econf

Loads environment variables into your structs in one shot.

econf allows to override struct fields with environment variables easily. This is useful to build up applications that optionally overrides some configuration with environment variables. Here is the basic usage:

use econf::LoadEnv;

#[derive(Debug, LoadEnv)]
struct A {
    x: bool,
    y: u64,
}

fn main() {
    let a = A {
        x: true,
        y: 42,
    };
    println!("Before: {:?}", a);

    let a = econf::load(a, "PREFIX");
    println!("After:  {:?}", a);
}

$ ./app
Before: A { x: true, y: 42 }
After:  A { x: true, y: 42 }

$ PREFIX_X=false ./app
Before: A { x: true, y: 42 }
After:  A { x: false, y: 42 }

In this example,

• PREFIX_X is loaded to x
• PREFIX_Y is loaded to y

Why econf?

There are some existing crates that provide similar features but econf is unique in the following ways:

• Supports nesting: Supports nested structs in an intutive manner with a little constraint.
• Supports compound types: Supports tuple, Vec, HashMap and various types.
• Supplemental: Loads supplementally into existing variables in the code without changing the original logic.
• Contributor friendly: Simple code base. Comprehensible with a little study on basic macro usage.

Supported types

• Boolean: bool
• Integer: isize, usize, i8, i16,i32,i64,i128, u8,u16,u32,u64,u128
• String: char, String
• Float: f32, f64
• Network: IpAddr,Ipv4Addr,Ipv6Addr,SocketAddr,SocketAddrV4,SocketAddrV6
• Non-zero types: NonZeroI128,NonZeroI16,NonZeroI32,NonZeroI64,NonZeroI8,NonZeroIsize,NonZeroU128, NonZeroU16,NonZeroU32,NonZeroU64,NonZeroU8, NonZeroUsize
• File system: PathBuf
• Containers: Vec, HashSet, HashMap, Option, BTreeMap, BTreeSet, BinaryHeap, LinkedList, VecDeque
  • Containers are parsed as YAML format. See the tests.

Skipping fields

Fields that do not implement LoadEnv or simply should not be loaded by econf can be skipped by adding the #[econf(skip)] helper attribute:

#[derive(LoadEnv)]
struct A {
    x: bool,
    #[econf(skip)]
    y: u64, // will not be loaded by econf
}

License: MIT