template <typename Gradient, typename BackwardFunction, typename TapeTensor>
void ForwardAccumulator<Gradient, BackwardFunction, TapeTensor>::DeleteGradient(
    int64_t tensor_id) {
  auto existing = accumulated_gradients_.find(tensor_id);
  if (existing != accumulated_gradients_.end()) {
    vspace_.DeleteGradient(existing->second);
    accumulated_gradients_.erase(existing);
  }
}

  // Converts a Gradient to a TapeTensor.
  TapeTensor TapeTensorFromGradient(AbstractTensorHandle* g) const override;

  void MarkAsResult(AbstractTensorHandle* gradient) const override;

  void DeleteGradient(AbstractTensorHandle* gradient) const override;

 private:
  // The context where the aggregation op `Add` is to be created.
  AbstractContext* ctx_;
};