Crate derive_environment

A Rust library for modifying structs via environment variables.

Unlike envy, this does not create a new object. It is used to reconfigure an existing structure (after having parsed it from a config file, for example).

Ignored fields

If a certain field should not be configurable via environment variables, mark it with #[env(ignore)].

Examples

Creating a config structure:

use derive_environment::FromEnv;

#[derive(Default, FromEnv)]
pub struct Config {
    // ...
}

// Creates a base configuration struct to add on to.
// Normally this would be created using `serde` from a config file.
let mut config = Config::default();
// Names the struct "MY_CONFIG", which acts as a prefix.
config.with_env("MY_CONFIG").unwrap();

---

Nesting fields:

use derive_environment::FromEnv;

#[derive(FromEnv)]
struct ServerConfig {
    port: u16,
}

#[derive(FromEnv)]
pub struct Config {
    server: ServerConfig,
}

Generates:

• MY_CONFIG_SERVER_PORT

---

Vector of Nested fields:

use derive_environment::FromEnv;

// `Vec`'s `FromEnv` implementation requires `Default`.
#[derive(Default, FromEnv)]
struct ServerConfig {
    port: u16,
}

#[derive(FromEnv)]
pub struct Config {
    servers: Vec<ServerConfig>,
}

Generates:

• MY_CONFIG_SERVER_0_PORT

Macros

• impl_using_from_str
  Automatically implements FromEnv using the type’s FromStr implementation.

Enums

• FromEnvError
  Errors generated when populating a structure from the environment.

Traits

• FromEnv
  Denotes a type that may be read from an environment variable.

Type Aliases

• Result
  The result of FromEnv::with_env.

Derive Macros

• FromEnv
  Generates a load_environment() function that will populate each field from environment variables.