# musli-descriptive
[
](https://github.com/udoprog/musli)
[
](https://crates.io/crates/musli-descriptive)
[
](https://docs.rs/musli-descriptive)
[
](https://github.com/udoprog/musli/actions?query=branch%3Amain)
A fully self-descriptive format for [Müsli].
Descriptive encoding is fully upgrade stable:
* ✔ Can tolerate missing fields if they are annotated with
`#[musli(default)]`.
* ✔ Can skip over unknown fields.
* ✔ Can be fully converted back and forth between dynamic containers such as
the [Value] type.
* ✔ Can handle coercion from different types of primitive types, such as
signed to unsigned integers. So primitive field types can be assuming they
only inhabit compatible values.
This means that it's suitable as a wire and general interchange format. It's
also suitable for dynamically translating to and from different wire formats
such as JSON without having access to the data model.
```rust
use musli::{Encode, Decode};
#[derive(Debug, PartialEq, Encode, Decode)]
struct Version1 {
name: String,
}
#[derive(Debug, PartialEq, Encode, Decode)]
struct Version2 {
name: String,
#[musli(default)]
age: Option,
}
let version2 = musli_descriptive::to_vec(&Version2 {
name: String::from("Aristotle"),
age: Some(62),
})?;
let version1: Version1 = musli_descriptive::decode(version2.as_slice())?;
assert_eq!(version1, Version1 {
name: String::from("Aristotle"),
});
```
## Configuring
To configure the behavior of the wire format you can use the [`Encoding`]
type:
```rust
use musli_descriptive::Encoding;
use musli::{Encode, Decode};
const CONFIG: Encoding = Encoding::new();
#[derive(Debug, PartialEq, Encode, Decode)]
struct Struct<'a> {
name: &'a str,
age: u32,
}
let mut out = Vec::new();
let expected = Struct {
name: "Aristotle",
age: 61,
};
CONFIG.encode(&mut out, &expected)?;
let actual = CONFIG.decode(&out[..])?;
assert_eq!(expected, actual);
```
## Implementation details
Each field is prefix *typed* with a single byte tag that describes exactly
the type which is contained in the field.
[default encoding format]: https://docs.rs/musli-wire/latest/musli-wire/struct.Encoding.html
[MAX_INLINE_LEN]: https://docs.rs/musli-wire/latest/musli_descriptive/tag/constant.MAX_INLINE_LEN.html
[Müsli]: https://docs.rs/musli
[`Encoding`]: https://docs.rs/musli-wire/latest/musli-wire/struct.Encoding.html
[Value]: https://docs.rs/musli-value