private:
  struct ConcreteFunction {
    tensorflow::AbstractFunctionPtr trace;
    TaggedValue input_signature;
    TaggedValue output_signature;
  };
  tensorflow::StatusOr<ConcreteFunction> GetConcreteFunction(TaggedValue) const;
  std::vector<ConcreteFunction> concrete_fns_;
};

}  // namespace libtf
}  // namespace tf

  //  If status is not OK, returns nullptr. Otherwise, returns a
  //  tensorflow::cc::ConcreteFunction pointer. The lifetime of this pointer
  //  is bound to SavedModelAPI it was loaded from.
  ConcreteFunction* GetConcreteFunction(const std::string& function_path,
                                        Status* status);

  // Retrieve a function from the TF SavedModel via a SignatureDef key.
  //
  // Params:

StatusOr<TaggedValue> Function::Execute(AbstractContext* ctx,
                                        TaggedValue value) const {
  TF_RETURN_IF_ERROR(VerifySupportedArgs(value));
  TF_ASSIGN_OR_RETURN(auto concrete_fn, GetConcreteFunction(value));
  std::vector<AbstractTensorHandle*> args;
  Flatten(value, &args);
  std::vector<AbstractTensorHandle*> outs(
      GetFlatSize(concrete_fn.output_signature));
  TF_RETURN_IF_ERROR(