bortzmeyer

bortzmeyer

Conditional dependencies in mix.exs

I have a program which can provide different services, depending on its run-time configuration (through a configuration file or command-line options). Some of the services, but not all, depend on external libraries, such as HTTPoison, so I add in my mix.exs:

      {:httpoison, "~> 1.8"} 

But I would like to avoid this dependency (HTTPoison brings a lot of other libraries) if not necessary. How to make it conditional, and allow the program to know if it has been included or not, so it can produce a proper error message if the user tries to activate the service, without having the library?

I’ve read this StackOverflow post, which seems to be about a different problem, and this Elixir Forum discussion which was inconclusive.

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mayel

mayel

Actually, re-reading the docs it looks like in your case (if this is a top level app) it would always be included, so maybe a similar approach but using only to specify [:dev, :test] if the dep is disabled, and [:dev, :test, :prod] if it should be enabled?

moogle19

moogle19

Yes, of course. I forgot to mention that.

You can do something like this:

defmodule SomeModule do
  if Mix.target() == :your_target_no do
    def some_function do
      HTTPoison.get("elixirforum.com")
    end
  else
    def some_function do
      # Do something without HTTPoison
    end
  end
end

Not sure if that suits your needs and how complex the httpoison integration is in your app.

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