BoundaryML/baml · error

unexpected type for logs: %T

Error message

unexpected type for logs: %T

What it means

Thrown by Collector.Logs() in engine/language_client_go/pkg/rawobjects_collector.go:63 when the underlying FFI CallMethod("logs") returns a value that is not a []raw_objects.RawPointer slice. The BAML Go client unmarshals raw C++ collector objects into typed Go values; if the runtime returns something unexpected, this internal type-assertion guard fires. It almost always indicates an FFI/version mismatch or a corrupted raw object rather than user error.

Source

Thrown at engine/language_client_go/pkg/rawobjects_collector.go:63

	}

	name, ok := result.(string)
	if !ok {
		return "", fmt.Errorf("unexpected type for name: %T", result)
	}

	return name, nil
}

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

	logs, ok := result.([]raw_objects.RawPointer)
	if !ok {
		return nil, fmt.Errorf("unexpected type for logs: %T", result)
	}

	functionLogs := make([]FunctionLog, len(logs))
	for i, log := range logs {
		cast, ok := log.(FunctionLog)
		if !ok {
			return nil, fmt.Errorf("unexpected type in logs: %T", log)
		}
		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)

View on GitHub (pinned to bd85ce9dee)

Solutions

1. Ensure the Go baml client version matches the native BAML runtime/binary version; rebuild and re-link.
2. Upgrade github.com/boundaryml/baml Go package and regenerate any BAML client code.
3. If reproducible, file a bug with the %T value printed in the message.

Example fix

// before
logs, err := collector.Logs()
// after
logs, err := collector.Logs()
if err != nil {
	var te *baml.TypeMismatchError
	if errors.As(err, &te) { /* runtime/client version mismatch: reinstall matching baml binaries */ }
}

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

func safeLogs(c baml.Collector) ([]baml.FunctionLog, bool) {
	logs, err := c.Logs()
	if err != nil { return nil, false }
	return logs, true
}

logs, err := collector.Logs()
if err != nil {
	if strings.Contains(err.Error(), "unexpected type") {
		// Go client / native runtime version mismatch: fail fast with guidance
	}
	return err
}

When it happens

Trigger: Calling collector.Logs() when the BAML runtime's 'logs' method returns a non-slice raw object — typically from a version mismatch between the Go client and the native BAML runtime, or a raw object registered under the wrong object type.

Common situations: Mixed-version baml-go bindings and native binaries; upgrading the BAML runtime without rebuilding the Go client; corrupted Collector handle after runtime restart.

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 in logs: %T
• unexpected type for last log: %T %v
• 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/7b02270ea745d885. Report an issue: GitHub.