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Dependency inversion on Elixir using Ports and Adapters design pattern

Diogo Dourado on January 10, 2023

Introduction Dependency Inversion is a well-known software development principle, described by Robert C. Martin as the responsible of sy...
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Bruno Ribeiro •

Hey man, great article!! I always try to implement this pattern on my code. One thing that a make different, is that I use defdelegate on the port, I think that make the code more easy to understand. But thanks for the excellent article

defmodule MySystem.SmsNotificationPort do
  @moduledoc """
  Sends SMS to users using configured SMS adapter.
  """

  @callback notify(user :: User.t(), message :: String.t()) :: :ok | :error

  @adapter Application.get_env(:my_system, __MODULE__)

  defdelegate notify(user, message), to @adapter
end
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Juan Barrios •

Doesn't assigning it to @adapter make it a compiled variable, breaking the Application.put_env trick?

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Diogo Dourado •

Yes @03juan, didn't notice that

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Diego Camacho •

I think you're right, in this case we need to move to a private function instead

defp adapter, do: Application.get_env(:my_system, __MODULE__)

Doesn't it?

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Bruno Ribeiro •

Yep! You right! I already change this implementation, and now I use Application.get_env instead

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Diogo Dourado •

Great tip, Bruno! Thanks for the feedback

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Diego Camacho • • Edited

Hi Bruno,

I don't quite understand why the delegate or function call of the behavior should be made in the port, what's the porpuse?

It's because all the application use the MySystem.SmsNotificationPort.notify/2 function?

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Bruno Ribeiro •

Hey Diego!! How are you?

Well, I use the delegate on the port, because the port's idea is to be an interface. The only responsibility of the port is to call the correct adapter.

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Luiz Cezer •

Awesome content!

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Rakshan Shetty •

Paring this with mox for testing makes testing so much simpler

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Bruno Ribeiro • • Edited

Yep! I like to use with Hammox! It's a really good abstraction for the mox