Simplify GenFuture API.

Author: Without Boats

src/libcore/raw.rs

@@ -104,21 +104,7 @@ pub struct TraitObject {
 /// depend on it.
 #[allow(missing_debug_implementations, dead_code)]
 #[unstable(feature = "gen_future", issue = "50547")]
-pub struct GenFuture<G, R> {
-    gen: G,
-    marker: ::marker::PhantomData<R>,
-}
-
-/// Construct a future from a generator (used in lowering async functions).
-///
-/// This is a permanently unstable API used by the compiler. You should not
-/// depend on it.
-#[unstable(feature = "gen_future", issue = "50547")]
-pub fn gen_future<G>(gen: G) -> GenFuture<G, G::Return> where
-    G: ::ops::Generator<Yield = ()>
-{
-    GenFuture { gen, marker: ::marker::PhantomData }
-}
+pub struct GenFuture<G: ::ops::Generator<Yield = (), Return = R>, R>(pub G);
 
 #[unstable(feature = "gen_future", issue = "50547")]
 impl<G> ::future::Future for GenFuture<G, G::Return> where