docs: def weld_merge_join(arrays_self, weld_types_self, arrays_other, weld_types_other,
                      how, is_on_sorted, is_on_unique, readable_text):
      """Applies merge-join on the arrays returning indices from each to keep in the resulting
  
      Parameters
      ----------
      arrays_self : list of (numpy.ndarray or WeldObject)
          Columns from the self DataFrame on which to join.
      weld_types_self : list of WeldType
          Corresponding Weld types.
      arrays_other : list of (numpy.ndarray or WeldObject)
          Columns from the other DataFrame on which to join.
      weld_types_other : list of WeldType
          Corresponding Weld types.
      how : {'inner', 'left', 'right'}
          Which kind of join to do.
      is_on_sorted : bool
          If we know that the on columns are already sorted, can employ faster algorithm.
      is_on_unique : bool
          If we know that the values are unique, can employ faster algorithm.
      readable_text : str
          Explanatory string to add in the Weld placeholder.
  
      Returns
      -------
      tuple of WeldObject
          Two columns of indices from the input arrays, indices of the rows from self and other that should be
          available in the resulting joined DataFrame.
  
      """
      assert is_on_unique
  
      weld_obj_vec_of_struct_self = weld_arrays_to_vec_of_struct(arrays_self, weld_types_self)
      weld_obj_vec_of_struct_other = weld_arrays_to_vec_of_struct(arrays_other, weld_types_other)
  
      weld_obj_join = _weld_merge_join(weld_obj_vec_of_struct_self,
                                       weld_obj_vec_of_struct_other,
                                       len(arrays_self),
                                       how,
                                       is_on_unique)
  
      intermediate_result = LazyStructOfVecResult(weld_obj_join, [WeldLong(), WeldLong()])
      dependency_name = Cache.cache_intermediate_result(intermediate_result, readable_text)
  
      weld_objects = extract_placeholder_weld_objects(dependency_name, 2, readable_text)
  
      return weld_objects