https://github.com/rustyyato/cell-project
https://github.com/rustyyato/cell-project
Last synced: 11 months ago
JSON representation
- Host: GitHub
- URL: https://github.com/rustyyato/cell-project
- Owner: RustyYato
- License: mit
- Created: 2020-04-30T21:05:54.000Z (about 6 years ago)
- Default Branch: master
- Last Pushed: 2022-08-08T15:41:15.000Z (almost 4 years ago)
- Last Synced: 2025-07-07T18:24:57.704Z (12 months ago)
- Language: Rust
- Size: 41 KB
- Stars: 8
- Watchers: 1
- Forks: 2
- Open Issues: 2
-
Metadata Files:
- Readme: README.md
- License: LICENSE-MIT
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README
# cell-project
A safe interface to project through shared references to [`core::cell::Cell`](https://!doc.rust-lang.org/core/cell/struct.Cell.html).
Documentation:
https://docs.rs/cell-project
```rust
use std::cell::Cell;
use cell_project::cell_project as cp; // renamed for ergonomics
struct Point {
x: f32,
y: f32,
}
fn get_x_cell(point: &Cell) -> &Cell {
cp!(Point, point.x)
}
```
The syntax for the macro is as follows
```rust compile_fail
let projection = cp!($TypeOfValue, $value_identifier.$field_identifier);
```
You may not pass an expression for `$value_identifier`, if you need to then you should do.
```rust
let value = Cell::new(get_point());
let projection = cp!(Point, value.y);
```
If you need to project through multiple fields then you need to call `cp!` multiple times, once per projection
```rust
struct Pair(T, T);
// let some_pair: &Cell>;
let point = cp!(Pair, some_pair.0);
let x = cp!(Point, point.x);
```
note: for generic types, you can use `_` to infer the generic parameters
```rust
fn get_x_cell(point: &Cell>) -> &Cell {
cp!(Pair<_>, point.0)
}
```
Some limitations, you cannot project an enum variant because that is potentially unsound.
```rust
let x = Cell::new(Some(0));
// let's imagine a macro like `try_cell_project`, which takes a varaint as well as a type
let proj = cell_project::try_cell_project!(Option<_>, Some, x.0).unwrap();
x.set(None); // we can still write to the `Cell` directly
// this will read uninitialized memory (because that's what `None` wrote in)
// and there is no way to fix this. Enums cannot allow safe projection through
// a shared mutable reference (like `&Cell<_>`)
let _ = proj.get();
```
so you cannot project through enums
Another limitation of stable, you can only project to `Sized` types. For example, if I have a type
```rust
struct Unsized(i32, [u8]);
```
Then I can only project to the first field, because the second field is `!Sized`
### features
`nightly` - unlocks `cell_project::nightly_cell_project`, which uses the unstable `#![feature(raw_ref_op)]` to
allow projections to `!Sized` fields.
License: MIT