Manually type the outputs of a generator using `gen!`

[philip-peterson]

Hi there,

I am wanting to have a generator that will yield values that are an Rc<dyn T>. Currently I have to do it like so:

async fn produce_pages(mut co: Co<'_, Rc<dyn GeneratedPage>>) {
    co.yield_(Rc::new(HomePage {})).await;
    co.yield_(Rc::new(ContactPage {})).await;
}

fn foo() -> () {
    let_gen_using!(gen_all_pages, produce);
    gen_all_pages.into_iter().collect();
}

This means that foo cannot return the iterator sadly because of the use of let_gen_using, which leaks the shelf value which is owned by the foo function.

The whole reason I need to use the producer pattern is because gen!() doesn't accept a type argument (which is needed because of the dyn); would it be possible to have it allow a field that specifies what type the Rust compiler should know the generator results to be?