Got further! Thx Josh!

src/stream/successors.rs

@@ -1,25 +1,31 @@
 use std::marker::PhantomData;
 use std::pin::Pin;
+use std::mem;
 
 use crate::future::Future;
 use crate::stream::Stream;
-use crate::task::{Context, Poll};
+use crate::task::{Context, Poll, ready};
 
-/// A stream that yields elements by calling an async closure with the previous value as an
-/// argument
-///
-/// This stream is constructed by [`successor`] function
-///
-/// [`successor`]: fn.successor.html
-#[derive(Debug)]
-pub struct Successors<F, Fut, T>
-where
-    Fut: Future<Output = Option<T>>,
-{
-    successor: F,
-    future: Option<Fut>,
-    next: Option<T>,
-    _marker: PhantomData<Fut>,
+
+
+pin_project_lite::pin_project! {
+    /// A stream that yields elements by calling an async closure with the previous value as an
+    /// argument
+    ///
+    /// This stream is constructed by [`successor`] function
+    ///
+    /// [`successor`]: fn.successor.html
+    #[derive(Debug)]
+    pub struct Successors<F, Fut, T>
+    where
+        Fut: Future<Output = Option<T>>,
+    {
+        successor: F,
+        #[pin]
+        future: Option<Fut>,
+        slot: Option<T>,
+        _marker: PhantomData<Fut>,
+    }
 }
 
 /// Creates a new stream where to produce each new element a closure is called with the previous
@@ -40,6 +46,7 @@ where
 /// });
 ///
 /// pin_utils::pin_mut!(s);
+/// assert_eq!(s.next().await, Some(22));
 /// assert_eq!(s.next().await, Some(23));
 /// assert_eq!(s.next().await, Some(24));
 /// assert_eq!(s.next().await, Some(25));
@@ -58,31 +65,20 @@ where
 /// # }) }
 ///
 /// ```
-pub fn successors<F, Fut, T>(start: Option<T>, func: F) -> Successors<F, Fut, T>
+pub fn successors<F, Fut, T>(first: Option<T>, succ: F) -> Successors<F, Fut, T>
 where
     F: FnMut(T) -> Fut,
     Fut: Future<Output = Option<T>>,
     T: Copy,
 {
     Successors {
-        successor: func,
+        successor: succ,
         future: None,
-        next: start,
+        slot: first,
         _marker: PhantomData,
     }
 }
 
-impl<F, Fut, T> Successors<F, Fut, T>
-where
-    F: FnMut(T) -> Fut,
-    Fut: Future<Output = Option<T>>,
-    T: Copy,
-{
-    pin_utils::unsafe_unpinned!(successor: F);
-    pin_utils::unsafe_unpinned!(next: Option<T>);
-    pin_utils::unsafe_pinned!(future: Option<Fut>);
-}
-
 impl<F, Fut, T> Stream for Successors<F, Fut, T>
 where
     Fut: Future<Output = Option<T>>,
@@ -91,23 +87,23 @@ where
 {
     type Item = T;
 
-    fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
-        if self.next.is_none() {
+    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        let mut this = self.project();
+
+        if this.slot.is_none() {
             return Poll::Ready(None);
         }
 
-        match &self.future {
-            None => {
-                let x = self.next.unwrap();
-                let fut = (self.as_mut().successor())(x);
-                self.as_mut().future().set(Some(fut));
-            }
-            _ => {}
+        if this.future.is_none() {
+            let x = this.slot.unwrap();
+            let fut = (this.successor)(x);
+            this.future.set(Some(fut));
         }
 
-        let next = futures_core::ready!(self.as_mut().future().as_pin_mut().unwrap().poll(cx));
-        *self.as_mut().next() = next;
-        self.as_mut().future().set(None);
+        let mut next = ready!(this.future.as_mut().as_pin_mut().unwrap().poll(cx));
+
+        this.future.set(None);
+        mem::swap(this.slot, &mut next);
         Poll::Ready(next)
     }
 }