What causes "A collection type" in stride3d/stride?

Inspect the struct type whose descriptor sets IsReference and fix the custom descriptor/factory so structs are not treated as references

stride3d/stride · error · QuantumConsistencyException

A collection type

Error message

A collection type

What it means

DefaultNodeBuilder.VisitObject throws QuantumConsistencyException when a node created from an object turns out to be a reference node while its descriptor type is a struct. Quantum expects struct-typed values to be boxed/plain value nodes, not reference nodes, so this signals an internal node-factory/type-descriptor inconsistency.

Solutions

Inspect the struct type whose descriptor sets IsReference and fix the custom descriptor/factory so structs are not treated as references
Update Stride.Core packages so Quantum and TypeDescriptor versions match
If the type should be a class, change the model so the descriptor's type is not a struct
Catch QuantumConsistencyException during Build and log the offending type to identify the misregistered descriptor

Example fix

// before: custom factory returns a reference node for a struct
public override IObjectNode CreateObjectNode(...) => new ObjectNode(..., isReference: true);
// after: let the default factory box value types
var content = descriptor.Type.IsValueType
    ? NodeFactory.CreateBoxedNode(this, rootGuid, obj, descriptor)
    : NodeFactory.CreateObjectNode(this, rootGuid, obj, descriptor);

Defensive patterns

Strategy: validation

Validate before calling

if (descriptor.Type.IsValueType && descriptor.IsReference) throw new InvalidOperationException($"{descriptor.Type} is a struct marked as reference");

Type guard

bool IsValidStructNode(ITypeDescriptor d) => !(d.Type.IsValueType && d.IsReference);

Try / catch

try { builder.Build(obj); } catch (QuantumConsistencyException ex) { logger.LogError(ex, "Quantum inconsistency for {Type}", ex.Object?.GetType()); }

Prevention

Never override node factories to mark structs as references
Keep Stride.Core.Quantum and Stride.Core.Assemblies versions in sync
Test graph builds over all struct types in your model

When it happens

Trigger: Visiting an object whose TypeDescriptor reports IsValueType (struct) but NodeFactory.CreateBoxedNode/CreateObjectNode produces a node with IsReference=true, e.g. a type whose descriptor is inconsistent (custom ITypeDescriptor, mismatched metadata) during Build of a NodeContainer.

Common situations: Custom type descriptors or node factories overriding default behavior; struct types registered or resolved through descriptors that mark them as reference types; library version mismatch where IsReference detection changed.

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

Related errors

AI-assisted analysis of stride3d/stride@96fad776d2 (2026-09-14). Data as JSON: /api/errors/6fbb237ef970178a. Report an issue: GitHub.

Appendix: source

Thrown at sources/presentation/Stride.Core.Quantum/DefaultNodeBuilder.cs:70

        return rootNode!;
    }

    /// <inheritdoc/>
    public override void VisitObject(object obj, ObjectDescriptor descriptor, bool visitMembers)
    {
        ITypeDescriptor currentDescriptor = descriptor;

        bool isRootNode = contextStack.Count == 0;
        if (isRootNode)
        {
            // If we're visiting a value type as "object" we need to use a special "boxed" node.
            var content = descriptor.Type.IsValueType ? NodeFactory.CreateBoxedNode(this, rootGuid, obj, descriptor)
                : NodeFactory.CreateObjectNode(this, rootGuid, obj, descriptor);

            currentDescriptor = content.Descriptor;
            rootNode = (IInitializingObjectNode)content;
            if (content.IsReference && currentDescriptor.Type.IsStruct())
                throw new QuantumConsistencyException("A collection type", "A structure type", rootNode);

            PushContextNode(rootNode);
        }

        if (!PrimitiveTypeFilter.IsPrimitiveType(currentDescriptor.Type))
        {
            base.VisitObject(obj, descriptor, true);
        }

        if (isRootNode)
        {
            PopContextNode();
            rootNode!.Seal();
        }
    }

    /// <inheritdoc/>
    public override void VisitCollection(IEnumerable collection, CollectionDescriptor descriptor)

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