serde-hashkey 0.3.0

Space efficient, in-memory key based on serde.
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# serde-hashkey

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Serde-based in-memory key serialization.

This allows any serde-serializable type to be converted into a value which
implements `PartialEq`, `Eq`, `ParialOrd`, `Ord`, and `Hash`.

[Key] is useful because it allows for a form of type-erasure. Let's say you
want to build a generic in-memory key-value store where you want to store
arbitrary serde-serializable keys. This is typical for things like caches or
dependency injection frameworks.

### Float policies

By default, [Key] can't include floating point types such as `f32` and
`f64`. Neither of these are [totally ordered nor hashable].

To enable the [Key] type to use `f32` and `f64` it can be constructed with a
specific float policy.

Available float policies are:
* [RejectFloat] - the default behavior when using [to_key].
* [OrderedFloat] - the behavior when using [to_key_with_ordered_float]. The
  `ordered-float` feature must be enabled to use this. The behavior is
  derived from the [`ordered-float` crate].

### Features

* `ordered-float` - Enables serializing floating point numbers through
  behavior derived from the [`ordered-float` crate]

### Examples

> You can run this example with `cargo run --example book`

```rust
use serde_derive::{Deserialize, Serialize};
use serde_hashkey::{from_key, to_key, Error, Key};
use std::{collections::HashMap, error};

#[derive(Debug, PartialEq, Eq, Serialize, Deserialize)]
struct Author {
    name: String,
    age: u32,
}

#[derive(Debug, PartialEq, Eq, Serialize, Deserialize)]
struct Book {
    title: String,
    author: Author,
}

fn main() -> Result<(), Box<dyn error::Error>> {
    let book = Book {
        title: String::from("Birds of a feather"),
        author: Author {
            name: String::from("Noah"),
            age: 42,
        },
    };

    let key = to_key(&book)?;

    let mut ratings = HashMap::new();
    ratings.insert(key.clone(), 5);

    println!("ratings: {:?}", ratings);

    println!(
        "book as json (through key): {}",
        serde_json::to_string_pretty(&key)?
    );

    println!(
        "book as json (through original object): {}",
        serde_json::to_string_pretty(&book)?
    );

    Ok(())
}
```

[totally ordered nor hashable]: https://internals.rust-lang.org/t/f32-f64-should-implement-hash/5436
[Key]: https://docs.rs/serde-hashkey/0/serde_hashkey/enum.Key.html
[to_key]: https://docs.rs/serde-hashkey/0/serde_hashkey/fn.to_key.html
[RejectFloat]: https://docs.rs/serde-hashkey/0/serde_hashkey/enum.RejectFloat.html
[OrderedFloat]: https://docs.rs/serde-hashkey/0/serde_hashkey/enum.OrderedFloat.html
[to_key_with_ordered_float]: https://docs.rs/serde-hashkey/0/serde_hashkey/fn.to_key_with_ordered_float.html
[`ordered-float` crate]: https://docs.rs/ordered-float/2/ordered_float/

License: MIT/Apache-2.0