Generally, libraries shouldn’t rely on application env at all. A lot of libraries continue to use that pattern because it was popular in the early days of Elixir. But its a bad model and shouldn’t be copied. If your library needs to use processes, then users should be able to pass in arguments when they start the process in their supervisor. Redix is an excellent example of how to do this well.
There are exceptions to this rule. Sometimes it makes the most sense to provide a full-blown OTP Application. I typically do this because there’s nothing in the application to configure, the supervision hierarchy is complex, or if there’s no benefit to the user managing the lifecycle of the process.
Building a library that is re-usable without collisions is often much more difficult. But I think it pays off in the long run.
