# pin-project-lite

[![crates-badge]][crates-url]
[![docs-badge]][docs-url]
[![license-badge]][license]
[![rustc-badge]][rustc-url]

[crates-badge]: https://img.shields.io/crates/v/pin-project-lite.svg
[crates-url]: https://crates.io/crates/pin-project-lite
[docs-badge]: https://docs.rs/pin-project-lite/badge.svg
[docs-url]: https://docs.rs/pin-project-lite
[license-badge]: https://img.shields.io/crates/l/pin-project-lite.svg
[license]: #license
[rustc-badge]: https://img.shields.io/badge/rustc-1.37+-lightgray.svg
[rustc-url]: https://blog.rust-lang.org/2019/08/15/Rust-1.37.0.html

A lightweight version of [pin-project] written with declarative macros.

## Usage

Add this to your `Cargo.toml`:

```toml
[dependencies]
pin-project-lite = "0.1"
```

The current pin-project-lite requires Rust 1.37 or later.

## Examples

```rust
use pin_project_lite::pin_project;
use std::pin::Pin;

pin_project! {
    struct Struct<T, U> {
        #[pin]
        pinned: T,
        unpinned: U,
    }
}

impl<T, U> Struct<T, U> {
    fn foo(self: Pin<&mut Self>) {
        let this = self.project();
        let _: Pin<&mut T> = this.pinned; // Pinned reference to the field
        let _: &mut U = this.unpinned; // Normal reference to the field
    }
}
```

## [pin-project] vs pin-project-lite

Here are some similarities and differences compared to [pin-project].

### Similar: Safety

pin-project-lite guarantees safety in much the same way as [pin-project]. Both are completely safe unless you write other unsafe code.

### Different: Minimal design

This library does not tackle as expansive of a range of use cases as [pin-project] does. If your use case is not already covered, please use [pin-project].

### Different: No proc-macro related dependencies

This is the **only** reason to use this crate. However, **if you already have proc-macro related dependencies in your crate's dependency graph, there is no benefit from using this crate.** (Note: There is almost no difference in the amount of code generated between [pin-project] and pin-project-lite.)

### Different: No useful error messages

This macro does not handle any invalid input. So error messages are not to be useful in most cases. If you do need useful error messages, then upon error you can pass the same input to [pin-project] to receive a helpful description of the compile error.

### Different: Structs only

pin-project-lite will refuse anything other than a braced struct with named fields. Enums and tuple structs are not supported.

### Different: No support for custom Drop implementation

[pin-project supports this.][pinned-drop]

### Different: No support for custom Unpin implementation

[pin-project supports this.][unsafe-unpin]

### Different: No support for pattern matching and destructing

[pin-project supports this.][projection-helper]

[pin-project]: https://github.com/taiki-e/pin-project
[pinned-drop]: https://docs.rs/pin-project/0.4/pin_project/attr.pin_project.html#pinned_drop
[unsafe-unpin]: https://docs.rs/pin-project/0.4/pin_project/trait.UnsafeUnpin.html
[projection-helper]: https://docs.rs/pin-project/0.4/pin_project/attr.project.html#let-bindings

## License

Licensed under either of

* Apache License, Version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or <http://www.apache.org/licenses/LICENSE-2.0>)
* MIT license ([LICENSE-MIT](LICENSE-MIT) or <http://opensource.org/licenses/MIT>)

at your option.

### Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.