// instead allow ForwardAccumulator some control over the current tape set
    // (so it can deactivate itself and activate its GradientTape). Currently
    // that is managed by the language binding and would require relatively
    // messy callbacks.
    call_state_.top().backward_tape->RecordOperation(
        op_type, output_tensors, input_tensor_id, input_dtypes,

  // Release any underlying resources, including the interface object.
  //
  // WARNING: The destructor of this class is marked as protected to disallow
  // clients from directly destroying this object since it may manage it's own
  // lifetime through ref counting. Thus this must be allocated on the heap and
  // clients MUST call Release() in order to destroy an instance of this class.
  virtual void Release() = 0;

  /// implemented by a filesystem registered to handle the `fs://` scheme.
  ///
  /// A new `char*` buffer must be allocated by this method. Core TensorFlow
  /// manages the lifetime of the buffer after the call. Thus, all callers of
  /// this method must take ownership of the returned pointer.
  ///
  /// The implementation should clean up paths, including but not limited to,