code: def get_field(expr, field):
      
      weld_obj = WeldObject(encoder_, decoder_)
  
      struct_var = weld_obj.update(expr)
      if isinstance(expr, WeldObject):
          struct_var = expr.obj_id
          weld_obj.dependencies[struct_var] = expr
  
      weld_template = """
        %(struct)s.$%(field)s
      """
  
      weld_obj.weld_code = weld_template % {"struct":struct_var,
                                            "field":field}
      return weld_obj
docs: Fetch a field from a struct expr