Consider allowing naming the projected type about pin-project HOT 4 CLOSED

At this time I don't have a strong opinion about whether this should be added, but I am a bit concerned that this can complicate the API.

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Given that #[project] isn't really available everywhere, I've come to feel that this makes sense.

Maybe something like this:

#[pin_project(project = FooProj, project_ref = FooProjRef)]
struct Foo<T> {
    #[pin]
    x T: ,
}

impl<T> Foo<'_, T> {}

(It should be mentioned in the documentation that a lifetime is added to the first position in generics.)

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One of the cases that current #[project] cannot support is the following code.

#[pin_project::pin_project(Replace)]
enum E<T, U> {
    A(#[pin] T),
    B(U),
    C,
}

fn foo<T, U>(e: Pin<&mut E<T, Y>>) {
    if let E::A(_a) = e.project() { // needs #[project]
        // ..
    } else if E::B(_b) = e.project_replace(E::C) { // needs #[project_replace]
        //
    }
}

from pin-project.

It should be mentioned in the documentation that a lifetime is added to the first position in generics.

Oh, it seems I forgot to do this in #202.

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