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https://github.com/orium/archery

Abstract over the atomicity of reference-counting pointers in rust
https://github.com/orium/archery

arc concurrency memory-management rc reference-counting rust

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Abstract over the atomicity of reference-counting pointers in rust

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# `archery`



`archery` is a rust library that offers a way to abstraction over

[`Rc`](https://doc.rust-lang.org/stable/alloc/rc/struct.Rc.html) and

[`Arc`](https://doc.rust-lang.org/stable/alloc/sync/struct.Arc.html) smart pointers.

This allows you to create data structures where the pointer type is parameterizable, so you can

[avoid the overhead of `Arc`](https://doc.rust-lang.org/stable/alloc/sync/struct.Arc.html#thread-safety)

when you don’t need to share data across threads.



In languages that supports

[higher-kinded polymorphism](https://en.wikipedia.org/wiki/Type_class#Higher-kinded_polymorphism)

this would be simple to achieve without any library, but

[rust does not support that yet](https://github.com/rust-lang/rfcs/issues/324).

To mimic higher-kinded polymorphism `archery` implements the approach suggested by

Joshua Liebow-Feeser in

“[Rust has higher kinded types already… sort of](https://joshlf.com/post/2018/10/18/rust-higher-kinded-types-already/)”.

While [other approaches](#alternative-approaches) exist, they seem to always offer poor

ergonomics for the user.



## Setup



To use `archery` add the following to your `Cargo.toml`:



```toml

[dependencies]

archery = ""

```



## Using `archery`



`archery` defines a [`SharedPointer`](https://docs.rs/archery/latest/archery/shared_pointer/struct.SharedPointer.html)

that receives the [kind of pointer](https://docs.rs/archery/latest/archery/shared_pointer/kind/trait.SharedPointerKind.html)

as a type parameter.  This gives you a convenient and ergonomic way to abstract the pointer

type away.



### Example



Declare a data structure with the pointer kind as a type parameter bounded by

[`SharedPointerKind`](https://docs.rs/archery/latest/archery/shared_pointer/kind/trait.SharedPointerKind.html):



```rust

use archery::*;



struct KeyValuePair {

    pub key: SharedPointer,

    pub value: SharedPointer,

}



impl KeyValuePair {

    fn new(key: K, value: V) -> KeyValuePair {

        KeyValuePair {

            key: SharedPointer::new(key),

            value: SharedPointer::new(value),

        }

    }

}

```



To use it just plug-in the kind of pointer you want:



```rust

let pair: KeyValuePair<_, _, RcK> =

    KeyValuePair::new("António Variações", 1944);



assert_eq!(*pair.value, 1944);

```



### `triomphe::Arc`



You can also use [`triomphe::Arc`](https://docs.rs/triomphe/latest/triomphe/struct.Arc.html)

as the backing implementation of a [`SharedPointer`](https://docs.rs/archery/latest/archery/shared_pointer/struct.SharedPointer.html).

This is generally faster than [`std::sync::Arc`](https://doc.rust-lang.org/stable/alloc/sync/struct.Arc.html).

Read [`triomphe`’s crate documentation](https://docs.rs/triomphe/latest/triomphe/) to learn more

about it.



To use it you need to enable the `triomphe` feature in `archery`. Use `ArcTK` as the pointer

kind in [`SharedPointer`](https://docs.rs/archery/latest/archery/shared_pointer/struct.SharedPointer.html).



### Serialization



We support serialization through [serde](https://crates.io/crates/serde).  To use it

enable the `serde` feature.  To do so change the archery dependency in your `Cargo.toml` to



```toml

[dependencies]

archery = { version = "", features = ["serde"] }

```

## Limitations



Currently it is not possible to have unsized types inside a

[`SharedPointer`](https://docs.rs/archery/latest/archery/shared_pointer/struct.SharedPointer.html).  As a workaround you can put the

unsized type inside a [`Box`](https://doc.rust-lang.org/stable/alloc/boxed/struct.Box.html).



## Alternative approaches



An alternative to the approach taken by `archery` is to use traits with associated types to encode

type-level functions.  This has been suggested

[multiple](https://github.com/orium/rpds/issues/7#issuecomment-362635901)

[times](https://joshlf.com/post/2018/10/18/rust-higher-kinded-types-already/#comment-4160863400),

but offers ugly ergonomics (see

[here](https://github.com/Marwes/rpds/blob/e482d5abbaa6c876d7c624e497affe7299bbeece/src/sequence/vector/mod.rs#L153)

and [here](https://github.com/Marwes/rpds/blob/e482d5abbaa6c876d7c624e497affe7299bbeece/src/sequence/vector/mod.rs#L249)).