Loading & saving

dotcfg separates “there is no config yet” from “the config is broken.” You decide whether a missing file is normal, an error, or a reason to create defaults.

Optional: load()

Use this when your application can run without a saved config. A missing file becomes Ok(None); I/O and parse failures still return errors.

let config: Option<AppConfig> = cfg.load()?;

if let Some(config) = config {
    println!("Loaded {}", config.theme);
}

Required: load_or_error()

Use this when the application must be configured before it can continue.

let config: AppConfig = cfg.load_or_error()?;

Create defaults: load_or_default()

This requires your type to implement Default. If the file is missing, dotcfg constructs T::default(), saves it, and returns that value.

#[derive(Serialize, Deserialize, Default)]
struct AppConfig {
    theme: String,
}

let config: AppConfig = cfg.load_or_default()?;

Save a complete config

save() serializes your struct in the selected format. The config directory is created automatically when it does not exist.

let config = AppConfig {
    theme: "dark".into(),
};

cfg.save(&config)?;