apache/beam · error

unsupported type for clone

Error message

unsupported type for clone: %v

What it means

reflectx.ShallowClone shallowly copies maps, slices, pointers and structs, but cannot meaningfully clone arrays, channels, interfaces, funcs, or the Invalid kind. The library panics for these types because a shallow copy would either be impossible or semantically wrong.

Solutions

1. Avoid storing func/chan/array/interface values in objects passed to ShallowClone, or wrap them in a cloneable struct.
2. Handle these kinds yourself before calling ShallowClone and pass only cloneable parts.
3. Ensure the reflect.Value is valid (not zero-valued) before cloning.

Example fix

// before
clone := reflectx.ShallowClone(reflect.ValueOf(someFunc)) // panics
// after
if v.Kind() == reflect.Func {
    clone = v // funcs are shared, not cloned
} else {
    clone = reflectx.ShallowClone(v)
}

switch v.Kind() {
case reflect.Array, reflect.Chan, reflect.Interface, reflect.Func, reflect.Invalid:
    return fmt.Errorf("cannot shallow-clone kind %v", v.Kind())
}

func cloneable(v reflect.Value) bool {
    switch v.Kind() {
    case reflect.Array, reflect.Chan, reflect.Interface, reflect.Func, reflect.Invalid:
        return false
    }
    return true
}

func safeClone(v reflect.Value) (out any, err error) {
    defer func() {
        if r := recover(); r != nil {
            err = fmt.Errorf("ShallowClone failed: %v", r)
        }
    }()
    return reflectx.ShallowClone(v), nil
}

When it happens

Trigger: Calling ShallowClone on a value whose kind is Array, Chan, Interface, Func, or Invalid — e.g. cloning a graph component that wraps a function value or an uninitialized (zero reflect.Value).

Common situations: Beam pipeline cloning helpers (shallowClonePipeline, ShallowClonePTransform) encountering a component field of func/interface/array kind; cloning a nil-valued reflect.Value.

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

• bad decode
• bad encode
• bad return type for
• base map cannot be nil
• beam.RegisterSchemaProvider: unsupported type kind for…

AI-assisted analysis of apache/beam@12126d8942 (2026-09-13). Data as JSON: /api/errors/63359aa3ae771521. Report an issue: GitHub.

Appendix: source

Thrown at sdks/go/pkg/beam/core/util/reflectx/util.go:58

		for i := 0; i < size; i++ {
			ret.Index(i).Set(val.Index(i))
		}
		return ret.Interface()

	case reflect.Map:
		if val.IsNil() {
			return reflect.Zero(t).Interface() // don't allocate for zero values
		}

		ret := reflect.MakeMapWithSize(t, val.Len())
		keys := val.MapKeys()
		for _, key := range keys {
			ret.SetMapIndex(key, val.MapIndex(key))
		}
		return ret.Interface()

	case reflect.Array, reflect.Chan, reflect.Interface, reflect.Func, reflect.Invalid:
		panic(fmt.Sprintf("unsupported type for clone: %v", t))

	default:
		return v
	}
}

// UpdateMap merges two maps of type map[K]*V, with the second overwriting values
// into the first (and mutating it). If the overwriting value is nil, the key is
// deleted.
func UpdateMap(base, updates any) {
	if updates == nil {
		return // ok: nop
	}
	if base == nil {
		panic("base map cannot be nil")
	}

	m := reflect.ValueOf(base)

View on GitHub (pinned to 12126d8942)