenceResult Result = FuzzyLogic->Evaluate();
if (!Result.bSuccess)
{
    for (const FFuzzyDiagnostic& Diagnostic : Result.Diagnostics)
    {
        UE_LOG(LogTemp, Warning, TEXT("%s"), *Diagnostic.ToString());
    }
    return;
}

If the system's structure is known and validated during authoring, you don't need a separate validation every frame. The component caches the compilation.

What to Check Before Release¶

all Data Assets pass content validation;
edge and mid-range inputs have been checked in Inference;
every output has rules;
there are no unexpected fallback warnings;
JSON presets round-trip correctly;
game code checks bSuccess when the system could be external or variable.