# serde-env-field
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This crate provides the `EnvField<T>` type capable of deserializing the `T` type
from a string with environment variables expanded.

During deserialization, the `EnvField` will try to deserialize the data as a string and expand all
the environment variables. After the expansion, the resulting string will be used
to construct the `T` value.
By default, the `EnvField` will construct the `T` value using the `FromStr` trait.
However, it is possible to make it use the `Deserialize` trait using the [UseDeserialize](https://docs.rs/serde-env-field/latest/serde_env_field/struct.UseDeserialize.html) marker.

If the supplied data was not a string, the `EnvField`
will attempt to deserialize the `T` type directly from the data.

The `EnvField` works nicely with `Option`, `Vec`, and `#[serde(default)]`.

Also, the crate provides the [env_field_wrap](https://docs.rs/serde-env-field/latest/serde_env_field/attr.env_field_wrap.html) attribute that wraps all the fields of a struct or an enum with the `EnvField` type.
The attribute also honors the optional and vector fields.

#### `EnvField` Example

```rust
#[derive(Serialize, Deserialize)]
struct Example {
    name: EnvField<String>,
    size: EnvField<usize>,
    num: EnvField<i32>,
}

std::env::set_var("SIZE", "100");

let de: Example = toml::from_str(r#"
    name = "${NAME:-Default Name}"

    size = "$SIZE"

    num = 42
"#).unwrap();

assert_eq!(&de.name, "Default Name");
assert_eq!(de.size, 100);
assert_eq!(de.num, 42);
```
#### `env_field_wrap` Example

```rust
#[env_field_wrap]
#[derive(Serialize, Deserialize)]
struct Example {
    name: String,
    size: usize,
    num: i32,
}

std::env::set_var("SIZE", "100");

let de: Example = toml::from_str(r#"
    name = "${NAME:-Default Name}"

    size = "$SIZE"

    num = 42
"#).unwrap();

assert_eq!(&de.name, "Default Name");
assert_eq!(de.size, 100);
assert_eq!(de.num, 42);
```

See the documentation of the [EnvField](https://docs.rs/serde-env-field/latest/serde_env_field/struct.EnvField.html) and the [env_field_wrap](https://docs.rs/serde-env-field/latest/serde_env_field/attr.env_field_wrap.html) for details.