BoundaryML/baml · error

unexpected type for last log: %T %v

Error message

unexpected type for last log: %T %v

What it means

Thrown by Collector.Last() at rawobjects_collector.go:90 when CallMethod("last") returns a non-nil value that does not implement the FunctionLog interface. The runtime returned an object of the wrong kind for 'last'.

Source

Thrown at engine/language_client_go/pkg/rawobjects_collector.go:90

		functionLogs[i] = cast
	}

	return functionLogs, nil
}

func (c *collector) Last() (FunctionLog, error) {
	result, err := raw_objects.CallMethod(c, "last", nil)
	if err != nil {
		return nil, fmt.Errorf("failed to get last log: %w", err)
	}

	if result == nil {
		return nil, nil
	}

	log, ok := result.(FunctionLog)
	if !ok {
		return nil, fmt.Errorf("unexpected type for last log: %T %v", result, result)
	}

	return log, nil
}

func (c *collector) Id(functionId string) (FunctionLog, error) {
	result, err := raw_objects.CallMethod(c, "id", map[string]any{
		"id": functionId,
	})
	if err != nil {
		return nil, fmt.Errorf("failed to get log by id: %w", err)
	}

	log, ok := result.(FunctionLog)
	if !ok {
		return nil, fmt.Errorf("unexpected type for log by id: %T", result)
	}

View on GitHub (pinned to bd85ce9dee)

Solutions

1. Align Go client and native runtime versions; rebuild.
2. Check the printed %T to identify the leaked concrete type.
3. File an upstream bug with the type name if versions match.

Example fix

// before
log, _ := collector.Last()
// after
log, err := collector.Last()
if err != nil {
	return fmt.Errorf("collector.Last() type error: %w", err)
}

if collector == nil { return errors.New("collector not initialized") }

func asLog(v any) (baml.FunctionLog, bool) {
	l, ok := v.(baml.FunctionLog)
	return l, ok
}

log, err := collector.Last()
if err != nil {
	if strings.Contains(err.Error(), "unexpected type") { /* version mismatch — escalate */ }
	return err
}

When it happens

Trigger: collector.Last() where the native runtime returns a raw object wrapped as something other than a FunctionLog (version mismatch or wrong object registration).

Common situations: Go bindings/native runtime version skew; runtime returning an internal object type not mapped to FunctionLog in the Go layer.

Understand the failure class

Background: Type mismatch errors: IllegalArgumentException, TypeError and type guards across 150 open-source libraries — this error's family across 150 libraries.

Related errors

• unexpected type for logs: %T
• unexpected type in logs: %T
• unexpected type for log by id: %T
• unexpected type for clear result: %T
• failed to get usage: %w

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/6440b4c14ebb0804. Report an issue: GitHub.