Add core::stream::from_iter

Author: yoshuawuyts

library/core/src/stream/from_iter.rs

@@ -0,0 +1,38 @@
+use crate::pin::Pin;
+
+use crate::stream::Stream;
+use crate::task::{Context, Poll};
+
+/// A stream that was created from iterator.
+///
+/// This stream is created by the [`from_iter`] function.
+/// See it documentation for more.
+///
+/// [`from_iter`]: fn.from_iter.html
+#[unstable(feature = "stream_from_iter", issue = "81798")]
+#[derive(Clone, Debug)]
+pub struct FromIter<I> {
+    iter: I,
+}
+
+#[unstable(feature = "stream_from_iter", issue = "81798")]
+impl<I> Unpin for FromIter<I> {}
+
+/// Converts an iterator into a stream.
+#[unstable(feature = "stream_from_iter", issue = "81798")]
+pub fn from_iter<I: IntoIterator>(iter: I) -> FromIter<I::IntoIter> {
+    FromIter { iter: iter.into_iter() }
+}
+
+#[unstable(feature = "stream_from_iter", issue = "81798")]
+impl<I: Iterator> Stream for FromIter<I> {
+    type Item = I::Item;
+
+    fn poll_next(mut self: Pin<&mut Self>, _cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
+        Poll::Ready(self.iter.next())
+    }
+
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        self.iter.size_hint()
+    }
+}

library/core/src/stream/mod.rs

@@ -122,6 +122,8 @@
 //! warning: unused result that must be used: streams do nothing unless polled
 //! ```
 
+mod from_iter;
 mod stream;
 
+pub use from_iter::{from_iter, FromIter};
 pub use stream::Stream;