config

config.load[T] fills a struct with string, int, and bool fields from CLI arguments, environment variables, TOML files, and field defaults, in that order.

import config

struct ServerConfig {
    host  string @[default: 'localhost']
    port  int    @[default: '8080']
    debug bool   @[default: 'false']
}

fn main() {
    cfg := config.load[ServerConfig](cli: ['--port=9090'], env_prefix: 'APP_')!
    println(cfg.port) // 9090
}

CLI accepts --field=value, --field value, and bare --field as true. Underscores in field names may be written as dashes; the last CLI value wins across both spellings. Environment keys default to the prefix plus uppercase field name; @[env: 'NAME'] uses that exact key instead. The first TOML file containing a matching top-level key wins. Unreadable or invalid files return an error.

@[default: 'value'] supplies a fallback. Missing fields return an error; @[required] provides a required-key diagnostic. Empty strings are provided values. Decimal integers must fit V's signed 32-bit int; invalid values and overflow return errors. Booleans accept true, 1, yes, false, 0, and no, ignoring case. Other field types are unsupported.

fn load[T](opts LoadOptions) !T

load fills a struct from the configured sources. Each field takes its value from the first source that provides it:

1. cli: --field or --field-with-dashes, as --k=v or --k v
2. env: @[env: 'NAME'], else env_prefix + UPPER(field)
3. files: the TOML top-level key matching the field name
4. @[default: '...']

A field with no value and no default is an error, as is a field marked @[required]. Supported field types are string, int and bool; anything else is a compile error. Example:

struct ServerConfig {
    host  string @[env: 'HOST'; default: 'localhost']
    port  int    @[default: '8080']
    debug bool   @[default: 'false']
    token string @[required]
}

cfg := config.load[ServerConfig](cli: os.args[1..], env_prefix: 'APP_',
    files: ['app.toml', '/etc/app.toml'])!

struct LoadOptions {
pub:
	// cli are raw arguments, e.g. os.args[1..]; understands --key=value,
	// --key value, and bare --flag (meaning "true")
	cli []string
	// env_prefix is prepended to UPPER(field) names, e.g. 'APP_'
	env_prefix string
	// files are TOML documents read in order; unreadable paths are errors
	files []string
}

LoadOptions selects where configuration values come from, in precedence order: cli, then env, then files (first hit wins), then @[default].