Mahaul - Supercharge the environment variables usage in your Elixir app

LIGHTBULB
I get it now. Thanks!

Can you give some brief example of how such a dynamic pattern matching can work at compile time? Form what I can think of, the following will give you runtime errors without any compile time warnings.

defmodule Env do
  def get_env("VAR_1"), do: "..."
  def get_env("VAR_2"), do: "..."
end

defmodule SomeModule do
  def something() do
    Env.get_env("VAR_1") # works
    Env.get_env("VAR_2") # works
    Env.get_env("VAR_3") # runtime error with no compile time warnings
  end
end

vs

defmodule Env do
  use Mahaul,
    VAR_1: [type: :str],
    VAR_2: [type: :num]
end

defmodule SomeModule do
  def something() do
    Env.var_1() # works
    Env.var_2() # works
    Env.var_3() # compile time warnings for non-existing method call
  end
end

Thanks for clarifying as I had indeed misunderstood.

I’m still not sure I follow here though. This seems like with pattern matching you could hard code the strings for the env variables of interest and have the same sort of confidence. I can see that mahaul provides a single interface with the system env where you handle checking for the variables and providing defaults or handling errors rather than needing to do so everywhere you use the env variable in the application. Mahaul also seems to make it a lot easier to use different variables for different environments and to update them easily when the names of variables change between versions or something.

This sounds like a true win for me.

Well, the point of configuration is to use them in your code later, just as libraries use them and you can do that easily by calling get_env/3 or fetch_env/2, however taking in consideration the limitation of the configuration/compilation it seems that the only way to enforce something at compile-time is to make a custom module.

It would be great if such a functionality were to be introduced somewhere in the elixir internals so it could be used in all configurations.

I certainly use environment variables in my code beyond just config files. So even though the idea of macros in runtime.exs is certainly nice, I still want to be able to access those environment variables values independently in my code as needed. This is why a separately initialized module where I can see/configure all the environment variables used by my app in one glance, makes more sense to me from flexibility and ease of use standpoint.

Ah true, quite sad but it makes sense. Well at least for runtime.exs it would be nice to have the check.

You can only do that with Config.Provider implementations (e.g. runtime.exs), but that won’t be able to provide compile time configuration. The chicken/egg situation means config first then applications, because you need to be able to configure said applications. So applications cannot be available or be used in config/config.exs.

The usage of environment variables is not in question here, the thing that I try to point out is that I would like to use this library, however I would like the environment variable specification defined in the config.exs directly, not with a separate module.

In my opinion there is no reason to create your own wrappers over the config way of storing those values, however a check of the environment value type is a great thing.

To make my point cleaner, I will illustrate an dev.exs example:

import Config
# Import or use your module here
import MagicMacro

config :my_app, MyApp.Endpoint,
    http: [port: safe_env(PORT: [type: :port, default: "4000"])]

@D4no0 IMHO I don’t think elixir configs are limiting in any way, if anything I’ve found it to be very well thought and structured with perfect balance of standardization vs flexibility. I’ve rarely come across anything so flexible and feature complete that’s baked in as part of the core language feature, as elixir configs.

I feel it’s important to understand there’s a difference between app configuration and environment variables and they are not a replacement to each other rather environment variables compliment your app’s configurability. You can choose to configure your app with static values or environment variables, the choice is totally up to you. The fact that elixir configs lets you achieve this in a feature complete way, in itself is wonderful to me.

Oh I see, this is a limitation of elixir configs. It would be nice to also have a macro or sigil to define a typed/checked environment variable directly into config, without generating the function at compile-time of course, as I hate having to look into 10 different files to find the actual config.