Lib.rs

This is a helper library which is dedicated to make extracting value from environment variables easy.

How To Import

add below line to cargo.toml which is in your project

nb-from-env = "*"

Usage

use nb_from_env::{FromEnv, FromEnvDerive}


#[derive(FromEnvDerive)]
struct MyServerConfig {
    log_level: Option<String>,
    listen_address: String,
    max_conns: i32,
    is_debug: bool,
}

fn main() {
    dotenv::dotenv().ok();
    let config = MyServerConfig::from_env();
    ...
}

Support Data Types

almost all of primitive types in rust are supported, include:

• String
• i8
• i16
• i32
• i64
• i128
• u8
• u16
• u32
• u64
• u128
• usize
• isize
• bool
• f32
• f64
• Option<T: FromEnv>

you can also implement FromEnv for your type

Environment Variable Name

If not specified, all environment variables name is the upper-case of field name:

#[derive(FromEnvDerive)]
struct MyConfig {
    my_var: String  // this will search for MY_VAR in environment varialbes
}

but you can use #[env_var] tag to specify which environment variable is related to the field:

#[derive(FromEnvDerive)]
struct MyConfig {
    #[env_var(THE_REAL_NAME)] // this will search for THE_REAL_NAME in environment variables
    my_var: String
}

Default Value

You can specify default value for non-existing environment variable by #[env_default] tag:

struct MyConfig {
    #[env_default("my default value")] // if MY_VAR not exists, "my default value" will assign to my_var
    my_var: String
}

note that, the type of default value must be string, value will be convert to correspond type in from_env function

Optional Type Field

When environment variable whic you expected does not exist, from_env will panic if correspond field is not optional(i.e Option<T>). Optional field will be None if environment variable is not exists