https://github.com/QuarticCat/enum-ptr

Ergonomic tagged pointer
https://github.com/QuarticCat/enum-ptr

rust

Last synced: 3 months ago
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Ergonomic tagged pointer

• Host: GitHub
• URL: https://github.com/QuarticCat/enum-ptr
• Owner: QuarticCat
• License: apache-2.0
• Created: 2022-10-29T09:57:26.000Z (over 2 years ago)
• Default Branch: main
• Last Pushed: 2023-08-25T02:37:21.000Z (over 1 year ago)
• Last Synced: 2024-05-29T10:12:51.043Z (8 months ago)
• Topics: rust
• Language: Rust
• Homepage: https://crates.io/crates/enum-ptr
• Size: 155 KB
• Stars: 28
• Watchers: 3
• Forks: 0
• Open Issues: 2
• Metadata Files:
  • Readme: README.md
  • License: LICENSE-APACHE

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README

        
# Enum Ptr

[![crates.io](https://img.shields.io/crates/v/enum-ptr)](https://crates.io/crates/enum-ptr)

[![docs.rs](https://img.shields.io/badge/docs.rs-enum--ptr-latest)](https://docs.rs/enum-ptr)

This crate provides a custom derive macro `EnumPtr` to generate bridges between an enum `T` and `Compact` with minimum cost. `Compact` is the compact representation of `T`, and it is only one pointer wide.

In other words, this crate is a library for defining tagged pointers in ergonomic way, even supporting different pointer types (`&`, `Box`, `Arc`, etc) as different `enum` variants.

For example, the following code

```rust

use enum_ptr::EnumPtr;

#[derive(EnumPtr)]

#[repr(C, usize)]

enum Foo<'a> {

    A(&'a i32),

    B(Box),

}

```

will generate

```rust

impl<'a> From> for Compact> {

    // ...

}

impl<'a> From>> for Foo<'a> {

    // ...

}

```

Since `&i32` and `Box` are aligned by 4 bytes, the lowest 2 bits of them are always zeros. `Compact>` utilizes these bits to store the tag (discriminant).

## Features

- No need to write unsafe pointer operations

- Supports various types and can be extended

- Supports `no_std`

- Minimum type conversion cost

- Passes `cargo +nightly miri test` with strict provenance enabled.

## Testing

```console

$ cargo test

$ cargo +nightly miri test

```

## Credits

- Thanks to [@oxalica](https://github.com/oxalica) for reviewing this crate and providing a lot of helpful suggestions.

## License

This project is licensed under either of

- Apache License, Version 2.0, ([LICENSE-APACHE](/LICENSE-APACHE) or [http://www.apache.org/licenses/LICENSE-2.0](http://www.apache.org/licenses/LICENSE-2.0))

- MIT license ([LICENSE-MIT](/LICENSE-MIT) or [http://opensource.org/licenses/MIT](http://opensource.org/licenses/MIT))

at your option.