comm-central/third_party/rust/pin-project/README.md

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# pin-project
<!-- tidy:crate-doc:start -->
A crate for safe and ergonomic [pin-projection].
## Usage
Add this to your `Cargo.toml`:
```toml
[dependencies]
pin-project = "1"
```
*Compiler support: requires rustc 1.56+*
## Examples
[`#[pin_project]`][`pin_project`] attribute creates projection types
covering all the fields of struct or enum.
```rust
use std::pin::Pin;
use pin_project::pin_project;
#[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
}
}
```
[*code like this will be generated*][struct-default-expanded]
To use `#[pin_project]` on enums, you need to name the projection type
returned from the method.
```rust
use std::pin::Pin;
use pin_project::pin_project;
#[pin_project(project = EnumProj)]
enum Enum<T, U> {
Pinned(#[pin] T),
Unpinned(U),
}
impl<T, U> Enum<T, U> {
fn method(self: Pin<&mut Self>) {
match self.project() {
EnumProj::Pinned(x) => {
let _: Pin<&mut T> = x;
}
EnumProj::Unpinned(y) => {
let _: &mut U = y;
}
}
}
}
```
[*code like this will be generated*][enum-default-expanded]
See [`#[pin_project]`][`pin_project`] attribute for more details, and
see [examples] directory for more examples and generated code.
## Related Projects
- [pin-project-lite]: A lightweight version of pin-project written with declarative macros.
<!-- tidy:crate-doc:end -->
## License
Licensed under either of [Apache License, Version 2.0](LICENSE-APACHE) or
[MIT license](LICENSE-MIT) 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.