A Quick Style Guide Update for Elixir 1.11

Elixir 1.11 is coming and bringing new data constructors compile checks that will change a little bit the safest way to write Elixir code. The good news is: it is for the best. The update will make your structs attribute access less verbose and straightforward.

Before Elixir 1.11, if we have a struct like this:

defmodule User do
  defstruct :last_access
end

And if we use this way:

user = %User{}
user.last_acess

We’ll have a runtime error. Didn’t notice the typo? No? Don’t worry, neither Elixir compiler would catch. That error last_acess key doesn’t exist error would only pop up during runtime. That’s why my previous suggestions of Elixir code style was to write code like this:

user = %User{}
%User{last_acess: last_access} = user

This time, the Elixir compiler will notice the not existing key and fail early, before any code run. I suggested this approach, but personally, I never loved it. It’s more verbose, less straightforward, and a duplication of information. You need to tell the compiler twice that you’re working the %User{} struct. But at the same time, we’re helping the compiler catch silly mistakes as early as possible. But these days are over with the release of Elixir 1.11 smarter compile check for data constructors. Now, if you write that first version:

user = %User{}
user.last_acess

The Elixir 1.11 will detect that last_acess doesn’t exist and fail during compilation phase. With this new feature, here are my new preferable styles:

# (dynamic, preferable for test)
user.id

# (static, preferable for lib)
%User{} = user # tell compiler which struct you expect here
user.id # have fun with dot notation

# not preferred
def create_order!(item, user) do
  Repo.insert!(%Order{
    user_id: user.id,
    user_email: user.email,
    user_shipping_address_id: user.user_shipping_address_id,
    total_price: item.price,
    total_weight: item.weight,
    quantity: 1
  })
end

# preferred
# tell the compiler which structs you expect in your function signature
def create_order!(%Item{} = item, %User{} = user) do
  # have fun with dot notation
  Repo.insert!(%Order{
    user_id: user.id,
    user_email: user.email,
    user_shipping_address_id: user.user_shipping_address_id,
    total_price: item.price,
    total_weight: item.weight,
    quantity: 1
  })
end

That’s all! I’ve also updated my style guide post with the improved data constructors feature. I hope Elixir 1.11 helps you write beautiful code.

I know it’s have been a time since the last post. When the mid-spring arrived, I confess it was hard to stay at home and write after a long winter and quarantine isolation. In Estonia, the quarantine period was fast, something like 2-3 months, and we could back to “normal life” and enjoy mid-spring and summer. Now, the autumn is coming, the cases are increasing again, and probably soon, we’ll be stuck in quarantine again. Thanks to that, maybe I’ll write more. Stay safe!