Add future::poll_fn implementation

Author: kpp

README.md

@@ -25,7 +25,7 @@ Future
 - [x] future::map_err
 - [x] future::map_ok
 - [x] future::or_else
-- [ ] future::poll_fn
+- [x] future::poll_fn
 - [x] future::ready
 - [x] future::then
 - [x] future::unwrap_or_else

src/future.rs

@@ -1,6 +1,8 @@
 use futures::future::Future;
 use futures::stream::Stream;
 
+use core::task::{Poll, Waker};
+
 pub async fn ready<T>(value: T) -> T {
     value
 }
@@ -137,6 +139,24 @@ pub fn into_stream<Fut>(future: Fut) -> impl Stream<Item = Fut::Output>
     })
 }
 
+pub fn poll_fn<F, T>(f: F) -> impl Future<Output = T>
+    where F: FnMut(&Waker) -> Poll<T>,
+{
+    use std::future::from_generator;
+    use std::future::get_task_waker;
+
+    from_generator(|| {
+        let mut f = f;
+        loop {
+            let poll_result = get_task_waker(|waker: &_| f(waker));
+            match poll_result {
+                Poll::Pending => yield,
+                Poll::Ready(value) => return value,
+            }
+        }
+    })
+}
+
 #[cfg(test)]
 mod tests {
     use futures::executor;
@@ -264,4 +284,17 @@ mod tests {
             assert_eq!(collected, vec![17]);
         });
     }
+
+    #[test]
+    fn test_poll_fn() {
+        executor::block_on(async {
+            let read_line = |_waker: &_| -> Poll<String> {
+                Poll::Ready("Hello, World!".into())
+            };
+
+            let read_future = poll_fn(read_line);
+            assert_eq!(await!(read_future), "Hello, World!".to_owned());
+        });
+    }
+
 }

src/lib.rs

@@ -1,4 +1,4 @@
-#![feature(async_await, await_macro, futures_api)]
+#![feature(async_await, await_macro, futures_api, gen_future, generators)]
 
 pub mod future;
 pub mod stream;