code: def wrap_once(self, LayoutClass, *args, **kwargs):
          
          def wrap_object_once(layout_object, j):
              if not isinstance(layout_object, LayoutClass):
                  layout_object.fields[j] = self.wrapped_object(
                      LayoutClass, layout_object.fields[j], *args, **kwargs
                  )
  
          self.pre_map(wrap_object_once)
docs: Wraps every layout object pointed in `self.slice` under a `LayoutClass` instance with
          `args` and `kwargs` passed, unless layout object's parent is already a subclass of
          `LayoutClass`.