Specify: Comfortable, Explicit, Multi-Layered Configuration Specifications - v0.7

[Qqwy]

@OvermindDL1

Took a bit to read it, looks like a fantastic start!

So a few starter questions:

1. You can make arbitrary configuration loaders and handlers?

Yes . The Confy.Provider protocol can be implemented by anything you want.

@OvermindDL1

2. What about one that pulls from a database on some kind of update message so it updates the configurations in real time, is there a way to tell something like a gen_server built on this to accept this new configuration (say like changing the pool size in a database pool)?

Currently, not. I am planning to, in a way similar to what Vapor does, offer the possibility to spin up a background ‘configuration change watcher’ process that will trigger a message when the configuration changes at runtime. (Unfortunately for most providers this will require polling).

The GenServer could then decide to switch over to the new configuration, stop and start a new version of itself with the new configuration, or potentially even recompile a module if, for optimization reasons, the compilation process itself is affected by the configuration.

@OvermindDL1

3. How do you differentiate between the different stages of configurations? I.E. Compile-time, Load-Time, and Run-Time (dynamic)?

Confy treats them in the same way. Configuration is only ever loaded when YourConfigModule.load(options \\ []) is called. At that time, Confy will look through the sources that you have configured, and for every field, decide which source has the highest priority.

So if you have the following configuration:

defmodule MyRepo do
  import Confy
  defconfig sources: [Confy.Providers.MixEnv, Confy.Providers.Process] do
    field :endpoint, :string, default: "localhost"
    field :port, :integer, default: 8086
  end
end

then when calling MyRepo.load(options) it will:

• Take the default values of :endpoint and :port
• Possibly override them by a value set in the Application configuration.
• Possibly override them by a value set in the current process’ process dictionary.
• Possibly override them by a value set in the overrides: key of the options passed to MyRepo.load.

---

The idea is that you call YourConfigModule.load once (or infrequently) and keep the struct it returns around in e.g. your GenServer state.This means that parsing of individual config fields has to be done only once, and that you end up with an explicit representation of the configuration. Also, because you end up with ‘just’ a struct, the logic that uses this configuration can be completely stateless and might be easier to test.