⚡ How to auto-format functions without parentheses

Notes

Have you ever wondered how Phoenix and Ecto have functions whose arguments the Elixir formatter doesn’t automatically wrap with parentheses?

For example, look at Ecto.Schema’s field functions:

schema "users" do
  field :name, :string
end

How is it that mix format doesn’t turn field :name, :string into field(:name, :string)?

Or take Phoenix routes:

live "/users", UserLive

How is it that mix format doesn’t change that to live("/users", UserLive)?

Those functions act like a domain-specific language, and it’s nice when they can be formatted without parentheses.

Did you know you can do that for functions in your own project? 😲

All you have to do is declare which functions (along with their arities) you want to format without parentheses in your .formatter.exs file!

[
  import_deps: [:ecto, :ecto_sql, :phoenix],
  # ... other stuff

  locals_without_parens: [echo: 2]
]

We’ve just added our echo/2 function to locals_without_parens so it doesn’t get wrapped in parentheses when the Elixir formatter runs!

Go ahead and write echo/2 without parens to your heart’s content!

- echo("hello", "world")
+ echo "hello", "world"