main.rs

#![feature(generator_trait)]
#![feature(generators)]

use std::ops::{Generator, GeneratorState};
use std::pin::Pin;

use futures::pin_mut;

struct GeneratorIteratorImpl<T>(T);

trait GeneratorIterator
where
    Self: Generator<(), Return = ()> + Sized,
{
    fn iter(self) -> GeneratorIteratorImpl<Self>
    where
        Self: Unpin;

    fn iter_boxed(self) -> GeneratorIteratorImpl<Pin<Box<Self>>>;
}

impl<T> GeneratorIterator for T
where
    Self: Generator<(), Return = ()> + Sized,
{
    fn iter(self) -> GeneratorIteratorImpl<Self>
    where
        Self: Unpin,
    {
        GeneratorIteratorImpl(self)
    }

    fn iter_boxed(self) -> GeneratorIteratorImpl<Pin<Box<Self>>> {
        GeneratorIteratorImpl(Box::pin(self))
    }
}

impl<T> Iterator for GeneratorIteratorImpl<T>
where
    T: Generator<(), Return = ()> + Unpin,
{
    type Item = T::Yield;

    fn next(&mut self) -> Option<Self::Item> {
        match Pin::new(&mut self.0).resume(()) {
            GeneratorState::Yielded(a) => Some(a),
            GeneratorState::Complete(()) => None,
        }
    }
}

fn main() {
    let gen = static || {
        yield 1;
        yield 2;
        yield 3;
    };

    pin_mut!(gen);

    for n in gen.iter() {
        println!("{n}");
    }
}