temporalio/temporal · error

Can't deep copy value of type %s: %v

Error message

Can't deep copy value of type %s: %v

What it means

deepCopyValue handles only the concrete kinds the dynamicconfig default-copy supports (structs, maps, slices, pointers to those, basic scalars). Any other value — e.g. a func, chan, or unhandled composite — reaches the default branch and panics. Like error 613, it fires from static initializers when a setting default contains an unsupported type.

Source

Thrown at common/dynamicconfig/deepcopy.go:76

				return reflect.ValueOf(time.Time{})
			}
			// nolint:forbidigo // this will be triggered from a static initializer before it can be triggered from production code
			panic(fmt.Sprintf("Can't deep copy non-zero time.Time: %v", v.Interface()))
		}
		nv := reflect.New(v.Type()).Elem()
		for i := range v.Type().NumField() {
			nv.Field(i).Set(deepCopyValue(v.Field(i)))
		}
		return nv
	case reflect.Interface, reflect.Func, reflect.Chan:
		// only nil values of any other reference types allowed!
		if v.IsNil() {
			return v
		}
		fallthrough
	default:
		// nolint:forbidigo // this will be triggered from a static initializer before it can be triggered from production code
		panic(fmt.Sprintf("Can't deep copy value of type %s: %v", v.Type(), v))
	}
}

View on GitHub (pinned to bde624efd1)

Solutions

1. Remove or retype the unsupported field in the setting's default value
2. Add a case in deepCopyValue for the needed reflect.Kind if genuinely required
3. Flatten the default struct so it only contains scalars, strings, slices, maps, and nested structs

Example fix

// before
Setting{Callback: func() {}}
// after
Setting{} // handle callbacks outside the config default value

// reject chan/func/unsafe kinds in defaults

When it happens

Trigger: Declaring a dynamicconfig setting whose default value contains a field/value of an unsupported type (func, chan, interface holding something exotic, unsafe pointer) which deepCopyValue recursively encounters.

Common situations: Adding a callback field to a config struct default; nesting a map with non-copyable values; upgrading a setting's struct with a new field of an unhandled type.

Related errors

• Can't deep copy non-zero time.Time: %v
• ConvertGradualChange can only be used with scalar types for
• dynamicconfig.New*Setting must only be called from static in
• duplicate registration of dynamic config key: %q
• unsupported error type: %v

AI-assisted analysis of temporalio/temporal@bde624efd1 (2026-09-01). Data as JSON: /api/errors/8e0fc1faeac54750. Report an issue: GitHub.