My cursorrules for elixir coding styles

elixir-coding-guidelines.mdc

When writing Elixir code, perfer the following style guidlines:

1. Elixir developers tend to create many small functions in their modules. I DO NOT LIKE THIS. Instead create functions that fully capture a conceptual task, even if it makes that function longer. A good rule of thumb is, if a private function is only called once within a module, it should've been inlined.


For example:

DON'T DO THIS:

```elixir
defmodule SomeModule do
    def some_public_function do
        x = some_private_function
        x + 1
    end

    defp some_private_function do
        72 / 2
    end
end
```

Instead, perfer to inline single use private functions:

```elixir
defmodule SomeModule do
    def some_public_function do
        x = 72 / 2
        x + 1
    end
end
```


2. DO NOT ADD UNNECESSARY CODE COMMENTS. Code should generally be self evident. I am a senior developer, I assure you I can understand the code you produce. Only add comments if it's not obvious what's going on, or if it's because of some edge case that isn't obvious.


3. Question Intermediate Layers, Ensure every layer of abstraction (like services) provides tangible value by hiding significant complexity. Wrapper modules just add unnecessary indirection and make the code more confusing to read.

Good Implementation:

```elixir

# Controller calls context directly
defmodule MyAppWeb.UserController do
  use MyAppWeb, :controller

  alias MyApp.Accounts

  def show(conn, %{"id" => id}) do
    user = Accounts.get_user!(id)
    render(conn, :show, user: user)
  end
end

# Context handles DB interaction
defmodule MyApp.Accounts do
  alias MyApp.Repo
  alias MyApp.Accounts.User

  def get_user!(id), do: Repo.get!(User, id)
end
```

Bad Implementation:

```elixir

# Controller calls a 'service'
defmodule MyAppWeb.UserController do
  use MyAppWeb, :controller

  alias MyApp.Users.UserService

  def show(conn, %{"id" => id}) do
    user = UserService.find_user_by_id(id)
    render(conn, :show, user: user)
  end
end

# Service just calls the context (Adds little value)
defmodule MyApp.Users.UserService do
  alias MyApp.Accounts

  def find_user_by_id(id) do
    Accounts.get_user!(id) # Just a pass-through
  end
end

# Context (Same as above)
defmodule MyApp.Accounts do
  alias MyApp.Repo
  alias MyApp.Accounts.User

  def get_user!(id), do: Repo.get!(User, id)
end
```