code: func goodFunc(typ reflect.Type) bool {
  	// We allow functions with 1 result or 2 results where the second is an error.
  	switch {
  	case typ.NumOut() == 1:
  		return true
  	case typ.NumOut() == 2 && typ.Out(1) == errorType:
  		return true
  	}
  	return false
  }
docs: // goodFunc checks that the function or method has the right result signature.