| use crate::marker::Unpin; |
| use crate::pin::Pin; |
| |
| /// The result of a generator resumption. |
| /// |
| /// This enum is returned from the `Generator::resume` method and indicates the |
| /// possible return values of a generator. Currently this corresponds to either |
| /// a suspension point (`Yielded`) or a termination point (`Complete`). |
| #[derive(Clone, Copy, PartialEq, PartialOrd, Eq, Ord, Debug, Hash)] |
| #[lang = "generator_state"] |
| #[unstable(feature = "generator_trait", issue = "43122")] |
| pub enum GeneratorState<Y, R> { |
| /// The generator suspended with a value. |
| /// |
| /// This state indicates that a generator has been suspended, and typically |
| /// corresponds to a `yield` statement. The value provided in this variant |
| /// corresponds to the expression passed to `yield` and allows generators to |
| /// provide a value each time they yield. |
| Yielded(Y), |
| |
| /// The generator completed with a return value. |
| /// |
| /// This state indicates that a generator has finished execution with the |
| /// provided value. Once a generator has returned `Complete` it is |
| /// considered a programmer error to call `resume` again. |
| Complete(R), |
| } |
| |
| /// The trait implemented by builtin generator types. |
| /// |
| /// Generators, also commonly referred to as coroutines, are currently an |
| /// experimental language feature in Rust. Added in [RFC 2033] generators 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 generators is unstable and will require a |
| /// further RFC for stabilization. At this time, though, the syntax is |
| /// closure-like: |
| /// |
| /// ```rust |
| /// #![feature(generators, generator_trait)] |
| /// |
| /// use std::ops::{Generator, GeneratorState}; |
| /// use std::pin::Pin; |
| /// |
| /// fn main() { |
| /// let mut generator = || { |
| /// yield 1; |
| /// return "foo" |
| /// }; |
| /// |
| /// match Pin::new(&mut generator).resume() { |
| /// GeneratorState::Yielded(1) => {} |
| /// _ => panic!("unexpected return from resume"), |
| /// } |
| /// match Pin::new(&mut generator).resume() { |
| /// GeneratorState::Complete("foo") => {} |
| /// _ => panic!("unexpected return from resume"), |
| /// } |
| /// } |
| /// ``` |
| /// |
| /// More documentation of generators can be found in the unstable book. |
| /// |
| /// [RFC 2033]: https://github.com/rust-lang/rfcs/pull/2033 |
| #[lang = "generator"] |
| #[unstable(feature = "generator_trait", issue = "43122")] |
| #[fundamental] |
| pub trait Generator { |
| /// The type of value this generator yields. |
| /// |
| /// This associated type corresponds to the `yield` expression and the |
| /// values which are allowed to be returned each time a generator yields. |
| /// For example an iterator-as-a-generator would likely have this type as |
| /// `T`, the type being iterated over. |
| type Yield; |
| |
| /// The type of value this generator returns. |
| /// |
| /// This corresponds to the type returned from a generator either with a |
| /// `return` statement or implicitly as the last expression of a generator |
| /// literal. For example futures would use this as `Result<T, E>` as it |
| /// represents a completed future. |
| type Return; |
| |
| /// Resumes the execution of this generator. |
| /// |
| /// This function will resume execution of the generator or start execution |
| /// if it hasn't already. This call will return back into the generator's |
| /// last suspension point, resuming execution from the latest `yield`. The |
| /// generator will continue executing until it either yields or returns, at |
| /// which point this function will return. |
| /// |
| /// # Return value |
| /// |
| /// The `GeneratorState` enum returned from this function indicates what |
| /// state the generator is in upon returning. If the `Yielded` variant is |
| /// returned then the generator has reached a suspension point and a value |
| /// has been yielded out. Generators in this state are available for |
| /// resumption at a later point. |
| /// |
| /// If `Complete` is returned then the generator has completely finished |
| /// with the value provided. It is invalid for the generator to be resumed |
| /// again. |
| /// |
| /// # Panics |
| /// |
| /// This function may panic if it is called after the `Complete` variant has |
| /// been returned previously. While generator literals in the language are |
| /// guaranteed to panic on resuming after `Complete`, this is not guaranteed |
| /// for all implementations of the `Generator` trait. |
| fn resume(self: Pin<&mut Self>) -> GeneratorState<Self::Yield, Self::Return>; |
| } |
| |
| #[unstable(feature = "generator_trait", issue = "43122")] |
| impl<G: ?Sized + Generator> Generator for Pin<&mut G> { |
| type Yield = G::Yield; |
| type Return = G::Return; |
| |
| fn resume(mut self: Pin<&mut Self>) -> GeneratorState<Self::Yield, Self::Return> { |
| G::resume((*self).as_mut()) |
| } |
| } |
| |
| #[unstable(feature = "generator_trait", issue = "43122")] |
| impl<G: ?Sized + Generator + Unpin> Generator for &mut G { |
| type Yield = G::Yield; |
| type Return = G::Return; |
| |
| fn resume(mut self: Pin<&mut Self>) -> GeneratorState<Self::Yield, Self::Return> { |
| G::resume(Pin::new(&mut *self)) |
| } |
| } |