pub trait Coroutine<R = ()> {
type Yield;
type Return;
// Required method
fn resume(
self: Pin<&mut Self>,
arg: R,
) -> CoroutineState<Self::Yield, Self::Return>;
}coroutine_trait #43122)Expand description
The trait implemented by builtin coroutine types.
Coroutines are currently an experimental language feature in Rust. Added in RFC 2033 coroutines are currently intended to primarily provide a building block for async/await syntax but will likely extend to also providing an ergonomic definition for iterators and other primitives.
The syntax and semantics for coroutines is unstable and will require a further RFC for stabilization. At this time, though, the syntax is closure-like:
#![feature(coroutines)]
#![feature(coroutine_trait)]
#![feature(stmt_expr_attributes)]
use std::ops::{Coroutine, CoroutineState};
use std::pin::Pin;
fn main() {
let mut coroutine = #[coroutine] || {
yield 1;
"foo"
};
match Pin::new(&mut coroutine).resume(()) {
CoroutineState::Yielded(1) => {}
_ => panic!("unexpected return from resume"),
}
match Pin::new(&mut coroutine).resume(()) {
CoroutineState::Complete("foo") => {}
_ => panic!("unexpected return from resume"),
}
}More documentation of coroutines can be found in the unstable book.
Required Associated Types§
sourcetype Yield
🔬This is a nightly-only experimental API. (coroutine_trait #43122)
type Yield
coroutine_trait #43122)The type of value this coroutine yields.
This associated type corresponds to the yield expression and the
values which are allowed to be returned each time a coroutine yields.
For example an iterator-as-a-coroutine would likely have this type as
T, the type being iterated over.
sourcetype Return
🔬This is a nightly-only experimental API. (coroutine_trait #43122)
type Return
coroutine_trait #43122)The type of value this coroutine returns.
This corresponds to the type returned from a coroutine either with a
return statement or implicitly as the last expression of a coroutine
literal. For example futures would use this as Result<T, E> as it
represents a completed future.
Required Methods§
sourcefn resume(
self: Pin<&mut Self>,
arg: R,
) -> CoroutineState<Self::Yield, Self::Return>
🔬This is a nightly-only experimental API. (coroutine_trait #43122)
fn resume( self: Pin<&mut Self>, arg: R, ) -> CoroutineState<Self::Yield, Self::Return>
coroutine_trait #43122)Resumes the execution of this coroutine.
This function will resume execution of the coroutine or start execution
if it hasn’t already. This call will return back into the coroutine’s
last suspension point, resuming execution from the latest yield. The
coroutine will continue executing until it either yields or returns, at
which point this function will return.
§Return value
The CoroutineState enum returned from this function indicates what
state the coroutine is in upon returning. If the Yielded variant is
returned then the coroutine has reached a suspension point and a value
has been yielded out. Coroutines in this state are available for
resumption at a later point.
If Complete is returned then the coroutine has completely finished
with the value provided. It is invalid for the coroutine to be resumed
again.
§Panics
This function may panic if it is called after the Complete variant has
been returned previously. While coroutine literals in the language are
guaranteed to panic on resuming after Complete, this is not guaranteed
for all implementations of the Coroutine trait.