pin-project-lite

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

Usage

Add this to your Cargo.toml:

toml [dependencies] pin-project-lite = "0.2"

Compiler support: requires rustc 1.37+

Examples

[pin_project!] macro creates a projection type covering all the fields of struct.

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

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

impl Struct { fn method(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 } } ```

To use [pin_project!] on enums, you need to name the projection type returned from the method.

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

pin_project! { #[project = EnumProj] enum Enum { Variant { #[pin] pinned: T, unpinned: U }, } }

impl Enum { fn method(self: Pin<&mut Self>) { match self.project() { EnumProj::Variant { pinned, unpinned } => { let _: Pin<&mut T> = pinned; let _: &mut U = unpinned; } } } } ```

[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: No support for custom Drop implementation

pin-project supports this by #[pinned_drop].

Different: No support for custom Unpin implementation

pin-project supports this by UnsafeUnpin and !Unpin.

Different: No support for tuple structs and tuple variants

pin-project supports this.

License

Licensed under either of Apache License, Version 2.0 or MIT license at your option.

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.