Hi folks!

With the new release of Elixir 1.18, I would like to enforce pattern-matching by struct in our projects to take advantage of the type inference. To do so, I’m working on a Credo check and I would like feedback.

The rule will do the following:

Pattern-matching by an atom key of a map:

# not preferred
def get_role(%{role: role}) do # if the map keys are atoms it should be a Struct.
  role
end

Pattern-matching by struct

# preferred
def get_role(%User{role: role}) do
  role
end

# preferred
def get_role(user = %User{}) do
  user.role
end

I’ve found that there are cases where there are maps with atom keys and they don’t have to be structs, like in the props of the LiveView Components, or the Phoenix Controllers, but I think it is worth having this check and disable it for those cases, or cheat the rule moving the pattern matching inside the body of the function like for this case:

def update(%{param_1: param_1, param_2: param_2}, socket) do
  ...
end

doing:

def update(params, socket) do
  %{param_1: param_1, param_2: param_2} = params
  ...
end

Do you think it would make sense? Would you find it useful enough to add it to Credo?