[−][src]Crate pin_project_lite

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

Examples

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

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 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
    }
}

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.

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 by #[pinned_drop].

Different: No support for custom Unpin implementation

pin-project supports this by UnsafeUnpin and !Unpin.

Different: No support for pattern matching and destructing

pin-project supports this.

Macros

pin_project

A macro that creates a projection type covering all the fields of struct.