kai_feldhoff

Call callback-function inside Behaviour-Module

In my current project I have a rather complex data-tranfsformation. Additionally there are several flavors fo ths trqansormation that share a lot of behaviour.

Is therea any other may to call a callback-function inside a bahaviour apart from passing the module-name of the callback-module like this?

defmodule MyBehaviour do
  @callback specific_handling(data :: term) :: term

  @callback very_specific_handling(data :: term) :: term

  defmacro __using__(_opts) do
    quote do
      @behaviour MyBehaviour

      alias MyBehaviour

      def initiate_processing(data) do
        MyBehaviour.process_data(data, __MODULE__)
      end
    end
  end

  def process_data(data, callback_module) do
    data
    |> do_stuff_with_data(callback_module)
    # and other calls to behaviour-functions
    |> callback_module.specific_handling()
  end

  defp do_stuff_with_data(data, callback_module) do
    data
    # and other calls to behaviour-functions
    |> do_specific_stuff(callback_module)
  end

  defp do_specific_stuff(data, callback_module) do
    data
    # and other calls to behaviour-functions
    |> callback_module.very_specific_handling()
  end
end

defmodule DataHandler11 do
  use MyBehaviour

  def specific_handling(data) do
    # do specific stuff with data
    data
  end

  def very_specific_handling(data) do
    # do specific stuff with data
    data
  end
end

defmodule DataHandler12 do
  use MyBehaviour

  def specific_handling(data) do
    # do specific stuff with data
    data
  end

  def very_specific_handling(data) do
    # do specific stuff with data
    data
  end
end

data = nil
handler = 1

case handler do
  1 -> DataHandler11.initiate_processing(data)
  2 -> DataHandler12.initiate_processing(data)
end

4 comments

#behaviours #callbacks

0 236 4

2024-11-13 19:30:21 UTC

Marked As Solved

dimitarvp

I would give you a thumbs up during code review on a PR like this – it’s all good.

If you are worried about this approach then the only other practice that’s more “micro” would be to only pass function references – but then you would be losing the compiler warnings if a contract is violated i.e. if the function has the same arity but accepts different kinds of arguments.

So IMO callback modules are the right solution here.

Post #3

Last Post!

al2o3cr

Another option would be to generate all the required code into the module that says use. This replaces threading callback_module everywhere by local calls:

defmodule MyBehaviour do
  @callback specific_handling(data :: term) :: term

  @callback very_specific_handling(data :: term) :: term

  defmacro __using__(_opts) do
    quote do
      @behaviour MyBehaviour

      alias MyBehaviour

      def initiate_processing(data) do
        data
        |> do_stuff_with_data()
        # and other calls to behaviour-functions
        |> specific_handling()
      end

      defp do_stuff_with_data(data) do
        data
        # and other calls to behaviour-functions
        |> do_specific_stuff()
      end

      defp do_specific_stuff(data) do
        data
        # and other calls to behaviour-functions
        |> very_specific_handling()
      end
    end
  end
end

defmodule DataHandler11 do
  use MyBehaviour

  def specific_handling(data) do
    # do specific stuff with data
    data
  end

  def very_specific_handling(data) do
    # do specific stuff with data
    data
  end
end

defmodule DataHandler12 do
  use MyBehaviour

  def specific_handling(data) do
    # do specific stuff with data
    data
  end

  def very_specific_handling(data) do
    # do specific stuff with data
    data
  end
end

data = nil
handler = 1

case handler do
  1 -> DataHandler11.initiate_processing(data)
  2 -> DataHandler12.initiate_processing(data)
end

This has a cost: the code output by __using__ is compiled over again for every module that calls it, versus only being compiled once when MyBehaviour is compiled.

Post #5