refactor crates for better api stability (#301)

actix-utils/src/future/poll_fn.rs

@@ -0,0 +1,65 @@
+//! Simple "poll function" future and factory.
+
+use core::{
+    fmt,
+    future::Future,
+    pin::Pin,
+    task::{Context, Poll},
+};
+
+/// Create a future driven by the provided function that receives a task context.
+pub fn poll_fn<F, T>(f: F) -> PollFn<F>
+where
+    F: FnMut(&mut Context<'_>) -> Poll<T>,
+{
+    PollFn { f }
+}
+
+/// A Future driven by the inner function.
+pub struct PollFn<F> {
+    f: F,
+}
+
+impl<F> Unpin for PollFn<F> {}
+
+impl<F> fmt::Debug for PollFn<F> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("PollFn").finish()
+    }
+}
+
+impl<F, T> Future for PollFn<F>
+where
+    F: FnMut(&mut Context<'_>) -> Poll<T>,
+{
+    type Output = T;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        (self.f)(cx)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[actix_rt::test]
+    async fn test_poll_fn() {
+        let res = poll_fn(|_| Poll::Ready(42)).await;
+        assert_eq!(res, 42);
+
+        let mut i = 5;
+        let res = poll_fn(|cx| {
+            i -= 1;
+
+            if i > 0 {
+                cx.waker().wake_by_ref();
+                Poll::Pending
+            } else {
+                Poll::Ready(42)
+            }
+        })
+        .await;
+        assert_eq!(res, 42);
+    }
+}