Crate envfig

Envfig

A flexible and type-safe system for defining, documenting, and validating environment variables.

The EnvVarDef type provides a builder-style interface to define environment variables with optional default values, human-friendly metadata (title, description, example), and custom validation logic.

It supports loading required or optional variables using EnvVarDef::load and EnvVarDef::load_option, and will return rich error types when parsing or validation fails.

Example

use std::{env, str::FromStr};

use envfig::{EnvVarDef, LoadError, validator::Validator};

// A simple validator that ensures the value is greater than zero
struct Positive;

impl Validator<i32> for Positive {
    type Err = String;

    fn validate(
        self,
        val: i32,
    ) -> Result<i32, Self::Err> {
        if val > 0 {
            Ok(val)
        } else {
            Err("Value must be positive".into())
        }
    }
}

// Set an environment variable
unsafe {
    env::set_var("APP_PORT", "8080");
}

let port = EnvVarDef::new("APP_PORT")
    .with_title("Application Port")
    .with_description("The port the application listens on")
    .with_example(8080)
    .with_validator(Positive)
    .load()
    .unwrap();

Features

• Type-safe parsing from environment variables.
• Optional default value fallback.
• Full metadata support (title, description, example).
• Custom validation support via the Validator trait.
• Granular error types via LoadError.

Traits

• Validator<T> is required to perform validation of environment variable values.

Modules

validator

Module contains a Validator trait definition along with the some implementation’s of this trait.

Structs

EnvVarDef

Represents the definition of an environment variable, including its name, optional default value, metadata (title, description, example), and optional validation logic.

Enums

LoadError

Errors which could occure during the EnvVarDef::load method