From 1b1eb8a8de55ce24d677c8bcee0c6d0c11d8a786 Mon Sep 17 00:00:00 2001
From: Roman Proskuryakov <humbug@deeptown.org>
Date: Thu, 10 Oct 2019 02:04:27 +0300
Subject: [PATCH] Implement stream::once

---
 README.md     |  1 +
 src/stream.rs | 31 +++++++++++++++++++++++++++++++
 2 files changed, 32 insertions(+)

diff --git a/README.md b/README.md
index 950fdca..79deb37 100644
--- a/README.md
+++ b/README.md
@@ -53,6 +53,7 @@ Stream
 - [x] stream::iter
 - [x] stream::map
 - [x] stream::next
+- [x] stream::once
 - [x] stream::poll_fn
 - [x] stream::repeat
 - [x] stream::skip
diff --git a/src/stream.rs b/src/stream.rs
index 9fa7bb6..6c21249 100644
--- a/src/stream.rs
+++ b/src/stream.rs
@@ -38,6 +38,29 @@ where
     poll_fn(move |context| Pin::new(&mut stream).poll_next(context))
 }
 
+/// Creates a stream of a single element.
+///
+/// ```
+/// # futures::executor::block_on(async {
+/// use futures_async_combinators::stream::{once, collect};
+///
+/// let stream = once(async { 17 });
+/// let collection: Vec<i32> = collect(stream).await;
+/// assert_eq!(collection, vec![17]);
+/// # });
+/// ```
+pub fn once<F>(future: F) -> impl Stream<Item = F::Output>
+where
+    F: Future,
+{
+    crate::stream::unfold(Some(future), |f| async move {
+        match f {
+            Some(f) => Some((f.await, None)),
+            None => None
+        }
+    })
+}
+
 /// Collect all of the values of this stream into a vector, returning a
 /// future representing the result of that computation.
 ///
@@ -875,6 +898,14 @@ mod tests {
         assert_eq!(executor::block_on(next(&mut stream)), None);
     }
 
+    #[test]
+    fn test_once() {
+        let stream = once(async { 17 });
+
+        let collection: Vec<i32> = executor::block_on(collect(stream));
+        assert_eq!(collection, vec![17]);
+    }
+
     #[test]
     fn test_collect() {
         let stream = iter(1..=5);