Elixir Terminology: Parameters vs Attributes

This post was originally written for my old ElixirFocus blog, and transfer here after its closure.

I’ve written about being explicit and mindful about programming terminology before and today we’ll look at another specific Elixir terminology example: parameters vs attributes.

If you create a new Phoenix app and use the generators to stub out a simple CRUD experience you will no doubt observe web controller functions like:

defmodule HelloWeb.PostController do
  # ...
  def create(conn, %{"post" => post_params}) do
    case Blog.create_post(post_params) do
      # ...
    end  end
end

And internal schema module functions like:

defmodule Hello.Blog.Post do
  # ...
  def changeset(post, attrs) do
    post
    |> cast(attrs, [:body, :word_count])
    |> validate_required([:body, :word_count])
  end
end

Observing function argument names like post_params (short for parameters) and attr (short for attributes) how do we reconcile those naming choices?

Parameters

When we say “parameters” we are usually talking about data coming into the system from external actors, like a user POST-ing data from a web form or an API accepting a request. Parameters are generally considered unsafe. Since the contents are dynamic they will almost always be made from maps using string keys to avoid the known runtime capacity limitations of :atom keys.

Attributes

When we say “attributes” we are usually talking about internal Elixir structures. When a function accepts a simple map argument labeled attr, as seen in our example, I think we can lean on the definition for attribute which says, “a quality, character, or characteristic ascribed to someone or something”.

While attr is a community norm for incoming function arguments, there is an unfortunate overlap with some official Elixir terminology. A module attribute is how we describe those at sign (@) declarations like @email below.

defmodule ContactSupport do
  @email "mike@mikezornek.com"
end

Short post today, but hopefully some helpful context about some community naming norms.