pytorch/torch/csrc/autograd/utils/lambda_post_hook.h

#pragma once

#include <torch/csrc/autograd/function_hook.h>
#include <torch/csrc/dynamo/compiled_autograd.h>

namespace torch::autograd::utils {

// Turns lambda into a torch::autograd::FunctionPostHook.
class LambdaPostHook : public torch::autograd::FunctionPostHook {
  using variable_list = std::vector<torch::autograd::Variable>;
  using fn_type =
      std::function<variable_list(const variable_list&, const variable_list&)>;
  using compiled_fn_type = std::function<void(CompiledNodeArgs&)>;

 public:
  // The lambda function takes as arguments the outputs and inputs of the
  // autograd function and can modify the outputs of the autograd function by
  // returning a new output if needed.
  /* implicit */ LambdaPostHook(fn_type fn) : fn_(std::move(fn)) {}

  LambdaPostHook(fn_type fn, compiled_fn_type compiled_fn)
      : fn_(std::move(fn)), compiled_fn_(std::move(compiled_fn)) {}

  variable_list operator()(
      const variable_list& outputs,
      const variable_list& inputs) override {
    return fn_(outputs, inputs);
  }

  void compiled_args(CompiledNodeArgs& args) override {}

 protected:
  std::function<variable_list(const variable_list&, const variable_list&)> fn_;
  compiled_fn_type compiled_fn_{};
};

} // namespace torch::autograd::utils