I have a library (MyLib) that I use for part of another app’s functionality (MyApp). I’d like to add some conditional code (an Ecto schema definition) to one of the library’s modules only if MyApp has a particular config that points to one of MyApp’s modules (also an Ecto schema). I was hoping to ca…

Nothing wrong with runtime configuration. But that doesn’t help you if you’re doing meta programming at compile time. Think of Ecto as a good example. Although all the Repo code lives in Ecto, you are required to create your own MyApp.Repo module and use Ecto.Repo in it with the appropriate config…

You may need to use Code.ensure_compiled/1 to force compilation order if it isn’t being detected the way you want. The documentation notes that this is not a function you should commonly reach for. However forcing compilation order at compile time is one reasonable use.

This doesn’t seem to work for my use case, perhaps I using it incorrectly? My current implementation looks like this: MyLib.MyModule if Application.get_env(:my_lib, :some_config) do case Code.ensure_compiled(Application.get_env(:my_lib, :some_config)) do {:module, module} -> # do someth…

It would be helpful to know: What the result of Application.get_env(:my_lib, :some_config) is What the error return was (instead of ignoring it add it to the log message)

[image] kip: What the result of Application.get_env(:my_lib, :some_config) is Elixir.MyApp.ConfigModule [image] kip: What the error return was unavailable

Thanks. That return code pretty much says its compiled everything and that module wasn’t found. Just to be really sure, the module is actually defined as defmodule MyApp.ConfigModule not defmodule Elixir.MyApp.ConfigModule? Is :my_lib a dependency of the project? So that it will be compiled first,…

[image] kip: the module is actually defined as defmodule MyApp.ConfigModule not defmodule Elixir.MyApp.ConfigModule ? Yep. Is :my_lib a dependency of the project? [image] kip: Is :my_lib a dependency of the project? Yes, exactly. So when I compile the project (MyApp) I see ==> my_l…

Ah, I see. Compilation order is dependencies first, then the current project. Where current project is the one that has mix.exs in it when you did mix.compile. Dependencies are compiled first and they do not create a transitive association with the “current” project. Understandably so - libraries a…

The common pattern in Elixir to handle this kind of situation is to introduce a new module into the current project and then use the code from the dependency so you can create a relationship. This is what I do heavily in the ex_cldr libs for pretty much the same reason you have - conditional compila…

To explain additionally why conditional compilation in a dependency isn’t a good idea I should point out that the dependency could be used my multiple different consuming libraries in the same runtime environment and therefore unpredictable behaviour would ensue.

[image] kip: The common pattern in Elixir to handle this kind of situation is to introduce a new module into the current project I had a feeling that something like this would be the correct option. Otherwise the config is going to extremely unwieldy and redundant. I’m just not quite sure the…

Conditional code based on config

Questions & Help Questions

tfwright May 31, 2020, 7:17pm 5

Elixir.MyApp.ConfigModule

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