Crate escher[−][src]
Self-referencial structs using async stacks
Escher is an extremely simple library providing a safe and sound API to build self-referencial structs. It works by (ab)using the async await trasformation of rustc. If you’d like to know more about the inner workings please take a look at the How it works section and the source code.
Compared to the state of the art escher:
- Is only around 100 lines of well-commented code
- Contains only two
unsafe
calls that are well argued for - Uses rustc for all the analysis. If it compiles, the self references are correct
Usage
This library provides the Escher
You construct a self reference by calling Escher’s constructor and providing an async closure
that will initialize your self-references on its stack. Your closure will be provided with a
capturer r
that has a single capture() method that consumes r
.
Note: It is important to
.await
the result.capture()
in order for escher to correctly initialize your struct.
Once all the data and references are created you can capture the desired ones. Simple references to owned data can be captured directly (see first example).
To capture more than one variable or capture references to non-owned data you will have to define your own reference struct that derives Rebindable (see second example).
Examples
Simple &str
view into an owned Vec<u8>
The simplest way to use Escher is to create a reference of some data and then capture it:
use escher::Escher; let escher_heart = Escher::new(|r| async move { let data: Vec<u8> = vec![240, 159, 146, 150]; let sparkle_heart = std::str::from_utf8(&data).unwrap(); r.capture(sparkle_heart).await; }); assert_eq!("💖", *escher_heart.as_ref());
Capturing both a Vec<u8>
and a &str
view into it
In order to capture more than one things you can define a struct that will be used to capture the variables:
use escher::{Escher, Rebindable}; #[derive(Rebindable)] struct VecStr<'this> { data: &'this Vec<u8>, s: &'this str, } let escher_heart = Escher::new(|r| async move { let data: Vec<u8> = vec![240, 159, 146, 150]; r.capture(VecStr{ data: &data, s: std::str::from_utf8(&data).unwrap(), }).await; }); assert_eq!(240, escher_heart.as_ref().data[0]); assert_eq!("💖", escher_heart.as_ref().s);
Capturing a mutable &mut str
view into a Vec<u8>
If you capture a mutable reference to some piece of data then you cannot capture the data itself like the previous example. This is mandatory as doing otherwise would create two mutable references into the same piece of data which is not allowed.
use escher::Escher; let mut name = Escher::new(|r| async move { let mut data: Vec<u8> = vec![101, 115, 99, 104, 101, 114]; let name = std::str::from_utf8_mut(&mut data).unwrap(); r.capture(name).await; }); assert_eq!("escher", *name.as_ref()); name.as_mut().make_ascii_uppercase(); assert_eq!("ESCHER", *name.as_ref());
Capturing multiple mixed references
use escher::{Escher, Rebindable}; #[derive(Rebindable)] struct MyStruct<'this> { int_data: &'this Box<i32>, int_ref: &'this i32, float_ref: &'this mut f32, } let mut my_value = Escher::new(|r| async move { let int_data = Box::new(42); let mut float_data = Box::new(3.14); r.capture(MyStruct{ int_data: &int_data, int_ref: &int_data, float_ref: &mut float_data, }).await; }); assert_eq!(Box::new(42), *my_value.as_ref().int_data); assert_eq!(3.14, *my_value.as_ref().float_ref); *my_value.as_mut().float_ref = (*my_value.as_ref().int_ref as f32) * 2.0; assert_eq!(84.0, *my_value.as_ref().float_ref);
Structs
Capturer | An instance of |
Escher | A containter of a self referencial struct. The self-referencial struct is constructed with the aid of the async/await machinery of rustc, see Escher::new. |
Traits
RebindTo | The |
Rebindable | Marker trait for any type that implements RebindTo for any lifetime. All types can derive this trait using the Rebindable derive macro. |
Type Definitions
Rebind | Type-level function that takes a lifetime |
Derive Macros
Rebindable | This trait can be derived for any struct, enum, or union to make its lifetimes rebindable and thus compatible with the Rebind type level function. |