parameters: (self, function_spec, input_args_with_spec,
                   input_kwargs_with_spec, class_instance, **kwargs)
docstring: Initializes a cache key.
  
          Args:
              functions_spec(FunctionSpec): a FunctionSpec instance of decorated function.
              input_args_with_spec(list[InputSpec]): actual input args with some arguments replaced by InputSpec.
              input_kwargs_with_spec(list[{string:InputSpec}]): actual input kwargs with some arguments replaced by InputSpec.
              class_instance(object): a instance of class `Layer`.
              **kwargs(dict): manage other arguments used for better scalability
docstring_summary: Initializes a cache key.
docstring_tokens: Initializes a cache key .
function: def __init__(self, function_spec, input_args_with_spec,
                   input_kwargs_with_spec, class_instance, **kwargs):
          """
          Initializes a cache key.
  
          Args:
              functions_spec(FunctionSpec): a FunctionSpec instance of decorated function.
              input_args_with_spec(list[InputSpec]): actual input args with some arguments replaced by InputSpec.
              input_kwargs_with_spec(list[{string:InputSpec}]): actual input kwargs with some arguments replaced by InputSpec.
              class_instance(object): a instance of class `Layer`.
              **kwargs(dict): manage other arguments used for better scalability
          """
          self.function_spec = function_spec
          self.input_args_with_spec = input_args_with_spec
          self.input_kwargs_with_spec = input_kwargs_with_spec
          self.class_instance = class_instance
          # NOTE: `kwargs` is usually not considered as basic member for `__hash__`
          self.kwargs = kwargs
          self._spec_names_id = _hash_spec_names(input_args_with_spec,
                                                 input_kwargs_with_spec)
function_tokens: def __init__ ( self , function_spec , input_args_with_spec , input_kwargs_with_spec , class_instance , * * kwargs ) : self . function_spec = function_spec self . input_args_with_spec = input_args_with_spec self . input_kwargs_with_spec = input_kwargs_with_spec self . class_instance = class_instance # NOTE: `kwargs` is usually not considered as basic member for `__hash__` self . kwargs = kwargs self . _spec_names_id = _hash_spec_names ( input_args_with_spec , input_kwargs_with_spec )