Sooner or later, that application you're writing will need to be configured. At the very least, you'll need a way to adjust inputs without editing source code. Wouldn't it be nice to have a reasonable configuration system from the start?
The best way to configure your app will depend on the environment in which you're using the software, and the requirements of the project, all of which will change over time. Ideally, we'd start out with a system that had the flexibility to pull our configuration from a number of input sources:
For a language that is often refered to as a low-level "systems" language, Rust allows for some very ergonomic abstractions. We can implement a type-safe configuration system with a minimal amount of imperative code, letting the third-party crates handle the mechanical details. Let's walk through a new project...