Config

The config module reads environment variables. It is intended for use at application startup, not inside request handlers.

Reading values

import mistweaver/config

// Option(String) — None if unset
let maybe_secret = config.get("APP_SECRET")

// String with a default fallback
let secret = config.get_or("APP_SECRET", "dev-secret-change-me")

// String — panics at boot if unset
let secret = config.require("APP_SECRET_KEY_BASE")

Pattern: fail fast at boot

Use config.require for values that the application cannot start without. A clear panic at boot is better than a confusing runtime error during a request:

pub fn main() {
  let secret = config.require("APP_SECRET_KEY_BASE")
  let db_url = config.require("DATABASE_URL")
  ...
}

Pattern: dev defaults

Use config.get_or for values that have sensible development defaults:

let secret = config.get_or("APP_SECRET_KEY_BASE", "dev-only-secret")
let port   = config.get_or("PORT", "4000") |> int.parse |> result.unwrap(4000)