Lib.rs

Crate for macro-based configuration management.

Description

This crate and it's sister micronfig_macros combine to provide the config macro, which allows the developer to define all configuration variables required by an application in a single place and have them expanded to static references of the desired types.

micronfig::config! {
	DATABASE_URI,
	APPLICATION_NAME: String,
	MAX_CONCURRENT_USERS: String > u64,
	SHOWN_ALERT?,
}

Examples

Strings configuration

To define configuration variables returning a string, create a config block and list their names separated by commas ,:

micronfig::config! {
	VARIABLE_A,
	VARIABLE_B,
	VARIABLE_C,
	PATH,
}

To access them, call their name as if it was a function:

#
#
// These will all return `&'static str` values.
println!("{}", VARIABLE_A());
println!("{}", VARIABLE_B());
println!("{}", VARIABLE_C());
println!("{}", PATH());

Note

Both the config block and variables defined in it are lazily initialized on first call.

The first time one of these functions is called, configuration files will be parsed, and the first time each is called, its value is retrieved and stored.

Required and optional variables

By default, configuration variables are all required, causing a [panic] if their value is missing the first time their function is called.

Configuration variables can be marked as [Option]al by suffixing a question mark ? to their name, making them return a &'static Option instead:

micronfig::config! {
	VARIABLE_REQUIRED,
	VARIABLE_OPTIONAL?,
}

Conversions

All variables are read from their source as strings; therefore, the following explicit syntax for defining them is supported:

micronfig::config! {
	VARIABLE_A: String,
	VARIABLE_B: String,
	VARIABLE_C: String,
}

Strings are not the best option for most situations, so the crate makes use of some traits to allow their conversion to different types:

The syntax for conversion is as follows:

use std::net::SocketAddr;

micronfig::config! {
 	// use FromStr to parse the String as an isize
	REQUIRED_SIGNED: String > isize,
 	// use FromStr to parse the String as a SocketAddr
 	REQUIRED_SOCKETADDR: String > SocketAddr,
	// use From to convert the String to... another String
	REQUIRED_STRING: String -> String,
	// use TryFrom to convert the String to another String
 	// (there aren't many types in std to make valid examples from!)
	REQUIRED_TRYSTRING: String => String,
	// the conversion will not be performed for missing optional variables
   	OPTIONAL_UNSIGNED?: String > usize,
}

Custom types can be used as well:

struct Duplicator {
	copy_a: String,
	copy_b: String,
}

impl From<String> for Duplicator {
	fn from(value: String) -> Self {
        Self {
			copy_a: value.clone(),
			copy_b: value
		}
    }
}

micronfig::config! {
	MY_CUSTOM_TYPE: String -> Duplicator,
}

Conversions can be chained too:

struct ChatId(u64);

impl From<u64> for ChatId {
	fn from(value: u64) -> Self {
        Self(value)
    }
}

micronfig::config! {
	// First parse the string as an u64 with FromStr, then convert it to a ChatId with From.
	RESPOND_TO_MESSAGES_IN: String > u64 -> ChatId,
}

Crate features

Value sources

The crate supports retrieving values from various different sources depending on the needs of the application.

The sources can be toggled on and off via crate features, and are listed in the following table in order of retrieval priority, where the topmost one is the first source that is checked, and the following ones are checked only if no value is detected in the ones above.

By default, all of them are enabled.