Ecosyste.ms: Awesome

An open API service indexing awesome lists of open source software.

Awesome Lists | Featured Topics | Projects

https://github.com/xfbs/imstr

Immutable strings, in Rust.
https://github.com/xfbs/imstr

cheap clone copy-on-write cow immutable rust slice string zero-copy

Last synced: about 2 months ago
JSON representation

Immutable strings, in Rust.

Awesome Lists containing this project

README 

        
# Immutable Strings



[![crates.io](https://img.shields.io/crates/v/imstr.svg)](https://crates.io/crates/imstr)

[![docs.rs](https://img.shields.io/docsrs/imstr)](https://docs.rs/imstr)



This crate offers a cheaply cloneable and sliceable UTF-8 string type. It is

inspired by the [`bytes`] crate, which offers zero-copy byte slices, and the

[`im`] crate which offers immutable copy-on-write data structures. It offers

a standard-library `String`-compatible API.



Internally, the crate uses a standard library string stored in a smart pointer,

and a range into that `String`.  This allows for cheap zero-copy cloning and

slicing of the string. This is especially useful for parsing operations, where

a large string needs to be sliced into a lot of substrings. 



> TL;DR: This crate offers an `ImString`

> type that acts as a `String` (in that it can be modified and used in the same

> way), an `Arc` (in that it is cheap to clone) and an `&str` (in that

> it is cheap to slice) all in one, owned type.



![Diagram of ImString Internals](diagram.png)



This crate offers a safe API that ensures that every string and every string

slice is UTF-8 encoded. It does not allow slicing of strings within UTF-8

multibyte sequences. It offers `try_*` functions for every operation that can

fail to avoid panics. It also uses extensive unit testing with a full test

coverage to ensure that there is no unsoundness.



## Features



**Efficient Cloning**: The crate's architecture enables low-cost (zero-copy)

clone and slice creation, making it ideal for parsing strings that are widely

shared.



**Efficient Slicing**: The crate's architecture enables low-cost (zero-copy)

slice creation, making it ideal for parsing operations where one large input

string is slices into many smaller strings.



**Copy on Write**: Despite being cheap to clone and slice, it allows for

mutation using copy-on-write. For strings that are not shared, it has an

optimisation to be able to mutate it in-place safely to avoid unnecessary

copying.



**Compatibility**: The API is designed to closely resemble Rust's standard

library [`String`], facilitating smooth integration and being almost a drop-in

replacement. It also integrates with many popular Rust crates, such as

[`serde`], [`peg`] and [`nom`].



**Generic over Storage**: The crate is flexible in terms of how the data is

stored.  It allows for using `Arc` for multithreaded applications and

`Rc` for single-threaded use, providing adaptability to different

storage requirements and avoiding the need to pay for atomic operations when

they are not needed.



**Safety**: The crate enforces that all strings and string slices are UTF-8

encoded. Any methods that might violate this are marked as unsafe. All methods

that can fail have a `try_*` variant that will not panic. Use of safe functions

cannot result in unsound behaviour.



## Example



```rust

use imstr::ImString;



// Create new ImString, allocates data.

let mut string = ImString::from("Hello, World");



// Edit: happens in-place (because this is the only reference).

string.push_str("!");



// Clone: this is zero-copy.

let clone = string.clone();



// Slice: this is zero-copy.

let hello = string.slice(0..5);

assert_eq!(hello, "Hello");



// Slice: this is zero-copy.

let world = string.slice(7..12);

assert_eq!(world, "World");



// Here we have to copy only the part that the slice refers to so it can be modified.

let hello = hello + "!";

assert_eq!(hello, "Hello!");

```



## Optional Features



Optional features that can be turned on using feature-flags.



| Feature | Description |

| --- | --- |

| `serde` | Serialize and deserialize `ImString` fields as strings with the [`serde`] crate. |

| `peg` | Use `ImString` as the data structure that is parsed with the [`peg`] crate. See [`peg-list.rs`](examples/peg-list.rs) for an example. |

| `nom` | Allow `ImString` to be used to build parsers with [`nom`]. See [`nom-json.rs`](examples/nom-json.rs) for an example. |



## Similar



> There are several crates similar to this, which are listed in the [Rust String

> Benchmarks](https://github.com/rosetta-rs/string-rosetta-rs). You may want

> to check the other crates out as well.



This is a comparison of this crate to other, similar crates. The comparison is

made on these features:



- **Cheap Clone**: is it a zero-copy operation to clone a string?

- **Cheap Slice** 🍕: is it possibly to cheaply slice a string?

- **Mutable**: is it possible to modify strings?

- **Generic Storage**: is it possible to swap out the storage mechanism?

- **String Compatible**: is it compatible with [`String`]?



Here is the data, with links to the crates for further examination:



| Crate | Cheap Clone| Cheap Slice | Mutable | Generic Storage | String Compatible | Notes |

| --- | --- | --- | --- | --- | --- | --- |

| [`imstr`] | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark: | :heavy_check_mark: | This crate. |

| [`tendril`] |:heavy_check_mark:|:heavy_check_mark:|:heavy_check_mark:|:heavy_check_mark:|❌| Complex implementation. API not quite compatible with [`String`], but otherwise closest to what this crate does. |

| [`immut_string`] |:heavy_check_mark:|❌| 🟡 (no optimization) |❌|❌| Simply a wrapper around `Arc`. |

| [`immutable_string`] |:heavy_check_mark:|❌|❌|❌|❌| Wrapper around `Arc`. |

| [`arccstr`] |:heavy_check_mark:|❌|❌|❌|❌| Not UTF-8 (Null-terminated C string). Hand-written `Arc` implementation. |

| [`implicit-clone`] |:heavy_check_mark:|❌|❌|🟡|:heavy_check_mark:| Immutable string library. Has `sync` and `unsync` variants. |

| [`semistr`] |❌|❌|❌|❌|❌| Stores short strings inline. |

| [`quetta`] |:heavy_check_mark:|:heavy_check_mark:|❌|❌|❌| Wrapper around `Arc` that can be sliced. |

| [`bytesstr`] |:heavy_check_mark:|🟡|❌|❌|❌| Wrapper around `Bytes`. Cannot be directly sliced. |

| [`fast-str`] |:heavy_check_mark:|❌|❌|❌|❌| Looks like there could be some unsafety. |

| [`flexstr`] |:heavy_check_mark:|❌|❌|:heavy_check_mark:|❌| |

| [`bytestring`] |:heavy_check_mark:|🟡|❌|❌|❌| Wrapper around `Bytes`. Used by `actix`. Can be indirectly sliced using `slice_ref()`. |

| [`arcstr`] |:heavy_check_mark:|:heavy_check_mark:|❌|❌|❌| Can store string literal as `&'static str`. |

| [`cowstr`] |:heavy_check_mark:|❌|:heavy_check_mark:|❌|❌| Reimplements `Arc`, custom allocation strategy. |

| [`strck`] |❌|❌|❌|:heavy_check_mark:|❌| Typechecked string library. |



## License



MIT, see [LICENSE.md](LICENSE.md).



[`imstr`]: https://crates.io/crates/imstr

[`tendril`]: https://crates.io/crates/tendril

[`immut_string`]: https://crates.io/crates/immut_string

[`immutable_string`]: https://crates.io/crates/immutable_string

[`arccstr`]: https://crates.io/crates/arccstr

[`implicit-clone`]: https://crates.io/crates/implicit-clone

[`semistr`]: https://crates.io/crates/semistr

[`quetta`]: https://crates.io/crates/quetta

[`bytesstr`]: https://crates.io/crates/bytesstr

[`fast-str`]: https://crates.io/crates/fast-str

[`flexstr`]: https://crates.io/crates/flexstr

[`bytestring`]: https://crates.io/crates/bytestring

[`arcstr`]: https://crates.io/crates/arcstr

[`cowstr`]: https://crates.io/crates/cowstr

[`strck`]: https://crates.io/crates/strck

[`String`]: https://doc.rust-lang.org/std/string/struct.String.html

[`bytes`]: https://crates.io/crates/bytes

[`im`]: https://crates.io/crates/im

[`serde`]: https://crates.io/crates/serde

[`peg`]: https://crates.io/crates/peg

[`nom`]: https://crates.io/crates/nom