Shared Common Constants/Errors Across the Application

I’m also interested in hearing answers to this, especially for options that don’t spread compile time dependencies far and wide.

I had replied to your old post and I’m reposting my reply but with a few additions.

For many projects, I’ve often needed to use constants/enums. So I made a lib for it: SimpleEnum.

I’ll let you read the thread for more details, but to sum up:

• Enums can be used in guards
• There are no dependencies, as with EctoEnum for example.
• the introspection system makes it easy to connect SimpleEnum to other libs

Here is an example from the documentation:

iex> defmodule MyEnums do
...>   import SimpleEnum, only: [defenum: 2]
...>
...>   defenum :color, [:blue, :green, :red]
...>   defenum :day, monday: "MON", tuesday: "TUE", wednesday: "WED"
...> end

iex> require MyEnums

iex> MyEnums.color(:blue)
0
iex> MyEnums.color(0)
:blue
iex> MyEnums.day(:monday)
"MON"
iex> MyEnums.day("MON")
:monday

Thank you @ImNotAVirus ,
I would like to explore macros.

To be fair I’d just do this:

defmodule MyApp.UnixErrors do
  defmacro __using__(_opts) do
    quote do
      @bad_argument :badarg
      @invalid :einval
    end
  end
end

defmodule MyApp.UserModule1 do
  use MyApp.UnixErrors

  def hello(), do: @bad_argument
end

This too is some level of compile-time dependencies but they are flat, there are no cycles or deep graphs involved.

able to match them in guards and clauses?

Have you tried?

yes. I have to assign to temporary variables.And also cant have capital letters

defmodule Nat.Constants do
  @moduledoc false

  defmacro __using__(_) do
    quote do
      @st1 "urn:schemas-upnp-org:device:InternetGatewayDevice:1"
      @igd_device_upnp1 "urn:schemas-upnp-org:device:InternetGatewayDevice:1"
      @wan_device_upnp1 "urn:schemas-upnp-org:device:WANDevice:1"
      # @supported_protocols [Upnpv1, Upnpv2, PMP]

      @discover_timeout 5_000
      # :inet.parse_address('239.255.255.250')
      @multicast_ip {239, 255, 255, 250}
      @multicast_port 1900
      @mx_secs "3"
      @default_mapping_lifetime 7200
      @nat_initial_ms 200
      @default_attempts 3

      @st2 "urn:schemas-upnp-org:device:InternetGatewayDevice:2"
      @igd_device_upnp2 "urn:schemas-upnp-org:device:InternetGatewayDevice:2"
      @wan_device_upnp2 "urn:schemas-upnp-org:device:WANDevice:2"

      require Logger

      @nat_tries 3
      @nat_initial_ms 250
      @lifetime 3600

      @pmp_port 5351
    end
  end
end

Why not? For example these:

…are basically atoms.

image1376×290 62.4 KB

Also cant use them in the match and clauses.

Ah, you mean the module attributes can’t start with a capital letter. Can’t help you there, but I don’t see why would that be a hard requirement for you either.