What causes "Unable to serialize scalar [{value}] not supported" in stride3d/stride?

Register a custom IYamlSerializable/serializer factory for the unsupported type.

stride3d/stride · error · YamlException

Unable to serialize scalar

Error message

Unable to serialize scalar [{value}] not supported

What it means

PrimitiveSerializer.ConvertTo throws this when serializing a value whose runtime type is not one of the primitives the serializer can emit as a YAML scalar. After the type switch, if no text representation was produced, it throws a YamlException without location info.

Solutions

Register a custom IYamlSerializable/serializer factory for the unsupported type.
Change the member type to a supported primitive or string.
Check which value type reached ConvertTo and extend the type switch (if owning a fork).
Verify the serializer factory selector routes the type to the correct serializer, not PrimitiveSerializer.

Example fix

// before
public MyCustomStruct Value { get; set; }
// after
public string Value { get; set; } // or register a custom serializer

Defensive patterns

Strategy: validation

Validate before calling

static bool IsYamlPrimitiveSupported(Type t) =>
    t.IsPrimitive || t.IsEnum || t == typeof(string) || t == typeof(decimal) || t == typeof(DateTime) || t == typeof(TimeSpan) || t == typeof(Guid);

Try / catch

try { serializer.Serialize(writer, graph); } catch (YamlException ex) { throw new NotSupportedException($"YAML serializer cannot encode value: {ex.Message}", ex); }

Prevention

Audit model members for custom structs/value types before enabling YAML serialization.
Register a custom IYamlSerializable for every non-primitive value type.
Keep models to primitives, strings, enums, and registered types.
Test serialization of every model type in unit tests.

When it happens

Trigger: Serializing an object graph containing a value type that falls through the switch (unsupported enum underlying type, custom struct, null-boxed odd value, or a type the schema routed to PrimitiveSerializer incorrectly).

Common situations: Adding a new custom value type to a model and serializing it without registering a serializer; schema misconfiguration routing a complex type to the primitive serializer; older/newer library versions where a TypeCode is not handled.

Understand the failure class

Background: UnsupportedOperationException and "is not supported" errors: when a library deliberately refuses a call — this error's family across 30 libraries.

Related errors

AI-assisted analysis of stride3d/stride@96fad776d2 (2026-09-14). Data as JSON: /api/errors/fe564ede541417d0. Report an issue: GitHub.

Appendix: source

Thrown at sources/core/Stride.Core.Yaml/Serialization/Serializers/PrimitiveSerializer.cs:270

                        break;
                    case TypeCode.Decimal:
                        text = AppendDecimalPoint(((decimal) value).ToString("G", CultureInfo.InvariantCulture), false);
                        break;
                    case TypeCode.DateTime:
                        text = ((DateTime) value).ToString("o", CultureInfo.InvariantCulture);
                        break;
                    default:
                        if (valueType == typeof(TimeSpan))
                        {
                            text = ((TimeSpan) value).ToString("G", CultureInfo.InvariantCulture);
                        }
                        break;
                }
            }

            if (text == null)
            {
                throw new YamlException($"Unable to serialize scalar [{value}] not supported");
            }

            return text;
        }
    }
}

View on GitHub (pinned to 96fad776d2)