envman 1.0.2

Rust crates to manage environment variables.
Documentation 
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# [EnvMan][docsrs]: Environments (variables) Manager

[![EnvMan on crates.io][cratesio-image]][cratesio]
[![EnvMan on docs.rs][docsrs-image]][docsrs]

[cratesio-image]: https://img.shields.io/crates/v/envman.svg
[cratesio]: https://crates.io/crates/envman
[docsrs-image]: https://docs.rs/envman/badge.svg
[docsrs]: https://docs.rs/envman

This crate adds a macro for easy management of environment variables.

If you would like to see more details, please see [these codes](https://github.com/moriyoshi-kasuga/envman/tree/main/envman/tests).

## Example

```rust
use envman::EnvMan;

unsafe {
  std::env::set_var("F0", "-1");
  std::env::set_var("f1", "1");
}

// The type of field can be set if FromStr is implemented
#[derive(EnvMan)]
struct Foo {
  f0: i32,
  #[envman(rename = "f1")]
  f_1: u8,
  #[envman(default = "default value".to_string())]
  f_n: String,
  f_o: Option<i32>,
  #[envman(default = 1, test = 2)]
  f_test: u8,
}

// If rename is not set, it will be an upper case
let foo = Foo::load().unwrap();
// This value is taken from “F0”.
let f0 = foo.f0;
// This value is taken from “f1”.
let f_1 = foo.f_1;
// This value is taken from “F_N” and if it is not set, it will be set to “default value”.
let f_n = foo.f_n;
// This value is taken from “F_O” and if it is not set, it will be set to None.
let f_o = foo.f_o;
// This value is taken from “F_TEST” and if it is not set, it will be set to 1.
// and if it under test, it will be set to 2.
let f_test = foo.f_test;
```

## Usecase

```rust
use std::{net::SocketAddr, sync::LazyLock};

use envman::EnvMan;

fn main() {
    // this unsafe block is necessary for test
    // and it is not necessary in production
    unsafe {
        std::env::set_var("JWT_SECRET", "secret");
    }

    // initialize
    let _ = &*ENVIRONMENTS;

    println!("API_URL: {}", ENVIRONMENTS.api_url);
}

pub static ENVIRONMENTS: LazyLock<Environments> = LazyLock::new(|| Environments::load().unwrap());

#[derive(EnvMan)]
pub struct Environments {
    #[envman(default = "127.0.0.1:8080", alltime_parse)]
    pub api_url: SocketAddr,
    #[envman(test = "secret".to_string())]
    pub jwt_secret: String,
}
```

## Field Attributes

- rename : `rename = "new name"` (default: upper case)
- parser: `parser = constants::default_parser` (default: FromStr::from_str)
  > parser type is `fn(&str) -> Result<T, E>` and `E` has impl `std::error::Error`
- group_test: (default: None)
  > if under test, use this value (Priority is first)
  - test: `test` Use Default::default()
  - test: `test = Default::default()` (put anything of expr)
- group_default: (default: None)
  > if not found in env, use this value
  > if a test exists and is under test, use the test
  - default: `default`
  - default: `default = Default::default()` (put anything of expr)
- alltime_parse: `alltime_parse` (default: false)
  > The normal default (and test) return value is the field type
  > if this is set, the return value is a string and the parser is used

## License

Licensed under

- [MIT license](https://github.com/moriyoshi-kasuga/envman/blob/main/LICENSE)