Hi Everybody ;-),

Based on my understanding the proper Elixir way is to implement functions that return :ok or :error instead of raise exception. And then if there is a need you can implement a function with the same name + exclamation mark that you can use when you’re sure that the code should work and therefore if it doesn’t you want raise in that function to terminate the app (or process).

Recently I found myself in situation where I wanted to implement a lot of functions without and with exclamation mark.

Example:

defmodule MySuperCool.BigModule do
  def do_something(some_input, some_number) when is_map(some_input) and is_integer(some_number) do
    # stupid example
    case some_input do
      %{valid: true} -> {:ok, some_number}
      _ -> :error
    end
  end

  def do_something!(some_input, some_number) when is_map(some_input) and is_integer(some_number) do
    case do_something(some_input, some_number) do
      :error -> raise ArithmeticError
      {:ok, out} -> out
    end
  end

I’m looking at the code realizing that I have a lot of functions like do_something! with case that returns / raise exception. In other words I’m repeating the same code again and again…

So I tried to create a helper and rewrite it like this:

defmodule MySuperCool.SomeHelpers do
  def raise_error_or_return_value_in_tuple(result, exception \\ UndefinedFunctionError, exception_opts \\ [])
      when is_atom(exception) and is_list(exception_opts) do
    case result do
      :error -> raise exception, exception_opts
      {:ok, value} -> value
    end
  end
end

defmodule MySuperCool.BigModule do
  import MySuperCool.SomeHelpers, only: [raise_error_or_return_value_in_tuple: 3]

  # same as above

  def do_something!(some_input, some_number) when is_map(some_input) and is_integer(some_number) do
    some_input
    |> do_something(some_number)
    |> raise_error_or_return_value_in_tuple(ArithmeticError)
  end
end

And as you can see I “simplified” 4 lines of case statement into 3 lines some_input |> function |> raise_or_return.

In my view the simplification doesn’t really simplify it…

Could you please tell me should I just continue with case statements in every question mark function?

Thank you.

Kind regards,

Ben